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RAJIV GANDHI INSTITUTE OF VETERINARY EDUCATION AND

RESEARCH

VETERINARY SURGERY AND RADIOLOGY

Credit Hours :2+1

THEORY NOTES

UNIT-2 (VETERINARY ANAESTHESIOLOGY))

Preapared by
Dr.N.Aruljothi
Dr.N.Gurunathan, Dr.M.Vigneswari, Dr.S.Tina Roshini

Department of Veterinary Surgery and Radiology

Teaching Veterinary Clinical campus
Mettupalayam, Pondicherry-9
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INTRODUCTION TO ANAESTHESIA
It is the name given to the whole art and science relating to the production of
insensibility. Anaesthesia is a reversible process . The purpose of anaesthesia is to
produce a convenient , safe and inexpensive means of restraint so that clinical procedures
may be expedited with a minimum of pain , discomfort and toxic side effects to the
patient and to the anaesthetist .The art of anaesthesia , anaesthetic principles and
anaesthetic techniques is based on a general understanding of 1) the terms used to
describe the effects of drugs used to produce chemical restraint and anaesthesia , 2) the
pharmacology of anaesthetic drugs and 3 ) the correct methods of anaesthetic drug
administration.
HISTORY OF VETERINARY ANAESTHESIA
Year/Period Scientist/s Event
1824 H.H.Hickman Demonstrated the pain alleviating property
of mixture of N2O and O2 in dogs
1847 Flourens Chloroform for GA in animals
1853 C.P.Jackson ( Boston ) Employed ether anaesthesia in animals
1854 Dadd ( USA ) Advocated the use of Scientific principles
of anesthesia in Vet. practice
1878 Humbert Employed Chloral hydras in equines
as intravenous anaesthetic
Sir Frederick Hobday Popularised use of cocaine as LA in
( England ) animals
1898 August Bier (Germany ) Spinal anaesthesia in animals
1901 Cuille and Sendrail(France) Subarachnoid anaesthesia in animals
1901 Cathelin Epidural anaesthesia in dog
1920 Retzgen,Benesch & Brook Epidural anaesthesia in large animals
1940 Farquharson & Formston Paralumbar anaesthesia in animals
1920s GA widely employed in small animals
1950s GA in large animal initiated
1970 American Society of Veterinary Anaesthesiology formed
1975 American College of Veterinary Anaesthesiologists formed
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_________________________________________________________________
GLOSSARY
Akinesia – Loss of motor response (movement ) due to paralysis of motor nerves
Analgesia – Loss of sensitivity to pain
Analgesic agent – is a substance which temporarily abolishes awareness of pain
Anaesthesia – Total loss of sensation in a body part or in the whole body , generally
induced by the administration of a drug that depresses the activity of nervous tissue either
locally ( peripherally ) or generally ( centrally )
Anaesthetic agent – is a substance which produces , in a controllable manner , both loss
of consciousness and an absence of motor response to noxious stimuli( harmful , painful )
Local anaesthesia – It is a technique of producing reversible loss of pain to a limited
body area with minimal effects on the rest of the body .
Regional anaesthesia – Blocking conduction in sensory nerves in innervating the region
of operation. The drugs are deposited close with nerve without interference of fascial
sheath .
Local analgesic – is a substance which when applied about nerve terminals or nerve
fibres temporarily prevents the conduction of impulses by the nerve tissue
Tranquilization , ataraxia , neurolepsis – A state of tranquility and calmness in which
the patient is relaxed , awake and unconcerned with its surroundings and potentially
indifferent to minor pain . Sufficient stimulation will arouse the patient . Tranquilizers act
by depressing the hypothalamus and the reticular activating system .
Sedation – A mild degree of central depression in which the patient is awake but calm , a
term often used interchangeably with tranquilization . With sufficient stimuli , the patient
may be aroused . Sedatives act by a dose dependant depression of the cerebral cortex .
Hypnosis – Artificially induced sleep or a trance resembling sleep from which the patient
can be aroused by variety of stimuli.
Narcosis – Drug – induced stupor or sedation in which the patient is oblivious to pain ,
with or without hypnosis .
General anaesthesia – is a state of unconsciousness produced by a process of controlled
reversible intoxication of the central nervous system in which there is a lowered
sensitivity to stimuli from the environment and a diminished motor response to such
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stimuli .Ideally includes unconsciousness, hyporeflexia , analgesia , and muscle

relaxation . General anaesthesia can be produced with a single drug or by a combination
of drugs .
Surgical anaesthesia – Loss of consciousness and sensation with sufficient muscle
relaxation and analgesia to allow surgery to be performed without pain to or movement of
the patient .
Balanced anaesthesia – Surgical anaesthesia produced by a combination of two or more
drugs or anaesthetic techniques , each contributing its own pharmacological effects . The
agents used generally include tranquilizers , narcotics , analgesics and muscle relaxants .
Catalepsy – A state in which there is malleable rigidity of the limbs . The patient is
generally unresponsive to aural , visual , or minor painful stimuli .
Dissociative anaesthesia – A central nervous system state characterized by catalepsy ,
profound peripheral analgesia and altered consciousness produced by the cyclohexamine
drugs ( e.g , Ketamine ) .
Neuroleptanalgesia – Hypnosis and analgesia produced by a combination of a
neuroleptic drug and an analgesic drug .

INDICATIONS FOR ANAESTHESIA

I) Restraint : Radiography, Cleaning , grooming and dental cleaning, Bandaging,
splinting , plaster casting, Capture of exotic and wild animals, Transportation
II) Examination: Palpation, Endoscopy, Diagnosis of lameness, Diagnostic ultrasound,
Computerized axial tomography
III) Manipulation : Catheterization, Closed reduction of luxations and fractures, Wound
Care, Obstetrics
IV) Surgery
V) Control of convulsions
VI) Euthanasia and humane slaughter of food animals Eg. CO2 in pigs

TYPES OF ANAESTHESIA
( According to the route of administration )
1. Oral /Rectal : Liquid anaesthetics and suppositories
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2. Local and conduction: Topical, Local infiltration, Field Block, Regional nerve block
3. Injectable : Intravenous, Intramuscular, Subcutaneous, Intrathoracic, Intraperitoneal
Intratesticular
4. Inhalation : Gases / Vapour / with Oxygen mixture
5. Electronarcosis : Electric current is passed through the cerebrum to induce deep
narcosis
6. Transcutaneous electric Nerve Stimulation ( TENS )
Local analgesia is produced by low intensity, high frequency electric stimulation
of the skin through surface electrodes.
7. Hypnosis
8. Acupuncture: An ancient chineese system of therapy utilizing long fine needle to
stimulate acupoints in meridian to induce analgesia
9. Hypothermia: body temperature is decreased either locally or generally to supplement
anaesthesia and decrease anaesthetic drug requirement.

Effect of route on anaesthetic effect:

1.Intravenous – onset of action is immediate , but peak effect may take minutes .
Duration of action is shorter and effects are generally more intense than for other routes .
2.Intramuscular or subcutaneous - onset of action may take 10 to 15 mins , but peak
effect may not be obtained for many minutes to hours and will depend on the blood
supply to the tissues at the site of injection , drug absorption and rate of metabolism of
the drug .
3.Rapidity of injection – Faster injections generally cause more intense effects due to
decreased mixing of drug with blood .
4.Concentration of solutions
a) Increasing drug concentrations may increase intensity of immediate effect .
b) Increasing concentrations may increase vascular irritation .
5.Onset of action of inhalation drugs requires absorption of gas from alveoli into the
blood , then diffusion of anaesthetic into central nervous system.
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TYPES OF ANAESTHESIA
( based on effects produced )
1) Local analgesia
2) Regional analgesia
3) Sedation and Narcosis
4) General anaesthesia
PATIENT EVALUATION
Anaesthesia involves more than just the delivery of anaesthetic drugs to the
patient . Safe anaesthesia implies proper selection of drugs based on the procedure to be
performed as well as the physical status of the patient .
I) Patient identification
Case number / identification / Name of owner / Name of animal
Signalment: Species, Breed, Age, Sex and Body weight
II) Client complaint and anamnesis ( history)
1. Duration and nature of illness:
2. Concurrent diseases : diarrhea, vomiting, haemorrhage, epilepsy, Cardiac disorders
renal disorders
3. Level of activity :
4. Previous and current administration of drugs: Organophosphates, Insecticides,
5. Sulphonamides, Chloramphenicol, Streptomycin , neomycin , polymyxin B,Digitalis
glycosides, Beta blockers
6. Previous anaesthetic history and reactions:
7. Recent feeding:
III ) Current Physical Examination
1. General body condition: Obesity, Cachexia, Pregnancy, Dehydration etc.
2. Cardiovascular: Heart rate and rhythm, Arterial pulse, Capillary refill time and cardiac
murmurs
3. Pulmonary
a) Respiratory rate and depth
1) Usually 15-25 for small animals, 8-20 for large animals
2) Tidal volume is approximately 14 ml /kg
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b) Mucous membranes: Pallor ( anemia), Cyanosis ( > 5 g/dl of unoxygenated Hb )

c) Auscultation ( breath sounds )
d) Upper airway obstruction
e) Percussion
4. Hepatic: jaundice, Failure of blood to clot
5. Renal : Anuria, Polyuria / polydipsia
6. Gastrointestinal : Diarrhoea, Vomiting, Parasites, Distension
7. Nervous system and special senses: Seizures, Coma, Glaucoma
8. Metabolic and endocrine: Temperature, Hyperthyroid, Hypothyroid, Diabetes
9. Integument: Hydration, Neoplasia, Subcutaneous emphysema( fractured ribs )
Parasites ( fleas , mites), Burns, Trauma
10. Musculoskeletal: Weakness, Electrolyte imbalance ( hypokalemia ), Ambulatory or
non ambulatory, Fractures
IV ) Presurgical Laboratory Workup
1. Minimum laboratory evaluation: Plasma protein, PCV, Hb
2. Other laboratory tests: Blood Counts, Blood gases, Haemostasis, Temperature
3. Blood chemistry profile: Electrolytes, BUN, Creatinine, SGPT , SGOT
4. Urinalysis:
a) Specific gravity
b) Physicochemical evaluation: pH 7- 7.5 (meat diet) and 7-8 ( vegetable diet ),
Protein, Acetone, Bilirubin, Blood
c) Microscopic evaluation of urine segment: Casts, RBC, WBC, Epithelial cells,
Bacteria, Crystals
5. Electrocardiography for traumatized patients
6. Radiology: Thorax and Abdomen
PHYSICAL STATUS
I) Identity status
a) Class I – normal patient with no organic disease
b) Class II - patient with mild systemic disease
c) Class III - patient with severe systemic disease limiting activity but not
incapacitating
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d) Class IV - patient with incapacitating systemic disease that is a constant threat to

life .
e) Class V – moribund patient not expected to live 24 hours with or without
operation.
II) Emergency operation designated by “ E “ after appropriate classification.

SELECTION OF DRUG AND MODALITY

Ideal Anaaesthetic drug:
1. Does not depend on metabolism for its termination of action and elimination
2. Permits rapid induction, quick alteration in depth of anaesthesia and rapid recovery
3. Inexpensive, stable, noninflammable, nonexplosive, nonirritant to tissues
4. Does not depress caediopulmonary function
5. Doesnot require any special equipoment for administration
Selection of anaesthetics / modality
I) Selection of drugs and techniques will depend on
a) Species , breed , age and relative size of the patient .
b) Physical status and specific disease processes of the patient and concurrent
medication .
c) Demeanor of the patient and the presence of pain
d) Personal knowledge and experience
e) Available assistants and their training .
f) Familiarity with the equipment available
g) Length and type of operation or procedure to be performed
Variation in response can be expected because doses and techniques are based on
the average animal. Thus the ability to modify anaesthetic techniques is essential No drug
available possess all the above qualities, So selection of an anaesthetic is a compromise
based on appraisal of the situation like Species of the animal, Breed, Age, Physical status
of the patient, Specific needs of the species, Specific needs of the disease condition and
Familiarity of the clinician with the proposed anaesthetic technique
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PATIENT PREPARATION
I) Fasting
a) Small Animals: 12-24 hrs of food and 6-12 hrs of water
Large Animals : 24-36 hrs of food and 8-12 hrs of water (2-4 hrs in young ones)
Do not withhold food for excessive periods in neonates , animals under 5 pounds or birds
Fasting is very important in ruminants since they are risky patients for GA because of
Regurgitation, Pulmonary aspiration, Bloat, Inadequate oxygenation, Injury and
Respiratory depression and anorexia
II ) Correct or compensate for : Dehydration ( hypovolemia), Anaemia or
Hypoproteinemia, Acidosis, Cardiac dysfunction, Respiratory distress, Renal
dysfunction, Haemostatic defects and Temperature
III) Specific preparation for intended procedure: Eg.Thoracic, Abdominal, Orthopedic,
Ophthalmologic etc.
IV) Other considerations
a) Fluid and caloric needs during and following anaesthesia
b) Special medications ( antiarrhythmics )
c) Duration of surgery
d) Needs of the surgeon

LOCAL ANALGESIA
It is a technique of producing reversible loss of pain to a limited body area with
minimal effects on the rest of the body .
Factors to be considered in the choice of this technique :
1. The site , nature and expected duration of surgery – minor surgeries like abscess
opening , ophthalmic surgery , amputation of digit etc .
2. The species , temperament and health of the patient . Eg ; Animals in shock , pyometra
etc .
3. Special requirements such as minimum of fetal depression during caesarian section .
4. The skill and experience of the veterinarian .
5. Economics of time and material .
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TECHNIQUES
Surface analgesia :
Surface application : by cold (ice + salt ) or ether spray , ethyl chloride spray
Carbonic acid snow over the surface, Aqueous solutions of 2% to 4% lignocaine /
cocaine ( eye , eczema ) , proxymetacaine ( ophthaine – 0.5% ) or 5% proparacaine
HCl. 2% lignocaine in sterile carboxy methyl cellulose gel for excellent lubricant for
glans penis , urethral catheters .
Infiltration analgesia :
The nerve endings are being blocked at the actual site of operation . It can be
employed in minor surgical procedures not involving digits or teats , either in
conjunction with basal narcosis/sedation. Infiltration should not be carried out
through or into infected or inflamed tissues .
The limits of the area to be infiltrated are defined and marked for subsequent
recognition by intradermal weals using small needles ( 0.5 to 1 ml solution ) . Later
on S/C infiltration can be made through the site of weals using a 10 cm long needle
by injecting 1 ml of solution for every cm of incision . To infiltrate several layers of
tissue , puncture step by step by advancing the needle through the deeper tissues .
Disadvantages of infiltration analgesia :
a ) Incomplete analgesia and muscle relaxation of deeper layers of abdominal wall .
b ) Toxicity after injecting significant amounts of analgesic solution into the
peritoneal cavity .
c ) Increased cost due to larger doses of analgesics and longer time required .
Field block :
It is the procedure of making walls of analgesia enclosing the operation field . It
is accomplished by making fan like injections in certain planes of the body so as to
soak all the nerves which cross these planes on their way to the operation field , but
no attempt is made to pick up the nerves individually . Generally , walls of the
analgesia are created obliquely to the skin surface , involving only part of the tissues
around the region , but meeting below so that the operation area is held in a soft cup
of infiltrated tissue.
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Advantages :
1. Deposition of analgesic away from the site
2. Absence of distortion of anatomical features in the line of incision .
3. Ischaemia of the tissues within the blocked area .
4. Muscular relaxation .
5. Minimzing oedema , haematoma and possible interference to healing of the wound
Methods: Fan shaped, Cone / cup shaped area of infiltration, Inverted or “ L “ block or “
T “ block in paralumbar fossa in cattle, Ring block ( injection in transverse plain above
the level of amputation of extremities) . Vasoconstrictors should not be added to
solutions used to produce ring blocks in teats, since it may result in ischaemic necrosis

LOCAL ANALGESICS
AGENT TRADE DOSAGE DURATION
NAME AND ACTION
1) Cocaine 4% installation into eye
10-20% nasal & laryngeal mucosa .
2) Procaine Novocaine 1-2% for infiltration and nerve block 30-60 min.
(NB)
3)2- chloroprocaine Nesacaine 1-2% for infiltration and nerve block 30-60 min.
(NB)
4)Lignocaine Xylocaine 0.5-2% LI & NB 90-180 min.
2-4% topical
5) Mepivacaine Carbocaine 1-2% LI 90-180 min.

6)Hexylcaine Cyclaine 0.5-1% LI , 2% nerve block 90-180 min.

5% Topical
7)Tetracaine Pontocaine 0.1% for LI & NB 180-300 min.

8) Bupivacaine Marcaine 0.25% for LI 180-300 min.

0.5% for NB
0.75%epidural

9) Dibucaine Nupercaine 0.1% topical 180-300 min.

10)Propoxycaine 0.4 % for dental anaesthesia 180-300 min.

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Mechanism of action :
Inhibition of the excitation conduction process in peripheral nerves . Local
analgesic drugs are generally water soluble acid salts . In solution , they exist in both a
charged cationic (+) and uncharged base forms . After deposition into tissue , which has
slightly alkaline pH , the alkaloid base is liberated . The free base of the analgesic then
diffuses readily across the nerve sheath , where it is absorbed at the outer lipid membrane
of axon . The amino group of the drug interact with the polar groups of the cell
membrane to prevent the inflow of sodium and subsequent ion flow – phase 0
depolarization and conduction of impulse cannot occur .
Another important mechanism involves calcium as a membrane stabilizing agent .
Alteration in membrane Ca++ is responsible for deformation or expansion of the cell
membrane and thus blockade in the transmission or conduction of nerve impulses.
Potentiation of drugs :
1) Vasoconstrictor : Epinephrine at a concentration of 1 : 200,000 i.e. adding 0.1 ml of
1 : 1000 ( 0.1 mg ) epinephrine to 20 ml of local analgesic.
Disadvantage : Local necrosis , risk of cardiac arrhythmia and ventricular
fibrillation .
2) Hyaluronidase @ 150 turbidity reducing units ( TRU ) / 25 ml to enhance diffusion .
Increased diffusion results in faster onset of action , but also shortens the duration
due to the increased permeability of the tissues .
The combination of hyaluronidase , epinephrine and procaine hydrochloride
solution ( 1% ) will double the area of desensitization and increase five fold the duration
of analgesia.
Apparent signs of toxicity to LA
It may be due to overdose or intravenous injection. Signs include excitation , lateral
recumbency, generalized tonic – clonic convulsions , opisthotonus , respiratory
depression and cardiac arrest .
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REGIONAL ANALGESIA :
Blocking conduction in sensory nerves in innervating the region of operation. The
drugs are deposited close with nerve without interference of fascial sheath .
HEAD REGION
Equine

1. Supraorbital nerve block : The Upper and lower boarders of the supraorbital process,
close to its junction with the main mass of frontal bone is palpable. The foramen is
recognized as a pit like depression midway between the two boarders. The needle is
passed into the foramen for 1 cm to deposit the solution. It will desensitize the skin of
the upper eyelid and the forehead .
2. Infraorbital nerve block : At its point of emergence from the infraorbital foramen –
desensitize skin of the lip, nostrils and face on that side upto the level of foramen – for
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15-20 min.
3. Mental nerve block : At its emergence from the mental foramen for analgesia of
lower lip on that side
EYE
Cattle :
I) Analgesia of eyelid
Indications : Removing foreign bodies from cornea , conjunctival sac and
Subconjunctival injections .
Methods:
a) 10 ml of a 2 % Lidocaine hydrochloride solution is injected S/C on a line about 0.5 cm
from the margins of the dorsal and ventral eyelids at multiple sites 0.5 cm apart .
b) Auriculopalpebral nerve block ( B)– Branch of facial nerve . Causes motor
paralysis of eyelid . By injecting 5 – 10 ml of a 2 % lidocaine hydrochloride solution S/C
anterior to the base of the auricular muscles , where the nerve is sometimes palpable in a
notch on the zygomatic arch .

II ) Anaesthesia for enucleation :

a) Retrobulbar – Through upper and lower eyelids or the lateral and medial canthii are
the sites for needle placement .
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When using medial canthus approach , the needle is inserted in the form X of the
conjunctiva caudal to the nictitans and dorsomedial to the operators finger . As the needle
is inserted in the orbital apex , the medial wall of the bony orbit is felt . In cattle 10 – 15
ml of 2% LH is injected in small increments using a 8 – 12 cm long 18 G needle .
Corneal analgesia , mydriasis and proptosis indicate a satisfactory RNB .
b) Peterson eye block –(A) The notch formed by the supraorbital process cranially , the
zygomatic arch ventrally and coronoid process of the mandible caudally constitute the
site for needle placement for the peterson eye block . 12 cm , 18 G needle – 15 ml of 2
% LH . The needle is inserted horizontally and slightly posterior direction in the notch
until it strikes the coronoid process of the mandible . Then the needle is gently
manipulated off and advanced in into the pterygopalatine fossa rostral to the
orbitorotendum foramen which is at a depth of 7.5 to 10 cm . The oculomotor,
trochlear and abducens nerves and 3 branches of trigeminal , ie. , the ophthalmic ,
maxillary and mandibular are desensitized at the site of emergence from foramen
orbitorotendum .
Effect – Both these techniques prevent blinking of eye for several hours .
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NASAL REGION
Cattle : Infraorbital nerve block
Infraorbital nerve is blocked at its point of emergence from the infraorbital canal .
The foramen is located rostral to the facial tuberosity on a line extending from the
nasomaxillary notch to the second upper premolar – 20 –30 ml 2% lidocaine may be
injected .
HORN
Cornual nerve block: Cornual nerve is a branch of zygomaticotemporal ( lacrimal )
portions of the ophthalmic division of the trigeminal nerve ( CLOT ) .
Indications – Dehorning cattle and goats , disbudding young kids .
Cattle - A 2.5cm , 20 G needle is inserted through the skin approximately 2.5cm anterior
to the base of the horn and lateral to the palpebral temporal bridge of the frontal bone .
Needle penetration is 1 cm . 10 ml solution may be injected .

Goat – The horn is supplied by cornual branch of lacrimal and infratrochlear nerves .
Site – Halfway between the lateral canthus of the eye and the lateral base of the horn
( cornual branch of the lacrimal nerve ) and halfway between the medial canthus of the
eye and medial base of the horn ( cornual branch of the infratrochlear nerve ) . 2-3 ml
solution may be injected .
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For disbudding in young kids , a ring block of the horn base can be made by
injecting not more than 0.5 ml of 2% LH solution .

DENTAL ANALGESIA
Equine: Mandibular nerve block : Caudal boarder of the mandible, about 3 cm below
the temperomandibular articulation. The needle is directed towards medial boarder of the
ramus to reach the point. – desensitize the lower molars
Dogs
1) Infraorbital nerve block– 2 sites
a) In the pterygopalatine fossa at its point of entry into infra orbital canal . All the teeth in
the upper jaw on that side will be desensitized . A point 4 cm below the lateral canthus of
the eye , in the space between the posterior border of the malar bone and the anterior
border of the coronoid process of the mandible .
b) In the lower part of the infra orbital canal , injection being made through the infra
orbital foramen . Analgesia of the incisors , canine and first two premolars will develop .
Injection is made through the gum . The upper lip is retracted and the tip of the
infraorbital foramen will be readily detected immediately over the third premolar teeth ,
insert the needle into the foramen .
2) The mandibular nerve block
On the medial aspect of the ramus at the mandibular foramen – all the teeth in the lower
jaw on the side will be desensitized . If the finger is passed along the posterior part of the
ventral border of the ramus , a depression will be felt . The middle of the depression is the
point of insertion of the needle .
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a) In the anterior part of the mandibular canal , injections being made through the
mental foramen. The mental foramen is situated immediately beneath the anterior root
of the second premolar tooth which can be felt by retracting the gum. Loss of
sensation in the lower incisors , canines and first two premolars were effected

PARALUMBAR FOSSA
Cattle -For obtaining analgesia of the paralumbar fossa, 4 techniques are described :
1) Proximal paravertebral analgesia
2) Distal paravertebral analgesia
3) Segmental dorsolumbar epidural analgesia
4) Thoracolumbar subarachnoid analgesia
1) Proximal paravertebral analgesia :
Synonyms : Farquharson , Hall or Cambridge technique.
The dorsal and ventral nerve roots of the last thoracic ( T13 ) and 1 st and 2nd lumbar ( L1
& L2 ) spinal nerves are desensitized as they emerge from the intervertebral foramina.
The site at the cranial edges of the transverse processes of L1 , L2 and L3 and at a
point 2.5 to 5 cm off the dorsal midline is prepared aseptically and skin is desensitized .
The needle is passed ventrally to desensitize T13 until it contacts the transverse process
of L1 . The needle point is advanced of the cranial edge of the transverse process
approximately 1 cm to pass through the intertransverse fascia . Using 2.5 cm needle , 5 –
10 ml of 2 % LH are injected with little resistance to desensitize the ventral branch of
T13 . The needle is withdrawn 1 – 2.5 cm to above the fascia and dorsal surface of the
transverse process and inject 5 ml of solution to desensitize the dorsal branch of the
nerve. L1 and L2 are desensitized similar to T13 .
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Effects: starts within 10 mins and lasts for 90 min. There will be Analgesia of skin ,
scoliosis towards the desensitized side due to the paralysis of paravertebral muscles ,
increased sin temperature due to increased blood flow after paralysis of cutaneous
vasomotor nerves .
Advantages :
1) Small doses of analgesic needed .
2) A wide and uniform area of analgesia and muscle relaxation .
3) Minimal intra abdominal pressure .
4) Increased intestinal tone and motility due to desensitization of sympathetic
fibres of rami communicates .
5) Absence of local analgesia from the operative wound margins .
Disadvantages :
1) Technical difficulty .
2) Arching up of the spine due to paralysis of the back muscles .
3) Risk of penetrating vital structures such as the aorta and thoracic
longitudinal vein on the left side and the caudal venacava on the right side.
4) Caudal migration of injection site to femoral nerves with subsequent
paresis .
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2 ) Distal paravertebral analgesia :

Synonyms : Magda , Cakala or Cornell technique .
The dorsal and ventral rami of the spinal nerves T13 , L1 and L2 are desensitized
at the distal ends of L1 , L2 and L4 . A 7.5 cm long needle is inserted ventral to the tips
of the respective transverse processes in large ruminants where approximately 10 – 20 ml
of a 2% LH are injected in a fan shaped infiltration pattern . The needle is completely
withdrawn and reinserted dorsal to the transverse process , in a slightly caudal direction
where the cutaneous branch of dorsal rami is injected with 5 ml of analgesic . The
procedure is repeated for the 2nd and 4th lumbar transverse processes .

Advantages :
1. Use of more routine size needles .
2. No risk of penetrating major vessels .
3. Lack of scoliosis and minimal weakness to pelvic limbs .
4. Minimal ataxia .
Disadvantages : Larger doses of anaesthetics and variation in efficiency exists .

3) Segmental dorsolumbar epidural anaesthesia: Synonym – Arthur block

Local analgesic is injected into the epidural space either between L1 and L2
vertebrae or less commonly between T13 & L1 to desensitize the nerve roots as they
emerge from the dura covering the spinal cord .
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The skin area caudal to T13 or L1 spinous process and contra lateral to the flank
region to be desensitized is aseptically prepared and anaesthetized . The spinal needle is
inserted through a canula for a distance of 8 – 11 cm while being directed ventrally and
medially at an angle of 10 – 15 degrees to vertical . After piercing the interarcuate
ligament , the needle must not be inserted further .
Dose – 8 ml of 2% LH / 500 kg BW
Time – 7 – 20 mins – lasts for 45 – 120 mins .
Advantages :
1. One injection with small quantity of analgesics .
2. Uniform analgesia , relaxation of skin , muscle and peritoneum .
Disadvantages :
1. Technical difficulty .
2. Loss of motor control of pelvic lI/Mbs .
3. Physiological disturbance to overdose or subarachnoid injection .
4. Chance of trauma to spinal cord / meninges .
4) Thoracolumbar subarachnoid analgesia
Analgesic is injected to subarachnoid space at lumbosacral ( L6 – S1 )
intervertebral space . After getting the needle ( 17.5 cm ) to subarachnoid space , stylet is
removed , aspirate 2 – 3 ml of CSF . A catheter ( Formocath polyethylene ) 80 – 100 cm
long is advanced to T13 – L1 space . Remove 1 – 2 ml of CSF and 1.5 to 2 ml of 2 % LH
or 5% pH is injected @ 0.5 ml / min . Time – 6 – 10 mins , lasts for 20 – 80 mins .
Surgical analgesia is easily maintained by fractional bolus administration of 0.5ml
analgesic at 30 mins interval .
Advantages with respect to Arthur block
1. Simplicity of needle and catheter placement .
2. Minimal dosage .
3. Analgesic deposited at nerve root .
4. Rapid onset .
5. Minimal physiological disturbance and minimum anaesthetic needed .
Disadvantages :
1. Kinking and cushing of catheter .
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2. Trauma to conus medullaris .

3. Accidental vascular puncture .
4. Precise dosage .
5. Radiography for confirmation of positioning of catheter .

EPIDURAL ANALGESIA
Cattle : 1. Sacrococcygeal or Caudal Epidural anaesthesia

Indications: Obstetric procedures, surgeries of erineum,rectum,vulva,vagina,prepuce,skin

and scrotum.
Site: Sacrococygeal (S5 & Co1) and Intercoccygeal Co1 and Co2)

Procedure: The skin over Co1 and Co2 joint is prepared and desensitized with 2-3 ml of
LA. Locate the site by pumping action of the base of the tail. A needle of 3.75 to 5 cm
long, 18 G is inserted in a median plane to pierce the interarcuate ligament and directed
ventrocranially at an angle of 10o to vertical. Aspirate the contents to ensure puncturing
of vessel and inject the solution slowly according to the efferct generated.
Dose: 1ml of 2% LH/100 kg BW @ 1 ml/sec for sacrum and perineum
0.5 mg Xylazine / kg B.W diluted to 5 ml solution can also be used to effect.

2. Lumbosacral or Cranial Epidural anaesthesia

15 cm long, 20G needle – Chance of injuring the spinal cord is more
Drugs employed: 1ml of 2% LH / 4.5 kg.Bwt., effects starts with 10-20 min and
prolonged for 60-120 min.
 23

Drug: 1 ml of 0.5% Bupivacaine / 4.5 kg.

Area sensitized: Hindlimbs and abdomen behind umbilicus

Sheep and Goats: Same site. 2.5-3.75 long 18g needle is used

Pigs: Lumbosacral Epidural – between L6 & S1

6-8 cm long needle, 20g for piglets
10-16 cm long needle,18g for pigs more than 100kg.

Dogs : Lumbosacral Epidural anaesthesia

Indications: Caeserian section,surgical procedures of regions caudal to umbilicus.
Procedure: Dogs are sedated / tranquilized, and LH is injected using 2.5 to 7.5 cm,
20-22g spinal needle as a single dose.
The iliac prominence of either side of the spine are palpated by using the thumb
and middle finger of one hand. The spinous process of the 7 th Lumbar is located with the
index finger. The lumbosacral interspace should be palpated from both the cranial and
caudal directions by moving the finger on the dorsal spinous process of L6-L7 and S2-S1.
The needle must be correctly placed on the midline and caudal to L7 spinous process and
is inserted until a distinct popping sensation is left as the needle point penetrates
interarcuate ligament. Movement of the tail may indicate that the needle has engaged
nerve tissue.The epidural space is best identified by the loss of resistance test

PUDIC ( INTERNAL PUDENTAL) NERVE BLOCK

Pudic nerve is made up of fibres arising from the ventral branches of the 3 rd and
4th sacral nerves . It passes downwards and backwards in the medial surface of the
sacrosciatic ligament where it is in association with the middle haemorrhoidal nerve to
cross the lesser sacrosciatic foramen where it is accompanied by the internal pudic
vessels and pass along the floor of the pelvis to the ischial arch supplying motor fibres to
the urethra and erector and retractor muscles of penis , along with middle haemorrhoidal
nerve sensory fibres to the skin on either side of the midline from beneath the anus
downwards to the scrotum .
 24

Technique :
Locate the pudic nerve per rectum near lesser sacrosciatic foramen . Prepare the
skin over the ischiorectal fossa ( ventrally – ischial tuberosity , laterally – by posterior
border of the sacrosciatic ligament , medially by rectum and tail head ) . 15 cm long
needle is inserted at the point of the deepest depression of the fossa Immediately medial
to the ligament and directed forwards and downwards direction – 5 –7 cm depth – deposit
20 – 25 ml and 10 – 15 ml at a point little behind and above to desensitize middle
haemorrhoidal nerve .
 25

DIGITAL NERVE BLOCK

Cattle: Forelimb

1. Dorsal metacarpal nerve (A): Middle of the metacarpus,medial to extensor tendon

2. Dorsal branch of Ulnar nerve (D): 5 cm above the fetlock,on the lateral aspect of the
limb, in the groove between suspensory ligament and the metacarpal bone.
3. Palmar branch of Ulnar nerve( C ): 5 cm above the fetlock,on the lateral aspect of
the limb, in the groove between suspensory ligament and the flexor tendon.
4. Lateral branch of median nerve: palmar aspect on the midline, just above the fetlock
5. Medial branch of median nerve: 5 cm above the fetlock,on the medial aspect of the
limb, in the groove between suspensory ligament and the flexor tendon.
Hindlimb
1. Superficial peroneal nerve: upperthird of the metatarsus on dorsal midline
2. Deep peroneal nerve: Dorsal midline at a point half way between hock and fetlock
3. Plantar metatarsal nerve: Medial and lateral side of the limb in the depression
between the suspensory ligament and the flexor tendon, about 5 cm proximal to the
fetlock joint

Sheep and goats : the sites are same

 26

Horse: Fore limb

1. Median nerve: A point on the medial aspect of the limb,about 5 cm distal to the elbow
joint where the nerve lies immediately caudal to the radius and cranial tom the internal
flexors.
2. Ulnar nerve: Caudal aspect of the limb,10 cm proximal to the accessory carpal bone.
3. Musculocutaneous nerve: Medial aspect of the limb,where it lies on the surface of the
radius, halfway between the elbow and the carpusimmediately adjuscent to cephalic
vein
Hind limb
1. Tibial nerve: 1.5 cm above the point of tarsus on medial aspect in a groove between
gastrocnemius and the deep digital flexor tendons.
2. Peroneal nerve: On the lateral aspect – superficial and deep branches are best blocked
simultaneously in the groove between the tendons of the long and lateral digital
extensors about 10 cm proximal to the lateral malleoles of tibia

PREMEDICATION IN ANAESTHESIA

INDICATIONS

1.To relieve anxiety, thus overcoming the apprehension , fear and resistance to
anaesthesia.
2. To induce sedation .
3. To provide analgesia and muscle relaxation .
4. To decrease airway secretion and salivation .
5. To decrease quantity of potentially more dangerous drugs used to produce sedation ,
analgesia or general anaesthesia.
6. To minimize autonomic reflex activity .
7. To decrease gastric fluid volume and acidity .
8. To promote smooth induction and recovery from anaesthesia
 27

CLASSIFICATION

I ) ANTICHOLINERGICS: They reduce salivation and bronchial secretion, block the

effects of impulses in the vagus nerve, block certain effects produced by the drugs which
stimulate the parasympathetic system .

1) ATROPINE SULPHATE -
Alkaloid from Atropa belladonna.
Dog – 0.02 to 0.05 mg/kg I/M , S/C , IV
Cat – 0.1 to 0.3 mg/kg
Pig – 0.06 to 0.08 mg/kg
Ruminants – not generally recommended
Cattle – 0.04 to 0.06 mg/kg
Sheep and goat – 0.7 mg/kg
Available as 1 ml ampoule and 10 ml vial at a concentration of 0.6 mg/ml .

2 ) GLYCOPYRROLATE ( Robinul – v )
It is a quarternary ammonium anticholinergic agent – 5 times potent than Atropine
sulphate .
Dogs – 0.005 – 0.01 mg/kg
General dose rate – 0.01 – 0.02 mg/kg

3) HYOSCINE -
An alkaloid from Hyoscyamus niger , not widely used in animals .

II ) TRANQUILIZERS

1) PHENOTHIAZINES – Antiepileptic, Antiemetic, Produce Mental calming and

suppression of sympathetic nervous system,

a) Acepromazine maleate ( Promace )

General dose for sedation – 0.025 – 0.1 mg/kg I/M
Dogs – 0.03 – 0.1 mg/kg
Cats – 0.03 to 0.1 mg/kg
Horses – 0.044 – 0.088 mg/kg IV or I/M
Cattle – 0.01 – 0.02 mg/kg
Caprine – 0.1 to 0.2 mg/kg IV
Pig – 0.11 to 0.44 mg/kg IV or I/M

b) Propionyl promazine -
Horses – 0.15 – 0.25 mg/kg
Dogs – 0.2 to 0.3 mg/kg

c) Chlorpromazine hydrochloride ( Largactyl )

 28

Limited use in large animal anaesthesia.

Horse – 1.1 to 2.2 mg/kg IV or I/M
Cattle – 0.2 to 1.1 mg/kg
Dogs – 1 – 2 mg/kg

d) Triflupromazine hydrochloride ( Siquil ) -

Limited use in large animal anaesthesia .Available as 5 ml vials at a concentration
of 20 mg/ml .
Dogs – 1 mg/kg IV , 2 mg/kg I/M

2) DROPERIDOL -
Butyrophenone tranquilizer normally combined with fentanyl .

III ) SEDATIVES

1) BENZODIAZEPINES : Antianxiety action, Sedation, Hypnosis, Anticonvulsant,

Muscle relaxation and Retrograde amnesia (species and dose dependant)

a) Diazepam – (Valium )
5 mg , 10 mg tabs and 10 mg / 2 ml injection .
Dog & cat – 0.1 – 0.5 mg/kg IV
0.3 – 1.0 mg/kg I/M
Horse – 0.05 to 0.2 mg/kg IV
Cattle – 0.25 mg/kg I/M
Sheep – 0.5 to 1.0 mg/kg I/M
Pig – 0.5 to 1.0 mg/kg I/M

b) Midazolam – ( Versed )
Normally combine with ketamine , thiobarbiturate @ 0.1 – 0.2 mg/kg I/M

c) Climozolam -
Cattle – 5 mg/kg orally
Dogs – with fentanyl @ 1 – 1.5 mg/kg

d) Zolazepam -
Available as tiletamine ( a dissociative anaesthetic) -zolazepam combination
(TELAZOL)
Dogs – 4 – 8.6 mg/kg I/M
Cats – 6 – 16 mg/kg I/M

2 ) ALPHA – 2 ADRENOCEPTOR AGONISTS

They acts at presynaptic alpha 2 receptors causing a decrease in release of

norepinehrine and dopamine causing CNS depression, Profound sedation and varient
analgesia and muscle relaxation .
 29

a) Xylazine Hydrochloride ( ROMPUN, XYLAXIN , XYLOCAD )- IV ,I/M , S/C

First reported Alpha 2 agonist. Used as sedative and analgesic

Sedative effects commences within 10-15 min. if given IM and 3-5 min by IV
Sedative effects lasts for 1-2 hrs and analgesic effects for 15-30 min. only
Side Effects: Bradycardia, partial AV block,decrease in intestinal motility, emesis in
dogs, periodic awakening, In ruminants it may cause ruminal atony , bloat ,
regurgitation with aspiration , salivation and polyuria and Oxytocin like
effect on uterus
Available as 2 ml , 10ml , 30 ml vials with concentration of Xylazine 20 mg/ml.
Dose: Horses – 0.5 – 1.1 mg/kg IV
1 – 2 mg/kg I/M
Cattle – 0.03 – 0.1 mg/kg IV
0.1 – 0.2 mg/kg I/M
Goat – 0.01 – 0.5 mg/kg IV
0.05 – 0.5 mg/kg I/M
Dogs and cats – 0.5 – 1 mg/kg IV
1 – 2 mg/kg I/M
Contraindications –
 In obstruction of oesophagus
 Torsion of stomach
 Hernia etc .

It can be combined with Acepromazine in horses, Butorphanol in equines and bovines

and with Ketamine in dogs and cats

b) Detomidine – ( Dormosedan )

Dog – 5 – 20 microgm /kg

Horse – 10 – 40 microgm/kg
Cattle – 10 – 40 microgm/kg

c) Medetomidine – ( Newet )

Cat – 40 – 80 microgm/kg
Dog – 10 – 40 microgm /kg
Horse – 10 – 30 microgm /kg
 30

Cattle – 20 – 50 microgm /kg

Pig – 30 – 80 microgm /kg

d) Romifidine -
Horse – 30 – 80 microgm / kg

IV ) ANALGESICS

1) NON OPIOID ANALGESIC AGENTS

a) Alpha-2 agonists – will provide sedation and analgesia .

Eg. Xylazine and detomidine

b) Non steroidal anti-inflammatory drugs – will provide mild analgesia without sedation .
Eg . Phenylbutazone , Ketoprofen , and Aspirin

2) OPIOD ANALGESICS

a) Morphine sulphate -
General dose – 0.1 – 0.3 mg/kg I/M
Available as 10mg Tab; Inj.-10 mg/ml.

b) Meperidine hydrochloride ( Pethidine )

Large animals – 1 mg/kg I/M
Dogs – 1 –2 mg/kg I/M
Cats – 10 – 20 mg/animal
Available as 1 ml , 2ml amp with concentration 50 mg/ml.

c) Methadone ( Amidone )
Horse – 0.1 mg/kg IV or I/M
Dogs – 1 mg/kg IV or I/M

d) Oxymorphone hydrochloride ( Numorphon )-semisynthetic opoid

Horse – 0.022 mg/kg IV or I/M

e) Fentanyl citrate ( Fenilate, Fent )

50 times potent than morphine .
Available as 2 ml amp., with concentration of 50 microgm/ml.
Horse – 0.2 mg/kg I/M
Dogs – 0.04 mg/kg IV
Pig – 1 ml / 9-14 kg BW
Dogs – 1 ml / 30-60 lb BW

f) Etorphine Hcl ( M 99 )
Exclusively used in wild animals @ 0.5 mg / 500 kg BW I/M
 31

g) Buprenorphine ( Tidigesic, Buprigesic )

Available as 1 ml , 2ml amp with concentration 0.3 mg/ml.
Dogs – 6 – 10 microgram / kg
Horse – 6 microgram / kg

h) Butorphanol tartrate ( Torbugesic ) – Synthetic opoid analgesic

Horses : 0.22 mg/kg
Dogs : 0.1 – 0.3 mg/kg

i) Pentazocine lactate ( FORTWN , DOLOWIN)

Available as 1 ml , 10ml , with concentration 30 mg/ml.
Horse – 0.5 – 3.0 mg/kg IV
0.5 – 6.0 mg/kg I/M
Dogs and pigs – 2 mg/kg I/M

V) TRANQUILIZER AND OPOID ANALGESIC COMBINATIONS

a) Innovar vet – It is a neuroleptanalgesic containing

Fentanyl Citrate (0.4mg) and Droperidol ( 20mg)/ml
Pig – 1 ml / 9-14 kg BW
Dogs – 1 ml / 30-60 lb BW

b) Immobilon LA – Combination of Etorphine & Acepromazine for large animals

c) Immobilon SA – Combination of Etorphine & Methotrimeperazine for small animals

VI ) MUSCLE RELAXANTS

General Effects : Muscle relaxation, respiratory paralysis at higher doses, No analgesia

and increased intraabdominal and intraocular pressure
Indications: Short procedures like intubation and used in conjunction with GA under
ventillation
Contraindications: Debilitated animals and animals with hepatic diseases, excited animals
Side effects: Respiratory failure, dyspnoea, muscle weakness, paralysis

a) Centrally acting: It disrupts the impulse transmission at connecting neurons in the

spinal cord and brain stem
Eg. Guaifenesin ( GECOLATE )- Chemically similar to Mephenesin
Skeletal muscle relaxant with little effect on cardiovascular and respiratory
systems. Commonly used as inducion agent for inhalation anaesthesia in large
animals. 5% solution in Dextrose @ 110 mg/kg to effect IV. It can be used in
combination with ultrashort acting barbiturates, Xylazine and ketamine

b) Perpherally acting :
 32

i. Depolarizing blocking agents – since they are similar to neuromuscular transmitters

pharmacologically, they stimulate cholinoceptors to open the central pore or ion channel,
allowing inflow of Na and Ca ions and outflow of K ions. Depolarization occurs at
endplates. Since these molecules persists for longer period than acetyl choline, end plate
depolarization is prolonged, leading to an area of inexitability on the muscle membrane.
The muscle fibres become flaccid and relaxation ensures.

Eg. Succinyl choline ( SCOLINE, SUXOMIN, MIDARINE )

Available as 2 ml , 10ml , with concentration 50 mg/ml.
Horse – 0.088 mg/kg IV
Cattle and goat – 0.02 mg/kg
Dogs – 200 – 400 microgram /kg IV

Suxamethonium ( SCOLINE )
Commonly used in veterinary practice .
Horse – 0.12 mg/kg IV
Cattle and ovine – 0.02 mg/kg IV
Dogs – 0.3 mg/kg IV

ii) Non depolarizing blocking agents – They recognize the acetyl choline receptors and
show affinity for it, but do not trigger it. The molecules of these agents are large and
prevent acetyl choline from occupying the trigger site of receptors. They also likely to
block the ion channel causing nondepolarizaion and relaxation

Eg. Atracurium ( Tracurium )

Horse – 0.085 –0.2 mg/kg IV
Ovine – 4 –7 microgram / kg IV
Dogs – 200 – 400 microgram / kg IV

Pancuronium ( PAVULON, PANURON, NEOCURON ))2qa

Steroidal type nondepolarising peripheral muscle relaxant .
Horse – 0.12 – 0.18 mg/kgIV
Cattle – 0.043 mg/kg IV
Ovine – 0.005 mg/kg IV
Dogs – 22 – 60 microgram/kg IV

Gallamine ( FLAXEDIL )
Commonly used in veterinary practice .
Horse – 0.5 – 1 mg/kg IV
Cattle – 0.5-1 mg/kg IV
Ovine – 0.4 mg/kg IV
Dogs – 1 mg / kg IV
 33

BASAL NARCOSIS

Basal narcosis is a stage of narcosis at which the animal is unconscious but still is
capable of responding to painful stimuli. Inducing basal narcosis before administration of
general anaesthesia is desirable because it reduces the quantity of anaesthetic required
and thus increases the safety margin . The involuntary excitement during induction is
minimized , the onset becomes smooth and regular and a uniform depth of anaesthesia is
more easily maintained
Light narcosis: The animal may be able to keep standing but its responses to external
stimuli are reduced.
Medium narcosis: The animal is unable to stand but in the recumbent position it may
struggle and try to get up unless properly restrained. It is sufficient to perform operations
combined with local and regional anaesthesia.
Deep narcosis: It is very close to the stage of anaesthesia , there is muscular relaxation
and responses to external stimuli are very sluggish though not absent .
Drugs commonly used for basal narcosis are Chloral hydras , Pentobarbitone
sodium (Nembutal) .
1 ) Chloral hydras :-
Water soluble crystals, but chemically incompatible with alkalies . It cause
cerebral and autonomic depression providing poor analgesia and slight muscle relaxation.
It is a n irritant drug having narrow therapeutic index. Death may occur due to respiratory
failure and circulatory depression. The drug can be used as general anaesthetic also by
increasing beyond the narcotic dose . Toxic doses cause death by respiratory failure and
circulatory depression . Chloral hydras is the best basal narcotic for horse and adult cattle.
Can be used in pigs also .The drug can be administered by stomach tube and IV
injections.
Dose – Cattle: 5 to 6 gms per 50 kg BW of 10% solution IV or 60ml . orally
Horse : 44-66 mg/kg of 12% solution IV or 30-90 ml orally.
 34

Onset within 15-20 min. and duration 40-120 min. Most often Chloral hydras is
combined with Magnesium sulphate ( CHLOROMAG ) and Pentobarbital
(EQUITHESIN ) to allow lower amount of chloral hydras to be used.

2 ) Pentobarbitone sodium ( Nembutal ) :-

It is a good basal narcotic for small animals , calves and foals used IV as a 6.5 %
solution @ 2 mg/kg. It is not generally used alone in large animals because of its cost ,
prolonged action and due to the excitement and struggling produced during the stage of
recovery . For dogs and cats it is given IV as a 3 to 6% solution upto effect. Caprine and
swine 6.5% solution @ 26 mg/kg IV.
GENERAL ANAESTHESIA
General anaesthesia is a state of unconsciousness combined with loss of sensitivity and
reduced motor response to stimuli , produced in a controlled manner by a process of
reversible intoxication of the central nervous system.
Produced by
1) Inert elements
2) simple inorganic compounds -nitrous oxide)
3) halogenated hydrocarbons - halothane )
4) complex organic structures - barbiturate )
These drugs are generally administered by an anesthesiologist in order to induce or
maintain general anesthesia to facilitate surgery.

MODE OF ACTION OF GENERAL ANAESTHETICS

There are several theories about the action of anaesthetics , but none of those
have been accepted as completely satisfactory .
1 ) The colloid theory
According to this theory , anaesthesia is brought about by the reversible
aggregation of cell colloids . Aggregation of colloids in the cell is brought about with the
onset of anaesthesia and this is reversed with the recovery from anaesthesia . Although
this theory may to some extent explain changes brought about in the cells of lower forms
 35

of life like amoeba , by the anaesthetic drugs , the action produced in higher species of
animals appears to be not so simple .
2 ) Lipoid (Lipid ) solubility theory
Mayer ( 1877) brought out a theory that : “ All chemical substances which are
soluble in fats or fatty substances , must exert a narcotic action on living protoplasm , in
so long as they become distributed in it “ . In other words , the capacity of an anaestheic
drug to act depends on its solubility in fats (lipoids ) . It has been observed , however ,
that certain drugs soluble in fats cause convulsions and not depression or anaesthesia and
this questions the lipoid theory . Further it is argued that even though the fat solubility
may overthrow some light on how the drug is brought to the CNS , it does not
satisfactorily explain the mode of action of the drug . It is also worthwhile to note that
certain drugs like morphine which are insoluble in fats are still capable of bringing about
narcosis .

3 ) Cell permeability theory

This theory assumes that anaesthesia is produced because of the capacity of the
drug to affect the permeability of the cell membrane , thereby altering the cellular
constitution ; but it also is not satisfactory because drugs like digitalis which affect cell
permeability do not cause anaesthesia .
4 ) Biochemical theory
It has been proved experimentally that there is decreased oxygen consumption
during anaesthesia and therefore decreased oxygen consumption brought about in the
brain tissue by certain biochemical changes was proposed as the cause of anaesthesia .
The decrease in oxygen consumption might be only a reflection of the decreased
metabolic activity resulting from anaesthesia . Hence this theory indicates only a
phenomenon resulting from anaesthesia and does not explain the mechanism of
production of anaesthesia .
5) Neuro-physiological theories
The impulses to the brain normally travel through 2 pathways , namely
1) the relatively rapid lemniscal pathway through thalamus to sensory cortex and
2) the more slow extra-lemniscal pathway .
 36

It is believed that consciousness of the individual is maintained by the constant

traveling of impulses through the extra-lemniscal pathway .
The neuro-physical theory is based on the demonstration in 1952 of Larrabee
(quoted by Soma, 1971) that anaesthetics selectively inhibit transmission of impulses
through synapses and proposes that anaesthesia is brought about by the blocking of extra-
lemniscal pathway ( which is responsible for normal consciousness ) , without blocking
the lemniscal pathway .
It is however noted that the theory does not explain the mechanism as to how
exactly this selective blocking is brought about . Hence some authors have rather
humourously commented that this theory simply says that anaesthetics act by causing
anaesthesia.
6 ) Physical theories
Many investigators have tried to correlate the action of anaesthetic drugs to the
physical properties like solubility in fat / protein / water, and the thermo- dynamic
activity exhibited by vapour pressure / surface tension /intermolecular attraction /
molecular volume . But no satisfactory explanation is forthcoming regarding the
mechanism of production of anaesthesia , for which considerably more work seems
necessary .
STAGES OF GENERAL ANAESTHESIA
The development of complete general anaesthesia has been described in 4 stages .
Stage 1 : Stage of induction or the stage of voluntary excitement
The animal is fully conscious and is excited . The pulse and respiration rates are
accelerated . Breath holding may be noticed . Faeces and urine may be passed .
Stage 2 : Stage of involuntary excitement
Loss of Consciousness, regular respiration with breath-holding. Exaggerated
response to stimuli , violent limb movements or muscular rigidity may be noticed . This
is followed by gradual relaxation of muscles when the animal enters the next stage .
The stages 1 and 2 can be shortened and made to pass of smoothly by the use of
preanaesthetics .
Stage 3 : Stage of surgical anaesthesia. t is further subdivided into 3 planes .
 37

First plane of surgical anaesthesia ( light anaesthesia ): Breathing becomes regular and
the limb movements stop . The eyeballs may be moving from side to side but they soon
get fixed when the second plane of anaesthesia is entered . The palpebral , conjunctival ,
and corneal reflexes become sluggish or almost absent . In dogs and cats the pedal reflex
is present . ( The pedal reflex is the pulling away of the limb when the web of the foot is
pinched ). Minor operations like openings of abscesses can be done under light
anaesthesia .

Second plane of surgical anaesthesia ( medium anaesthesia ): The respirations are more
or less same as in the first plane but the pedal reflex becomes sluggish and muscular
relaxation becomes progressively more pronounced . In cattle , horse , pig and sheep the
eyeball is fixed and central but in the dog it may rotate downwards . Most operations
except laparotomy and thoracotomy , can be performed under medium anaesthesia .

Third plane of surgical anaesthesia ( deep anaesthesia ): Respiration rate is increased but
the depth of respiration is decreased . A pause between inspiration and expiration may
also be evident . the pedal reflex disappears . In the dog and cat the eyeball may once
again become central because of loss of tone of its muscles . There is generalized
muscular relaxation .
Some authors describe a fourth plane of surgical anaesthesia , but actually it is
nothing but the stage 4 of general anaesthesia .
Stage 4: Stage of medullary paralysis
Anaesthesia develops to this stage when there is over dosage and the
administration should be stopped immediately . The pulse becomes rapid . The eyeballs
appear dry and the pupil is dilated . The thoracic muscles are paralysed and during
inspiration the movements of the diaphragm causes bulging of the abdomen and inward
movement of the thorax . Since the movements of the diaphragm are jerky the respiration
is gasping in character . If proper counter measures are not taken at this stage the
respiration ceases and mucus membranes become cyanotic . Soon heart failure follows
and this is indicated by an ash grey colour of the mucous membranes .
 38

INJECTABLE ANAESTHETICS
The term intravenous anesthetic agents implies inducing anesthesia by drugs
administered intravenously.
Advantages of IV anesthesia
1. rapid and smooth induction of anesthesia,
2. little equipment requirement (syringes, needles, catheters),
3. easy administration of drugs.
Disadvantages include
1. difficult retrieval of drug once administered,
2.less control of depth and duration of anesthesia,
3. lack of ventilatory support,
4. poor tolerability in debilitated, dehydrated or toxicated animals.

PROPERTIES OF AN IDEAL INTRAVENOUS ANAESTHETIC AGENT

1. High therapeutic index
2. No toxic metabolites
3. Non-cummulative
4. Potent, so small volume is required for anesthetic induction/maintenance
5. Long shelf life and resistance to microbial contamination
6. Compatible with other dugs
7. Quick and smooth induction and recovery
8. Reversible with specific antagonist
9. Non-allergenic
10. No cardiopulmonary depression
11. Independent of liver and kidneys for metabolism and excretion
12. No effect on cerebral blood flow
13. No endocrinologic effect
14. No pain on injection
15. Inexpensive
 39

Drugs: Mechanism of action of barbiturates and non-barbiturates intravenous anesthetics

is believed to be via CNS depression by modulation of GABA-mediated
neurotransmission
1. Barbiturates
▼ Oxybarbiturate - pentobarbital and methohexital
▼ Thiobarbiturates - thiopental and thiamylal
2. Non-barbiturates:
▼ Chloral hydras, Propofol , Etomidate
▼ Alphaxalone , Propanidid
3. Dissociatives:
▼ Ketamine
▼ Tiletamine (in Telazol)
BARBITURATES:
Barbiturates are barbituric acid derivatives. Barbiturates with sedative-hypnotic
properties result from substitutions at the number 2 and 5 carbon atoms of barbituric acid.
 Substitutions determine hypnotic potency, lipid solubility, anticonvulsant
properties, onset, and duration of action
 Barbiturates that retain:
 An oxygen atom on number two carbon are designated as
oxybarbiturates. A sulfur atom on number two carbon results in
thiobarbiturates
They are classified into 4 groups according to duration of action
Long acting: ( 8 – 12 hrs ) Eg. Barbital, Phenobarbital
Intermediate acting: ( 2 – 6 hrs ) Eg. Amorbarbital, Butobarbital
Short acting: ( 45 min. to 1.5 hrs ) Eg. Pentobarbital, Secobarbital
Ultrashort acting: ( 5 –15 min.) Eg. Thiopental, Thiamylal.
For clinical anaesthesia, only ultrashort and short acting .drugs are employed.
Principal clinical uses of barbiturates:To induce hypnosis and anesthesia prior to or
supplement to other anesthetic agent or as sole agent for brief (15 min) operative
procedure. For clinical anaesthesia, only ultrashort and short acting drugs are employed.
• Treatment of increased intracranial pressure
 40

• used as anticonvulsant in status Epilepticus

• To supplement regional anesthesia or low potency agent such as nitrous oxide.
• As a narcosynthesis and narcoanalysis in psychiatric disorder
Features:
They depress the CNS by interference with passage of impulses to the cerebral cortex.
Barbiturates have been replaced by benzodiazepines for preanesthetic medication
Rapid onset of action of barbiturates renders these drugs useful for treatment of seizures,
but benzodiazepines are probably superior
Primary factors determining the plasma levels of the barbiturates are dose, concentration
and speed of administration, blood volume between injection site and brain, ionization ,
degree of protein binding, redistribution to non nervous tissue, and metabolism and
excretion of the drug and metabolites. Short acting barbiturates are destroyed principally
by liver. Major clinical properties include good hypnosis, poor to moderate analgesia
and dose-related respiratory and cardiovascular depression. There can be marked
recovery excitement, but this is reduced or removed by premedicationBarbiturates will
cross the placenta, and will affect the fetus Adult ruminants metabolize barbiturates faster
than do cats and dogs. Thus they may be shorter acting and less cumulative in ruminants.
Neonates do not have the necessary enzymes, and prolonged effect may be seen.
Although theoretically the horse also has the ability to metabolize barbiturates faster than
the dog, this is not so in the clinical circumstances, and recovery from cumulative doses
of barbiturates may be prolonged and violent.

Glucose Effect
It is reanaesthetizing action, which is observed in animals recovering from
barbiturate anaesthesia that are subsequently given glucose. Treatment of overdose of
barbiturates is IPPV to remove respiratory depression, and fluid therapy to increase renal
excretion.
DRUGS
NAME COMMERCIAL ROUTE ONSET DURATION DOSE
NAME (Sec) mg/kg BW
 41

SHORT ACTING BARBITURATES

Pentobarbital NEMBUTAL IV,IT,IP 30-60 1-2 Hr See the text

Secobarbital SECONAL IV

ULTRASHORT ACTING BARBITURATES

Hexobarbital EVIPAL IV 30-60 15-30 MIN

Thiopental sodium INTRAVAL IV 20-30 10-15

Dose : Horse and bovine – 6.0 – 10 mg/kg , 5 – 10 % solution
Ovine ,caprine and porcine – 6.6 – 11 mg/kg
Dogs and cats – 20 – 30 mg / kg as 1.25 – 2.5 % solution , slow IV

Thiamylal sodium ( SURITAL) IV

Dose – same as Thiopental sodium
Methohexital BREVITAL IV 10-30 5-15

Thialbarbitone KEMITHAL IV,IP,IT 20-30 15-45

Short acting: Pentobarbital (Saggital®, Nembutal®)

• No longer used routinely for anesthetic induction due to its prolonged rough
recovery.
• Pentobarbital is mainly used for seizure control in the animal.
• Intravenous dose for healthy unpremedicated dogs and cats is 20-30 mg/kg, given
to effect. It has a slower onset of action than thiopental (minutes).
• Pentobarbital is metabolized by the liver.
• In single stomached animals, full anesthetic doses produce about 1 hour surgical
anesthesia, but recovery takes up to 24 hours. Recovery is also violent (dogs howl
and paddle) unless premedication is used.
• Ruminants, however, recover quietly and very much faster, and the drug still has
a place to play in farm animal anesthesia.

Ultra-short acting barbiturates: Thiopental, Thiamylal, Methohexital

• Used for inducing general anesthesia in both small and large animals.
• In large animals, ultra-short acting barbiturates are usually used in combination
with glycerol guaiacolate (also called ‘guaifenesin’). When compared to using
ultra-short acting barbiturates alone, the total dose of ultra-short acting
barbiturates is decreased when it is given with guaifenesin. This results in less
cardiovascular depression and smoother inductions and recoveries from
anesthesia.
• It produce marked depression of respiratory centers and pronounced
hyperglycemia. It is rapidly redistributed ( muscle tissue ) and became localized
in body fat.
 42

Thiopental (Thiopentone) (Pentothal)

It is thioanalogue of pentobarbital sodium. The most widely used barbiturate. Thiopental,

5-ethyl-5-(1-methylbutyl)2-thiobarbituric acid . It produce marked depression of
respiratory centers and pronounced hyperglycemia. It is rapidly redistributed ( muscle
tissue ) and became localized in body fat. Available as white dry powder ( 500mg and 1
gm ) which has to be diluted with distilled water or NS. For small animals 1.25, 2.5, 5.0%
solution are used. Available as white dry powder ( 500mg and 1 gm ) which has to be
diluted with distilled water or NS.
It can be used as sole anaesthetic drug in dogs and cats @ 20-30 mg/kg b.wt.One
third of the estimated dose is injected rapidlywithin 15 sec. And the remainder is
administered slowly to effect. Additional doses may be administered to prolong the
anaesthesia when required. Route of administration may be IV,IP or IT. Bbecause of its
highly alkaline pH (= 11); perivascular injection will cause tissue necrosis.
Method of producing anaesthesia:
Weigh the animal, calculate the dose and draw excess solution into the
syringe.The first one third of solution is rapidly injected and watch the animal for the
following signs during induction
1. Licking of lips as if it is tasting the drug
2. Head moves from side to side
3. Loss of alertness in eyes
4. slowly animal relaxes
Signs of light state of anaesthesia
5. Dog will open the jaw, curl the tonguesimulating yawning
6. Palpebral reflex vanishes, But corneal and pedal present
7. Rolling of eye ball
Signs of Surgical anaesthesia
8. Pedal reflex got abolished
9. Rhythmic,shallow abdominal respiration
10.Abdominal muscle relaxation
11.Eye ball get fixed in the centre
 43

Now the animal has to be intubated. Further deepening of anaesthesia will lead to
respiratory collapse and death. Time required to render the patient unconscious is
generally 30-60 secs after administration. With no other drugs ,the anesthetic state
persists for 5-10 mins. Its concentration is low enough in the brain such that
consciousness returns. So is most commonly used in the induction phase of general
anesthesia.
As with all lipid soluble anesthetic drugs, the short duration of action of Sodium
thiopental is almost entirely due to its redistribution away from central circulation
towards muscle and fat tissue. Duration of action of highly lipid-soluble barbiturates
determined by redistribution. Metabolism of barbiturates principally involves hepatic
oxidation to inactive water-soluble metabolites, and approximately 10 to 15%of the drug
level metabolized per hour. Elimination half-time is 11.6 hrs.

NON BARBITURATES

1. Chloral hydras and its combinations – See Basal narcosis

2. Alphaxalone (Saffan)

Alphaxalone, a potent steroid anesthetic used in cats and non-human primates.

Dose: Cats – 9 mg/kg IV , 12-18 mg/kg I/M. Analgesia is fairly good. Quality of
anesthesia is good during deep anesthesia, but muscle twitching is seen at light level of
anesthesia, with convulsive type behavior in recovery.
• Major side effects are swollen ears and paws - this is very frequent although
variable in degree.
• Do not use in dogs!

3. Etomidate (Amidate ; Hypnomidate)

Etomidate is a carboxylated imidazole derivative. Etomidate is an intravenous, ultra-

short-acting, nonbarbiturate hypnotic drug. Widely used in man as an induction agent
and by continuous infusion.
Dose: Dogs and cats (2- 4 mg/kg).
It is the most expensive (vs propofol and thiopental)
 44

4. Metomidate ( HYPNODIL )
Hypnotic and muscle relaxant properties .

5. Propanidid (Epontol®)
Propanidid, a eugenol derivative, is highly water soluble and onset of induction and
recovery are rapid, the rapid recovery being due to both redistribution and metabolism.
This short acting intravenous induction agent
5. Propofol ( PROPOVAN ) : 2,6 Diiospropyl phenol

Propofol ( PROPOVAN ) (2, 6 diisopropylphenol)

Propofol is a non-barbiturate, non-dissociative intravenous anesthetic agent, and very

widely used in dogs and cats. It is a phenolic compound unrelated to any other general
anesthetics.

• Propofol is not water soluble, and is prepared as a milky white emulsion contains
no preservative and the emulsion supports bacterial growth and endotoxin
production. Once exposed to the air the contents in the vial must be used within 8
hours or discarded thereafter.
• Propofol is for intravenous use only (non irritant, but too rapidly metabolized for
other routes).
• Propofol is very respiratory depressant (worse than thiopental).
Water soluble , white coloured emulsion , containing propofol 10 mg/ml,
20 mg/ml solution

Dose – Horse – 2 mg/kg following premedication with xylazine .

Dog – 6-7 mg/kg IV as single bolus injection
Advantage – Recovery is very rapid than barbiturates but very expensive .
Disadvantage: Poor analgesic, Poor shelf life
INHALATION ANAESTHETICS
AGENTS IN CURRENT CLINICAL USE
Major use – Halothane and isoflurane
Minor use – Enflurane and Methoxyflurane and Nitrous oxide
New agents – Desflurane ( Suprane ) and sevoflurane ( Ultane )
Agents of historical interest – Chloroform, cyclopropane , diethyl ether , fluoroxene and
Trichloroethylene .
1) HALOTHANE ( FLUOTHANE )
 45

Clinical uses – Halothane is one of the most useful anaesthetic because it is non
inflammable , potent , non irritating , controllable and relatively nontoxic . It can be usd
in all species .
Dose – 2-4 % for induction and upto 5 % in large animals .
Maintenance – 0.5 – 1.5 %in small animals , 1-2 % in large animals .
2) ISOFLURANE ( FORANE , AARANE )
Clinical Use – Although a respiratory depressant , isoflurane is inert and non toxic
and produces minimal cardiovascular effects at surgical planes of anaesthesia . It is a
useful anaesthetic agent but expensive .It produces smooth induction and recovery period
in all species . It can be used with nitrous oxide.
Dose – Induction – 2.5 – 4.5 % which is facilitated by the use of a barbiturate or nitrous
oxide .
Maintenance – 1.0 – 3.0 %
3) METHOXYFLURANE ( METOFANE , PENTHRANE )
Clinical use – Since it produce good muscle relaxation , it can be used for many
minor surgical manipulations . It is the most potent anaesthetic , but the rate of onset of
anaesthesia and recovery is prolonged . Analgesia may continue into the recovery period .
If nitrous oxide is used , the amount of methoxyflurane can be reduced .
Dose – after barbiturate induction , 2-3 % is used to induce surgical anaesthesia
Maintenance – 0.2 – 1 %
4) ENFLURANE ( ETHRANE )
Clinical use – alternative to halothane or methoxyflurane because of good
analgesia and muscle relaxation . Rapid induction , recovery and low biodegradation . It
is compatible with nitrous oxide and relatively expensive .
Dose – induction with barbiturate is preferred with 4 – 6 % enflurane .
Maintenance – 1.0 – 3.0 % ventilation may have to be supported .
ANAESTHETIC DOSE
The term potency refers to the quantity of an inhalant anaesthetic that must be
administered to cause a desired effect . The anaesthetic potency of an inhaled anaesthetic
is inversely related to MAC . A very potent anaesthetic will have a very low MAC value .
The minimum alveolar concentration ( MAC ) is defined as the MAC of an anaesthetic at
 46

one atmosphere that produces immobility in 50 % of subjects exposed to a supramaximal

noxious stimulus .
MAC values of various anaesthetics for variety of species
SPECIES HALOTHANE ISOFLURANE ENFLURANE METHOXYFLURANE
Horse 0.88 1.31 2.12 0.28
Calf 0.76
Sheep 0.97 1.58 0.26
Dog 0.86 1.28 2.20 0.23

METHOD OF ADMINISTRATION OF INHALATION ANAESTHETICS

General features of anaesthetic apparatus for administration:
1. Source of Oxygen

2. Source of anaesthetic gas or Vapourizer

3. Patient breathing system

COMPONENTS OF BOYLE’S ANAESTHETIC APPARATUS

1. Oxygen cylinders: oxygen compressed at 2200 psi – cylinders are coloured Black
with white top
______________________________________________________________________
Type E G H
______________________________________________________________________
Wt.(kg) 5.9 50 59
Capacity (ltr) 660 5331 5570
_______________________________________________________________________
Amount of gas present in the cylinder can be calculated by psi x 0.3. The valve
bodies of E type cylinders attach directly to anaesthetic machine at the hanger yokes and
they utilize the pin index safety system to prevent interchange of oxygen and N 2O
cylinders.
 47

2. Pressure gauges: pressure gauge indicate the pressure on the cylinder side of the
regulator. The scale is graduated in kPa (Kilopascals) and psi. Bourdon tube type gauges
are commonly employed.
3. Regulators: It reduces the high and variable storage pressure to a lower and more
constant pressure that is appropriate for the machine. It maintains the constant flow to
flowmeter eventhough the pressure in the cylinder decreases as the contents are depleted.
(50 psi).
4. Flowmeters: They measures and indicates the rate of flow of gas and allows precise
control of O2 and N2O delivery to an out of system vapourizer and to the common gas
outlet They are known as rotameters. It consists of a vertically positioned glass tube
inside which a rotating bobbin is free to move up and down with a flow control valve.
The scale is ml/min. indicated by the top of the bobbin
Flow rate of Oxygen required:
I. For Induction
1. During Induction using Chamber – 5 litres/min
2. During Induction using Mask – 300 ml/kg/min or
1-3 ltr/min for animals weighing less than 10kg and
3-5 ltr/min for animals weighing more than 10 kg
3. During Induction using Endotracheal tube –200ml/kg/min
II. For maintenance of anaesthesia
1. Using nonrebreathing system: 130 -200 ml/kg/min.
2. Using total rebreathing system: 15ml/kg/min
3. Using partial rebreathing system: 25-50ml/kg/min
( A minimum of 500 ml/min should be allowed to the animal irrespective of the body wt.
and never use closed system for animals weighing less than 7 kg )
III. During recovery- 200 ml/kg/min.
5. Vapourizer: Except N2O, modern inhalant anaesthetics are delivered with vapourizers.
A vapourizer is designed to change a liquid anaesthetic into its vapour and to add a
specific amount of vapour to gases being delivered to the patient.
They are classified based on
1. Method of output regulation. Eg. Variable bypass vapourizer ( TEC)
 48

2. Method of Vapourization. Eg. Flow over, Bubble through, Injection types

3. Vapourizer location: In relation to the breathing system, the vapourizer may be
located either out of the system (VOC) or in the system (VIC).
VOC: Generally high potent and high volatile anaesthetics are administered with
VOC. They are called as precision vapourizers.
Eg. TEC vapourizer, FLUTEC Mark II, TEC Mark III.
VIC: Non precision vapourizers because of unpredictable outputs.
Eg. Ohio # 8 glass vapourizer, Stephens vapourizer
4. Temperature compensation: Heat is required to vaporize the liquid anaesthetics
which may be provided by
a) from vapourizer material itself
b) Electric heater or warm water jackets ( old type )
c) Electric heating device (TEC )
d) Thermostatic mechanism ( Bimetallic strip valve )
5. Agent specificity: a) Designed for particular inhalant anaesthetic
b) Multipurpose
6. Resistance to flow: a) High resistance (VOC)
b) Low resistance (VIC)
6. Common gas outlet: It is the site from which the gases that have passed through the
flowmeters and flush valve exit the anaesthetic machine on the way to the breathing
system. It is 15mm ID. The gas mixed with anaesthetic vapour is known as fresh gas.
7. Breathing system: Anaesthetic breathing system deliver anaesthetic gases and oxygen
to the patient, recover CO2 from the exhaled gases and usually provide a means to
manually support ventilation. In spontaneous breathing patients, BS should be able to
supply enough gases to meet the peak inspiratory demands of the patients at a pressure of
15 psi due to some resistance offered to the gaseous flow.
Classification:
1.Non rebreathing system: The expired gases are released to the atmosphere and cannot
be rebreathed.
2.Rebreathing system: Part or all exhaled gases after extraction of CO 2, flow back to the
patient
 49

Non rebreathing system: The fresh gas flow from the anaesthetic machine into a
reservoir from which the patient inhales and the exhaled gases are spilled, usually
through an expiratory valve to the atmosphere. CO2 removal depends on the fresh gas
flow rate and on the tidal volume of the respiration of the patient Commonly used NRS in
veterinary practice are variations of Mapleson’s system.
1. Magill ( Mapleson A ) system
2. T Piece ( Mapleson E) System
3. Co axial circuits (Variations of Mapleson A&D)System
1.Magill System: Most generally used one. It incorporates a wide reservoir bag, wide bore
corrugated tubing and a spring loaded expiratory valve. With this system rebreathing is
prevented by maintaining the total gas flow rate slightly in excess of the patient’s
respiratory minute volume. The animal inhales from the bag and the wide bore tubing;
the exhaled mixture passes back up the tubing displacing the gas in it back into the bag
until it is full. The exhaled gases never reach the bag because the capacity of the tube is
too great and once the bag is destended the build up of pressure inside the system causes
the expiratory valve to open, so that the terminal part of the expiration ( rich in CO 2 and
alveolar gas) passes out of the valve into atmosphere. During the pause which follows
expiration and before the next inspiration, fresh gas from the anaesthetic apparatus
sweeps the first part of the exhaled gas from the corrugated tube out through the
expiratory valve.
To ensure minimal rebreathing of the exhaled gases, the fresh gas flow rate should
be equal to or greater than the minute volume of respiration of the patient.

2.The T piece system: An open tube act as reservoir and there are no valves. The exhaled
gases are swept out of the open end of the reservoir tube by fresh gases flowing in from
the anaesthetic apparatus during the expiratory phase. Intermittent Positive Pressure
 50

Ventilation (IPPV) may be applied intermittently blocking the open end of the reservoir
tube, thus directing the fresh gas into the animal’s lung.
3.Co axial systems:
a) Bain syatem: Fresh gas passes up the central tube and the expired gas through the outer
sleeve. It is basically that of T piece system.

b) Lack circuit: Uses an alternative arrangement in which the fresh gas flows in the outer
sleeve and expiration through the inner tube. It is more satisfactory.

Rebreathing systems:
Principle: anaesthetic gases and vapours are largely exhaled from the body unchanged but
mixed with CO2. If this CO2 is removed and sufficient oxygen is added to satisfy the
metabolic requirements of the animal, the same gas or vapour can be rebreathed
continuously from the bag.
CO2 is usually removed by directing the exhaled mixture over the surface of
sodalime which is a mixture of 90% calcium hydroxide and 5% sodium hydroxide
together with 5% Silicate and water to prevent powdering. It is kept in a canister in
granular form( 4-8 mesh in size ) with an indicator dye (Ethyl violet) that changes
colour ( white to purple ) when CO2 absorbing capacity get exhausted.
There are two systems in use for CO2 absorption.
1. The To and fro system
2. The Circle system
 51

To and fro system : The canister is interposed between animal between animal and
rebreathing bag, fresh gases being fed into the system as close to the animal as possible to
effect changes in mixture rapidly.
Demerits: 1. Inspired gas gets heated up
2.Irritating dust may get inhaled from the sodalime

Circle System: This system incorporates an inspiratory and an expiratory tube with
unidirectional valves to ensure one way flow of gases; The rebreathing bag and sodalime
canister are placed between these tubes. The exhaled gases enter the ‘Y’ piece and flow
through the expiratory breathing tube and the expiratory one way valve. Gases may enter
the rebreathing bag before or after coursing through the canister. On inspiration gases
exit the rebreathing bag through inspiratory one way valve  inspiratory breathing tube
and the Y piece to the patient.

Components of circle system

1. Y piece: to connect endotracheal tube and inspiratory and expiratory breathing
tubes.
2. Breathing tubes: Made of rubber or plastic, flexible low resistant type. ID-22 mm
 52

3. Flutter valve: They are unidirectional valve, paired which direct gas flow away
from the patient on inspiration, preventing the rebreathing of exhaled gases before
they pass through the canister.
4. Fresh gas outlet
5. Pop off Valve:(Adjustable pressure limiting valve, Relief valve or Overflow
valve) : It vents gases to the scavenger system to prevent the build up of excessive
pressure within the circle and it allows rapid elimination of anaesthetic gases
from the circle when 100% oxygen is indicated.
6. Reservoir bag: Located on the absorber sideof the circle either upstreams or
downstreams from the canister.It is also used for controlled ventilation. Normal
size should be six times of patient’s tidal volume. It is available in 1, 2, 5, 15, 20
and 30 litres in capacity.
7. Manometer: Pressure gauge attached to the top of the absorber.
8. Air intake valve: (Negative pressure relief valve):It is located on the dome of the
inspiratory one way valve which will entrain room air in emergencies ie. In
absence of fresh gas flow. If fresh gas flow is interrupted, the valve allows
ampient air ( 21% Oxygen ) to enter the circle and prevents the patient from
inspiriting against a negative pressure and becoming hypoxic.

9. Vaporizer:
VOC
 53

VIC

10. Absorber: Contain sodalime or barolime

2NaOH + 2H2CO3 + Ca(OH)2  CaCO3 + Na2CO3 + 4H2O + Heat
11. Gas delivering system:
1. Anaesthetic free masks ( Malleable type )
2. Endotracheal tubes – Murphy type – cuffed ones
Different sizes of Endotracheal tube commonly employed
---------------------------------------------------------------------------
Animal Body.Wt. Internal Diameter
----------------------------------------------------------------------------
Cat 1, 3, 5 kg 3, 4, 5.5 mm
Dog 2, 4, 7, 9, 12 kg 5, 6, 7, 8 mm
12, 14, 16, 30, 40 kg 8, 10, 11, 12, 14, 16 mm
-----------------------------------------------------------------------------
12. Other Emergency provisions:
a) Flush valves: It delivers a high but unmetered flow of oxygen to the common
gas outlet or directly to the breathing system especially in case of emergency
b) Oxygen failure warning devices: It is a device to warn the anaesthetist that the
pressure of the oxygen supply is low by giving a whistling noise.
 54

DISSOCIATIVE ANAESTHESIA

This term is used to describe an anaesthetic state induced by drugs that interrupt
ascending transmission from the unconscious to conscious parts of brain , rather than by
generalized depression of all brain centers ie. dissociation between thalamus and limbic
system . It is characterized by complete analgesia, superficial sleep with cataleptoid
state.
Catalepsy: is defind as a characteristic akinetic state in which the extremities appear to be
paralysed by motor ane sensory failure without any impairment of consciousness. There
will be varying degrees of hypertonus and purposeful or reflexive skeletal muscle
movements. The animals may remain their eyes open and have good tone in the jaw
muscles with active laryngeal and pharyngeal reflexes.
Indications: Diagnosis and operative procedures where muscle relaxation not required.
The drugs employed are
1) Phencyclidine – 1st dissociative anaesthetic agent used for animal anaesthesia –
but not available nowadays .
2) Ketamine – ( Aneket, Ketmin ) 10 mg/ml, 20 mg/ml available as 2ml amp., 10 ml
vials. Route of administration – IV or IM.
It produce profound analgesia, tonic/ clonic spasm of limb muscles, No
relaxation, Hypersalivation. Since pharyngeal and laryngeal reflexes retained, It is
better to keep airway patent.
The rigidity of muscle is not dose dependant, which may be mistaken to indicate
an inadequate level of anaesthesia and the need for additional doses and unless this
possibility is recognized, overdoses may be given. To eliminate these side effects a
variety of other compounds like Atropine, Diazepam, Xylazine, thiobarbiturates or
inhalation anaesthetics are commonly given with ketamine
The difficulty inassessing the depth of unconsciousness with poor muscle
relaxation make it doubtful on its single use even on animals like sheep and cats. But it is
an agent of choice for sedation in reptiles and certain species of birds.
Dose: Horse: 2.2 mg/kg Body Wt. IV
 55

Goat:22-44 mg/kg Body Wt. IM or SC

Pig: 15-20 mg/kg Body Wt. IM or SC
Cat: 11-33 mg/kg Body Wt. IM or SC.
3) Tiletamine – only approved for use in combination with a benzadiazepine
derivative ( Zolazepam ) in a 1 : 1 ratio ( Telazol ).Use only in combination with
Xylazine or Detomidate
XYLAZINE-TELAZOL DETOMIDATE-TELAZOL ROUTE
SPECIES
Equine 1.1mg/kg – 1.65 mg/kg 20-40microgm/kg–1.1- IV
1.4mg/kg
Bovine 0.1mg/kg – 4.0 mg/kg IV

Dog 1.1 mg/kg – 8.8 mg/kg I/M

NEUROLEPTANALGESIA
The term neuroleptanalgesia has been used to describe the combination of opoids
with phenothiazines or buterophenons ( neuroleptics ). They have the specific property of
reducing opoid induced vomiting in dogs. Neuroleptic techniques can be used in two
ways. A comparatively low opoid dose rates they can be used for controlling the animals,
or as premedication before GA. At higher dosesthey can be used to produce sufficient
depression of the CNS to enable surgery to be performed ( Neuroleptanaesthesia ). It is
associated with profound respiratory depression.
Eg.1. Mixture of Fentanyl 0.05 mg/ml and Droperidol 20 mg/ml (Thalamonal)
2. Mixture of Fentanyl 0.315 mg/ml and Fluanisone 10 mg/ml (Hypnorm )
3. Mixture of Fentanyl and Butyrophenone
4. Mixture of Etophine 0.074 mg/ml & Methotrimeprazine 18 mg/ml (Immobilon SA )
5. Mixture of etorphine 2.45 mg/ml and Acepromazine 10 mg/ml (Immobilon LA )
The result obtained by neuroleptanalgesic techniques are more impressive in
monkeys. It provide more advantages over other conventional methods of anaesthesia
especially when skilled assistance is not available.
INTRAVENOUS REGIONAL ANALGESIA ( IVRA )
It is a rapid and reliable method for producing short term ( < 2 hours )
anaesthesiaof the extremities . Mode of action of this technique is not clear but seems to
 56

be both safe and simple for operations on the digit in dogs and bovines which are unfit
for GA .
Technique :
A small needle or catheter is inserted into a vein at the distal extremity of the limb
. A torniquet ( rubber ) is applied sufficiently above the site of operation . The limb is
desanguinated by wrapping it with an esmarch bandage . After removing this bandage ,
2% solution of LH is injected IV with light pressure ( 30ml in cattle and @ 2.5-5 mg/kg
in dogs ) . 5- 10 mins are required to achieve maximum anaesthesia and remains for 30
mins to 1 hour . Once the torniquet is removed , sensation returns within 5 – 15 min .

ELECTROANAESTHESIA
This is a method of production of narcosis by employing direct , pulsating or
alternate current activating either opioid or nonopioid pain control pathways or both in
brain . It is of greatest use in situations where prolonged anaesthesia is required for
experimental purposes . Electronarcosis is characterized by convulsions on induction ,
profuse salivation , hyperthermia , severe stress , sharp rise in blood pressure . Use of
muscle relaxant and atropinization of the animal is necessary before induction . It is very
difficult to assess the depth of unconsciousness achieved . Muscle relaxation varies from
adequate to poor . The photomotor reflex is probably the best means of determining the
depth of anaesthesia . Even though it is advocated for restraint of food animals , it cannot
be recommended as a humane method of restraint .

HYPOTHERMIA
As body temperature of warm blooded animals falls, metabolism is reduced and
the need for oxygen is also reduced. Heart, brain, liver or other vital organs can survive at
a low temperature for a considerably increased period when deprived of all or a portion
of their blood supply
Effects: It decrease anaesthetic requirements (MAC) of inhalation anaesthetics. It produce
shivering which has to be prevented by deep anaesthesia with tranquilizer. Since it is a
form of GA, It cause profound vital organ and CNS depression, Hypotension, increased
clotting time.
 57

Indications: In surgery of heart, great vessels, Brain, Spinal cord, removal heart worms
in dogs. Employed in anaesthesia of reptiles and amphibians by refrigeration at 5 0 C for 2
hrs, immersion in ice water normally supplemented with LA.
Methods of whole body cooling:
1. Surface- Keeping the body over a bed of iceor in ice water
2. Body Cavity-Pouring cold saline solution into the open thoracic cavity.
3. Extracorporeal cooling – Running blood from a cannulated artery through
a heat exchanger using cold tap water as cooling medium.

ACUPUNCTURE

This technique involves insertion of specially designed needles at specific points

and their stimulations by various means to produce analgesia or to cure certain diseases .
These points are known as acupuncture points .
The procedure is safe , no post anaesthetic complication and can be used in poor
surgical risk cases . Major disadvantage is poor muscle relaxation . It has been used in
cattle , buffaloes , sheep and goat and dogs to produce local anaesthesia for surgery and
as a therapy for various medical and surgical disorders .
An alphanumeric code system is derived for naming the points L ,BL , LI ,ST etc.
An imaginary line connecting different points specific to an organ is known as meridian .
There are more than 360 points in body and 12 organ meridians .
Technique
Needling at appropriate points and stimulation of the needles form the basis of
acupuncture . Stainless steel solid , filiform shafted needles with silver or silver plated
spirally wound handle are most commonly recommended . Various methods have been
used to provide stimulus for acupuncture and include mechanical , thermal , chemical ,
electronic and light stimulation . Mechanical and electronic stimulation are most
commonly used .
For needling the needles are twisted with the thumb and index finger in a lift
thrust form and rotation movements which should be made rhythmically at a steady
frequency of 100-200 per minute .
 58

For electronic stimulation , a transistorized electro acupuncture unit capable of

delivering biphasic square , biphasic spike and dense disperse wave forms of pulses with
a frequency range of 0-323 Hz along with a pulse width of 2.2 mm is used . Generally the
current of 35-100 mA and a frequency of 120-200 Hz is sufficient stimulation of
acupoints .
Moderate muscle relaxation and analgesia develops normally within 20-30
minutes after onset of stimulations . All aseptic technique has to be taken while inserting
needles and in pregnancy certain points leading to abortion has to be prevented .
ANAESTHESIA OF LABORATORY ANIMALS

Preparation of the animals: Fasting for 1-2 hrs. Weigh the animal followed by physical
examination. Preoperative hypothermia has to be taken care of
Rodents:
1. Injectable anaesthetics: Barbiturates, Dissociation,Neurolept etc.
Route of administration: IM at thigh, IV through lateral tail vein and Intraperitoneal
through lower left quadrant of abdomen
2. Inhalation: induced by keeping in the chamber and maintained by face mask using CO 2
50-70% mixed with oxygen in mice.
Rabbits: They should be handled carefully to avoid self injury like fracture, paralysis etc.
1. Injectable anaesthetics: Sedatives, Barbiturates, Dissociation, Neurolept etc
Route : IM at thigh muscle or lumbar region, IV through lateral ear vein
Primates: Important problem is restraining the animals during induction. Nets, squeeze
cages etc. can be employed.
Injectable anaesthetics: Ketamine @ 10-15mg / kg IM for induction followed by
Telazol @ 15 mg/kg or halothane / Isoflurane for inhalation are widely employed.
Other drugs of choice are Droperidol and Fentanyl, Etorphine or Acepromazine.

Common drugs and their dosages

MICE RAT GUINEA PIG HAMSTER RABBIT PRIMATES
Thiopental 25-50 20-40 15-30 IV
( mg/kg) IV IV

Propofol 12-26 7.5- 10 7.5-15 IV

( mg/kg) IV IV
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Ketamine 80-100 50-100 40 – 200 IM 40-80 IP 20-60 IM 8-10 IM

( mg/kg) IM IM

Xylazine 2.5 IM -- 3-9 IM,IV

( mg/kg)

Telazol 80-100 20-40 10 – 80 IP 50-80 IP 30-64 IM 2-6 IM

( mg/kg) IP IP

Innovar vet 0.001- 0.02- 0.44–0.88 0.15ml/100g 0.125 ml /

0.01ml/g 0.6ml/1 ml/kg IM IP kg SC
IM 00g IP
10%soln
ANAESTHESIA OF WILD AND CAPTIVE ANIMALS

Chemical immobilization
Indications: Marking, Sampling,Translocation,Medical treatment and research.
General considerations:
To be done only if needed, Safety of the drug, knowledge about the animal behaviour,
experience in handling the equipments are necessary. These procedures generally lack
enough preparation, use of preanaesthetics, sufficient knowledge regarding the status of
the animal whether pregnant, undernourished or with parasitic infestation etc.
Instrumentaion:
1.Blow Gun : It is a simple form of RDD ( Remote Drug Delivery System ). 1-2 meter
long pipe is used to propel light weight drug dart for a distance of 10-15 mts.
2.Power Projection System: Rifles and pistols using CO2 gas or compressed air.
3.Dart with explosive discharge mechanism.

ANIMAL MEDETOMIDINE KETAMINE ETORPHINE ACEPROMAZINE

(microgram / kg ) ( mg/kg) ( mg / animal ) ( mg/animal)
Primates 50-100 3-5
Rodents 100-300 5.0
Carnivora 60-100 2.5 – 5.0
Deer 70-100 1-2
Tiger 7 – 14
Lion 10-20
Bison 2-2.5
Black buck 0.5
Elephant 5-8 40-60
Hippo 2-3 40
Camel 2 mg/ lb BW
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Bear 0.5-1.0
Crocodile 0.05-2.0

BIRDS AND SNAKES

BIRDS KETAMINE XYLAZINE PENTOBARBITAL TELAZOL
mg/lbBW mg/lb BW
Parakeet 0.1-0.2mg/kgBW IM 50-70 IM 0.3-0.5mg/g BW IM 15-30 IM

Parrot 0.1-0.2mg/kgBW IM 50-70 IM 0.3-0.5mg/g BW IM 15-30 IM

Pigeon 0.02-0.1mg/gBW IM 50-70 IM 0.3-0.5mg/g BW IM 15-30 IM

Chicken 0.02-0.05mg/gBW IM 50-70 IM 0.3-0.5mg/g BW IM 15-30 IM

Duck 0.02-0.05mg/gBW IM 50-70 IM 0.3-0.5mg/g BW IM 15-30 IM

Snake 25-50 mg/lb BW IM not 10-15mg/lb BW 5-20 IM

recommended IP or IM

MONITORING THE ANAESTHETIZED PATIENT

. The purpose of monitoring is to provide information that can be used to maximize
the safety of anaesthesia and minimize the decrement of organ function , thereby
improving the likelihood of an uneventful recovery .
1) Monitoring begins in the preoperative period , where the patient is assessed to
determine the existence of any abnormal processes . The magnitude of pathology and its
influence on the patients response to anaesthesia and the surgical procedure are
estimated. This evaluation provides the basis for drug selection , methodology of
monitoring and the support to the specific needs of the patient .
2) Once the animal is anaesthetized – the 1st step to be assessed is the depth of
anaesthesia which may vary depending on the type of drug , its characteristics in
production of various symptoms , species wise response and the pathology . The
physiological consequences of the anaesthetized state has to be evaluated through
monitoring . It may indicate the function of the organ system .
3 ) Pulmonary monitoring :
a) Breathing rate , rhythm , nature and effort .
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b) Ventilometry – Anaesthesia ventilator is a reservoir bag in a closed container that can

substitute for the reservoir bag of an anaesthesia breathing system . It gives the volume of
air and rate of respiration .
c) Blood gas analysis – By blood gas analyzer. PaO2 and PaCO2 are indicative of
pulmonary function .
PaO2 – oxygenating efficiency of lungs .
PaCO2 – ventilatory status of the patient .
d) Pulse oxymetry – By using pulse oxymeters attached to the patient externally ( to
tongue / tips / tail or toe nail ) – it measures the pulse rate and Hb saturation .
4) Cardiovascular monitoring : Electrical activity by ECG – indicate brachycardia ,
tachycardia and arrythmias , blocks etc .
a) Blood pressure – indicate peripheral perfusion – product of COP , vascular capacity
and blood volume – Sphigmomanometer is used.
b) CVP – It is the luminal pressure of the intrathoracic venacava . It is the measure of the
relative ability of the heart to pump the venous return – can be assessed using water
manometer .
5) Renal function :
Urine output – indirect measure of renal blood flow . Normal is 1-2 ml / kg BW.
6 ) Lab evaluations : PCV, Hb, Total proteins / albumin and Platelets / coagulation
parameters
ANAESTHETIC EMERGENCIES AND ACCIDENTS
Induction of GA will often decrease cardiac output , blood pressure , affect the
peripheral perfusion , decrease alveolar ventilation , interfere with temperature regulation
and increase intracranial pressure . In most of the cases stress of the surgical
manipulation may worsen the condition and lead to anaesthetic emergencies .

I ) RESPIRATORY SYSTEM EMERGENCIES

1) Hypoxia – Apnea and airway obstruction leading to hypoxia commonly occur during
induction of anaesthesia . Airway obstruction may be due to
Tongue or epiglottis coming in contact with the base of the tongue .
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In brachycephalic dogs , ventral border of the soft palate may come in contact with
the base of the tongue .
Large blood clots in larynx.
Impaction of epiglottis .
Laryngeal and bronchial spasm .
Correct the positioning of the animal and make the airway straight and patent , fix
the endotracheal tube in position and provide oxygen enriched environment .
2 ) Aspiration of material from the oesophagus and stomach :
It can happen due to vomiting or passive regurgitation . It may lead to respiratory
obstruction accompanied by bronchospasm and inhalation pneumonia in later phase . The
following measures can be taken .
a) Providing cuffed endotracheal tube .
b) Proper fasting and decompression of stomach through stomach tube .
c) Thorough aspiration of tracheobronchial tree and provision for O2 .
d) Postoperative antibiotic therapy .

3 ) Respiratory insufficiency : May be due to

a) Administration of opioids and other sedatives .
b) Overdose of induction agent .
c) Positioning of patient .
d) Respiratory effects of inhalant .
e) Surgical trauma .
f) Excessive use of opioids during recovery .
Treatment :
a) Provision for O2 .
b) Tracheostomy
c) Ventilation – drug to stimulate ventilation like Doxapram HCl @ 1-4 mg/kg IV
and Methetharimide @ 0.4 – 0.8 mg/kg IV can be tried .
II ) CARDIOVASCULAR EMERGENCIES
A) Haemorrhage –
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Not much life threatening . But the blood escapes from natural orifices or acute
loss of blood which is accumulated in the body cavities can cause shock .
Treatment :
Administration of fluids ( LRS ) @ 40 – 90 ml / kg IV / hr .
Blood @ 20 – 40 ml / kg IV
B ) Cardiac Dysrhythmias –
May occur as a result of preexisting medical conditions , administration of
premedicaments , anaesthesia induction and maintenance agents and surgical stimulation.
1) Tachycardia – LRS @ 10 – 20 ml /kg / hr .
Propranolol @ 0.05 – 0.1 mg / kg IV and increase anaesthesia.
2 ) Bradycardia – Atropine @ 0.02 mg / kg IV, Glycopyrolate @ 0.005 mg / kg IV
3 ) Ventricular dysarhythmias – Dogs – Lidocaine 0.5 mg / kg IV
Cats – 0.2 mg / kg IV
C ) Cardiac arrest –
1) Chest compression - @ 60 / min in dogs.
30 compressions / min in adult horses / cattle .
2) Electrical defibrillation – For defibrillation through an intact chest wall good electric
contact should be assured by conducting gel .
Shocks of about 1 J is for cats .
1 – 8 J for dogs
400 J in horses and cattle .
Repeated shocks at 15 secs interval .
3 ) If both the above methods fail – direct compression of the heart through thoracotomy
can be done under intermittent positive pressure ventilation .
4 ) Hypotension – LRS – 10-20 ml / kg IV AND dopamine –3-5 microgm/kg/min.
III ) TEMPERATURE MONITORING
Hypothermia – warmed fluids – 5 – 10 ml / kg IV / hr .
Water heating pad
Hyperthermia – generally with for circle system or to and fro system.
stop anaesthetic administration and prvide Oxygen,Fluids and
tranquilizers. .
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Malignant hyperthermia – a feature in pigs which are halothane sensitive and is

transient
IV) HYPOGLYCEMIA – Administer Dextrose 5% - 1-2 ml /kg IV
V) METABOLIC ACIDOSIS – Administer Soda bicarbonate – 1-2 mEq / kg IV
every 10 mins .
VI) ANAPHYLAXIS : Reaction may be acute or delayed, characterised by oedema,
hypotension, reduced tissue perfusion, cardiac arrest.
Treatment: Oxygen administration, Cardiac resuscitation, Epinephrine @
1 microgm/kg/min. IV, Methyl prednisolone@ 1 mg/kg IM may be administered.
VII) PROLONGED RECOVARY–
Reversal of opoid analgesic effects:Nalaxone – 0.0032-0.01 mg/kg iv or im
Reversal of Benzodiazepine effects: Flumazenil – 0.2 – 5.0 mg/kg iv
Reversal of Peripheral muscle relaxant effects:
1. Neostigmine (Myostigmin, Telstigmin) - 0.011 mg/kg Slow i.v.
Atropine sulphate @ 0.01 mg/kg may be given concurrently to counteract the
muscarine effect of increased acetyl choline like bradycardia,hypotension,
salivation etc
2. Edrophonium ( Enlen ) – 0.5-1mg./kg i.v.
3. Pyridostigmine
Reversal of barbiturate effects: Doxapram – 1-2 mg / kg IV
Alpha2 Adrenergic antagonists: They have to be administered before recovary
1. Yohimbine ( Yobine ) – Dog: 100-150 microgm / kg IV
Cat: 100-200 microgm / kg IV
Horse: 75-150 microgm / kg IV
Cattle: 100-200 microgm / kg IV

2. Tolazoline ( Priscoline )

3. Atipamizole ( Antisedan )

VIII) POSTOPERATIVE PAIN – Administer Morphine , bupremorphine etc.

IX) ACCIDENTS ASSOCIATED WITH POSTURE – Anaesthetized animals should
be hamdled carefully. Accidents include: Disc protrusion,Joint problems, Obturator
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paralysis, Corneal injuries, Facial paralysis, Aspiration pneumonia, Paraplegia, injuries

associated with induction/recovery.
X) ANAESTHETIC EXPLOSIONS AND FIRES –explosion may occur from static
electricity with use of explosive inhalation agents, use of diathermy, alcoholic skin
disinfectants.
XI) COMPLICATIONS ASSOCITED WITH DRUGS –
1. Intravenous injection of irritant anaesthetics: Phlebitis , cellulitis ( Dilute the site with
large volume of saline mixed with hyaluronidase).
2. Local anaesthetics: They both stimulate and depress the activity of CNS. There may be
cortical stimulation followed by respiratory and vasomotor depression causing fall in
BP, respiratory failure.
Treament: IPPV, control convulsions,administer ultrashort acting barbiturates,
vasopressor drugs to prevent hypotesion.
3. Epidural analgesia: Drugs may cause reaction affecting both the meninges and spinal
cord end up with myelitis and neuritis.
XII) DANGERS TO ANAESTHETISTS AND POLLUTION – Toxicity due to drugs
absorbed through skin, Inhalation of anaesthetics.

ANAESTHETIC PROCEDURES AND TECHNIQUES IN HORSES

I. General considerations:
1. Preparation-
a) Fasting ( food for 8-12 hrs and water for 2 hrs )
b) All the shoes should be removed
c) Groomed, wiped with moist cloth
d) Preparation of the site
e) Weight recording, preanaesthetic evaluation sp. Cardiopulmonary system
f) Administration of preanaesthetic 20-30 min. prior to induction
2. Stabilize acid-base disturbances
3. Proper positioning and appropriate padding of body parts
4. Facility for Assisted/controlled respiration
5. Monitoring facilities Eg.BP
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II. Common preanesthetic medicatioins:

1. Acepromazine
2. Promazine
3. Xylazine
4. Chloral hydrate
III. General anaesthetic techniques:

1. Collect necessary equipment

a) Endotracheal tubes 300,500,750,1000 & above Kg.b.wt(16,20,25,30,40mm) by
nasotracheal, orotracheal or tracheotomy method
b) I/v catheters, proper padding materials, monitoring equipments
c) Pressure in the tank – Oxygen(2,500 psi), Nitrous oxide (750psi)
d) Oxygen flow rate-Induction:17-22ml/kg/min
Maintenance: 4-13ml/kg/min.
IV. Anaesthetic Induction agents:
1. Thiamylal sodium alone or in combination with guaiafenesin
2. Guaiafenesin
3. Ketamine 0.7-1.0mg/Ib i.v
4. Halothane 3-5% concentration
V. Inhalation anaesthesia
1. Halothane – 1-3%
2. Enflurane – 1-3%
3. Isoflurane – 1-3%
Inhalation anaesthesia is preferred over intravenous in cases for more than 45mts
of anaesthesia is required and for horses that have CV and respiratory compromise.
Monitoring includes evaluation of eye refelexes and cardiopulmonary function. They are
administered via circle or to and fro absorption system using VOC vapourizer.(Eg. VET
TEC MODEL LAVC 2000). Recovary is acritical phase of equine anaesthesia, but in
many ways least controllable. Smooth recobery are facilitated by placing the horse in a
quiet and darkened enviorment with good footing.
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ANAESTHETIC PROCEDURES AND TECHNIQUES IN RUMINANTS

I. General considerations:
1. Preparation- Most important part in decreasing the risk of regurgitation is to decrease
rumen pressure prior to anaesthesia by
a)Fasting ( food for 24-36 hrs and water for 8-12 hrs in large ruminants )
food for 12-24 hrs and water for 8-12 hrs in small animals)
2. In Cattle, most of the surgical techniques can be performed using local/regional
anaesthesia
3. GA is advised when other techniques are not adequate
4. Regurgitation is caused by vagal effect on reticular contractions and parasympathetic
effects on pharyngoesophageal and gastroesophageal sphinctors. Anaesthetics drugs
increase the risk of regurgitation by
a) relaxing the pharyngoesophageal sphinctor
b) Relaxing the gastroesophageal sphinctor
c) Depressing the swallow reflex
Prolong recumbancy also increases the risk of regurgitation
II. Common preanesthetic medicatioins:
1. Acepromazine
2. Xylazine
3. Telazol
III. General anaesthetic techniques:
1. Collect necessary equipment
a) Endotracheal tubes 10, 30, 60, 100, 300, 600, 1000 & above Kg.b.wt (6, 8, 10, 15,
20 & 25 mm) through dental speculum and mouth gag or laryngoscope
b) Oxygen flow rate- Induction: 9-18 ml/kg/min.
Maintanance: 8-13 ml/kg/min.
IV. Anaesthetic Induction agents:
a. Thiopental sodium and Thiamylal sodium
b. Pentobarbital sodium
c. Guaiafenesin
d. Xylazine - Ketamine combination
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e. Xylazine - Ketamine – guaiafenesin combination

f. Telazol
V. Inhalation anaesthesia
1. Halothane – 0.5-2%
2.Isoflurane – 1-2%
Inhalation anaesthesia is preferred over intravenous in cases for more than 45mts
of anaesthesia is required on debilitated animals. Small ruminants weighing less than 50-
100 kg can be induced by mask. Large animals are induced by IV or IM anaesthesia. The
inhalants are administered by low flow methods with a precision vapourizer and CO 2
absorption.

ANAESTHETIC PROCEDURES AND TECHNIQUES IN DOGS

I. General considerations: A variety of anaesthetic procedures and techniques can be used
to safely produce chemical restraint and anaesthesia in dogs
1. Preparation-
a) Fasting ( food for 6-12 hrs and water for 6 hrs )
b) Weight recording,preanaesthetic evaluation
c) Administration of preanaesthetic 10-20 min. prior to induction
2. Stabilize acid-base disturbances
3. Proper positioning and appropriate padding of body parts
4. Facility for Assisted/controlled respiration
5. Monitoring facilities Eg.BP

II. Anaesthesia for less than 15 min.

1. Sedatives and tranquilizers(Diazepam, xylazine, Meditomidine)
2. Opoids and Neroleptanalgesics ( Butorphanol, Xylazine, Acepromazine-
Butorphanol combination)
3. Cyclohexamine and combinations ( Xylazine-Ketamine, Telazol )
4. Thiopental sodium or propafol
III. Anaesthesia for 15 min. to 1 hr. ( Inhalation anaesthesia )
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1. Premedication: Sedatives, Tranquilizers and other injectable drugs according

to the drug of choice for GA
2. Induction: Thiopental sodium, Xylazine-Ketamine, Xylazine-Midazolam,
Propafol
3. Maintanance:
Agent Induction Maintanance
1. isoflurane 3-4% 1.5-3%
2. halothane 3% 1-2%
3. Methoxyflurane 3% 0.5-1.5%
4. Enflurane 4-5% 2.5-4%
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