29.

LABOUR ANALGESIA

The pain of childbirth is often rated by women as being the most painful experience of their
lives. As each woman's experience of labour pain is unique, analgesic options must
therefore be varied. 

Relieving Labour Pain

Labour pain has both visceral and somatic components. The first stage of labour involves
uterine contractions, and cervical dilatation and effacement. This causes autonomically
mediated pain, which is poorly localised and often referred to the back, abdomen and upper
thighs. The nerve impulses are transmitted to the spinal cord via visceral afferents (C and A-
delta fibres) entering from T10 to L1 spinal segments. Neuraxial opioids are effective for
visceral pain. The second stage of labour is defined as the period after complete cervical
dilatation until delivery of the foetus. The pain of the second stage is due to stretching of
the vagina and perineum and is somatic. It is better localised and is transmitted via the
pudendal nerves to the spinal cord (S2 to S4).

Ideal labour analgesia should be effective, safe for mother and foetus or newborn, and have
minimal effects on the progress of labour. Options for relief of labour pain range from the
non-pharmacological to systemic opioids or regional anaesthesia.
Non-pharmacological methods include psychological preparation of the parturient and her
partner, having a support person present throughout labour, positioning and movement,
relaxation and breathing techniques, massage, heat and cold, imagery, hypnosis, music,
sterile water injections and transcutaneous electrical nerve stimulation (TENS).

Relaxation and Breathing Technique

The term “psychoprophylaxis” means to prevent pain through psychological methods and
requires a combination of antenatal instruction and the use of coping methods during
labour. The expectant mother is taught to respond to the beginning of a contraction by
immediately taking a deep “cleansing breath”, gently exhaling, and then breathing in a
shallow pattern until the contraction ends as well as focusing on a specific object. 

Positioning and Movement

Pain relief requirements may be decreased again by up to 30% if the mother is mobile
during labour. Changing to a more comfortable position may be of great benefit as long as
lying flat on the back (aorto-caval compression) is avoided.

Heat, Cold Showering and Massage

Are all harmless techniques that may provide additional comfort.

Hypnosis
Hypnosis may reduce the overall use of pain medication during labour but does not seem to
reduce the use of epidurals. 

Acupuncture

There is very limited evidence that acupuncture might reduce the need for other forms of
pain relief.

Transcutaneous Electrical Nerve Stimulation (TENS)

The gate theory of pain proposes that stimulation of large myelinated A-ß nerve fibres will
close the gate (i.e. increase the pain modulating function of the substantia gelatinosa). Pain
sensation from A-delta and C nerve fibres may thus be altered or blocked. TENS is thought
to affect A-ß fibres (although others suggest that the endogenous opioid system is
responsible for TENS). Some women find TENS helpful during the early stages of labour.

Intradermal Sterile water injections

Injecting four to six intradermal injections of water, administered in  the lumbar region, can
be used to temporarily relieve back  pain that does not resolve between contractions. This
technique is only effective in relieving back pain and not contraction pain. The injection sites
are at the posterior superior iliac spines (PSIS) and 3 cm below and 1 cm medial to the PSIS
bilaterally. The exact anatomical location is not critical to success. Ideally bilateral injections
are performed simultaneously,  with 0.1 - 0.3mls intradermally, raising a visible bleb
approximately 0.5 cm in diameter. The technique may be repeated every 30 minutes.

Nitrous Oxide

Nitrous oxide is an analgesic.  The side-effects include a feeling of disorientation or

confusion and possibly nausea. It has no side effects on the foetus, does not interfere with
uterine contractions and has no adverse effects on the normal physiology and progress of
labour. Unfortunately, it is difficult to time effectively when in labour and so about 30% of
women have no relief from nitrous oxide. To achieve its peak analgesic effects, it is
necessary to start breathing nitrous oxide 45 seconds before a contraction, which is very
difficult to time. Its onset of action is 15 seconds and the elimination is rapid as it is not very
soluble in blood. A concentration of 50% is required to produce worthwhile analgesia.

Opioids

Opioids have the advantages of ease of administration, wide availability, lower cost, and are
less invasive than neuraxial techniques, however substantial relief of labour pain is generally
not achieved. Adverse effects of all opioids include drowsiness, hypoventilation, urinary
retention, nausea/vomiting and delayed gastric emptying. Opioids cross the placenta by
passive diffusion and some are trapped by ionisation. They will often produce a prolonged
‘sleep phase’ pattern on cardiotocography, with a reduction in foetal heart rate variability,
accelerations and decelerations. Pethidine provides variable pain relief in labour; much of its
effect is due to sedation rather than analgesia. Morphine is preferred to pethidine due to its
reduced half-life in both mother and newborn and  its metabolites do not have convulsant
effects. Opioids should not be administered during the late  second stage of labour because
of its respiratory depressant effects on the baby. If an intravenous or intramuscular opioid is
used, an antiemetic should also be administered.
Patient-controlled analgesia opioids have also been used with mothers typically receiving a 
10 to 25 µg bolus of fentanyl with a 5-minute lockout and no background infusion. 
Remifentanil has a rapid onset of effect of approximately 1 min. It is degraded by non-
specific tissue and plasma esterases, and does not accumulate, with a context-sensitive half-
time of approximately 3 min. Remifentanil PCA may be an alternative for epidural analgesia
in cases where the woman cannot or does not want to receive epidural anaesthesia,
however there is concern for its safety as remifentanil is associated with maternal
respiratory depression.

Epidural Analgesia

Classic epidural analgesia involves placement of a catheter in the epidural space with
administration of an initial bolus dose followed by repeated boluses or an infusion of a local
anaesthetic agent with an opioid. Epidural anaesthesia can provide complete analgesia for
labour and delivery as well as for caesarean section; however, epidural anaesthesia requires
a greater level of skill for the anaesthesia provider and nursing staff. 

Combined Spinal Epidural Analgesia (CSE)

CSE involves a single injection of local anaesthetic and/or opioid into the subarachnoid
space and the insertion of an epidural catheter, with the use of the epidural as per usual. It
combines the rapid, reliable onset of profound analgesia resulting from spinal injection with
the flexibility and longer duration of epidural techniques. 
The indications for a combined spinal epidural include:
 very early labour in women who wish to ambulate
 late in labour for multiparous women
 operative or instrumental delivery where epidural analgesia is indicated
postoperatively.

Patient Controlled Epidural Analgesia (PCEA)

PCEA was introduced so that labouring women could control the dose of epidural
medication according to their need as their  labour and pain patterns changed. Boluses of
the epidural mixture are delivered on patient demand with a lockout interval of 10 to 20
minutes.

Single shot spinal

Access to epidural analgesia for labouring women in many countries can be challenging. The
single shot spinal technique has been shown to provide reliable analgesia for labour, but the
duration of analgesia is limited because no catheter is placed for a continuous infusion. The
low-dose combination of 0.5% hyperbaric bupivacaine 2.5 mg (0.5 mL) and fentanyl 25 μg
(0.5 mL), volume made to 1.5 mL with normal saline,  provides up to 2 - 3 hours of
ambulatory pain control. Common complications include pruritus and shivering, however as
sympathectomy is limited to sacral nerves, hypotension rarely occurs. Ideal candidates for
single injection spinal analgesia are parous and have advanced cervical dilation. 

Ketamine

With rapid onset, potent analgesia and a favourable cardiopulmonary profile, Ketamine was
widely used in obstetric anaesthesia and labour analgesia before neuraxial
analgesia/anaesthesia became safe and effective. The potential neuroprotection and
neurotoxicity of ketamine on the newborn is currently inconclusive. A distinctive feature of
ketamine is its potent analgesic effect produced at subanesthetic concentrations.
Continuous infusion of ketamine with a slow loading dose of 0.2 mg/kg at the onset of
labour pain, followed by an infusion of 0.1- 0.2 mg/kg/h 30 minutes later, until delivery,
provides significant pain relief without significant maternal, foetal or labour complications.
Ketamine may also be used as rescue analgesia for inadequate neuraxial anaesthesia during
caesarean delivery (5-10 mg or 0.2 to 0.4 mg/kg increments).

EPIDURAL ANAESTHESIA FOR LABOUR

Epidurals are the most effective and consistently reliable way of relieving childbirth pain.
The aim is to provide analgesia by blocking the A-delta and C fibres of the spinal segments
involved in the transmission of labour pain. Neuraxial analgesia must block T10 to L1 for the
first stage of labour and extend to S2 to S4 during the late first stage and second stage of
labour. Low-dose mixtures of local anaesthetics and opioids have improved the quality of
analgesia and reduced adverse effects for both the  mother and neonate. Ambulatory labour
epidurals that preserve motor function have several potential advantages, such as lower
instrumental delivery rates and higher maternal satisfaction.
Labour analgesia should be provided upon request, rather than at a specific degree of
cervical dilation. Previous concerns that early epidural initiation (when cervical dilatation <4
cm) would increase the rate of instrumental delivery and Caesarean delivery have been
dismissed. Epidural analgesia also has no impact on the risk of long-term backache and does
not appear to have an immediate effect on neonatal status as determined by Apgar scores.
Epidural analgesia in itself does not increase the risk of general anaesthesia in the
peripartum period, and in the absence of other risk factors, women with a labour epidural
may eat and drink freely.

Epidural Anaesthesia
 
Traditional epidural labour analgesia was initiated with 0.25% – 0.5% bupivacaine and
maintained with intermittent bolus doses of similar anaesthetic solutions. Current
techniques rely on low dose local anaesthetics combined with an opioid, e.g.; bupivacaine
0.0625 to 0.1% with 2 mcg/ml of fentanyl or ropivacaine 0.08 to 0.2% with 2 mcg/ml of
fentanyl. A 40-50% dose reduction in local anaesthetic requirement can be expected from
the presence of opioids compared with no opioid, at least for first-stage analgesia.
Intermittent boluses (by the anaesthesia provider or by a midwife) can provide satisfactory
analgesia but requires the constant availability of a clinician capable of providing boluses.
Continuous infusions (6 to 12 mls/hr) of low concentrations of local anaesthetic/opioid
result in less variability in the quality of analgesia and require clinician boluses only for
breakthrough pain. Patient-controlled epidural analgesia (PCEA), with or without
background continuous infusion; or by programmed intermittent bolus, with or without a
background infusion (PIEB), has become the preferred technique for maintenance of labour
analgesia; however, this requires specialised electronic infusion pumps .

The conduct of epidural analgesia for labour requires the anaesthesia provider to explain
the procedure and gain consent for the procedure. A skilled assistant must be in attendance
during the insertion and after the block has been established. The assistant should help to
position the patient and perform 5 minutely observations of maternal blood pressure and
heart rate, height of the block and foetal heart rate for 20 minutes after the establishment
of the epidural block or after a top-up. Where an epidural infusion is in use in labour and the
block is stable, observations can be performed half-hourly with continuous CTG monitoring.

Preparation for neuraxial labour analgesia should include the following:

1. Perform a focused history and examination to exclude absolute and relative

contraindications for an epidural.
Absolute contraindications include patient refusal, lack of adequate equipment and
medicines, lack of expertise or supervisory staff, severe coagulopathy,  infection at the site
of puncture, uncorrected hypovolaemia, stenotic cardiac lesions, and unstable neurological
disease.
Relative contraindications include a low platelet count, fever, and raised intracranial
pressure. Patients with a low platelet count may have an epidural provided they do not have
abnormal bleeding. The exact “safe number” of platelets is unknown, but most anaesthesia
providers would offer neuraxial analgesia if the platelet count is greater than 80,000/mm 3.
Fever is not a contraindication to neuraxial block, however, if septicaemia is suspected, this
should be treated with antibiotics before proceeding with neuraxial analgesia. Raised
intracranial pressure from a supratentorial space-occupying lesion is an absolute
contraindication to lumbar puncture because of the risk of coning and compression of the
medulla. As accidental dural puncture may occur during an epidural, in most cases, it is also
prudent to avoid epidural analgesia. Hypovolaemia must be corrected prior to establishing
an epidural.

2. Routine lab work is not required prior to initiation of neuraxial blockade in healthy
parturients. A platelet count may be indicated in selected patients.

3. Consent. 
 Incomplete analgesia (incidence up to 1:5) and the possible need to resite the
epidural. (about 10%)
 Some degree of motor block but shouldn't affect ability to “push”.
 Minor side effects: Drop in blood pressure, nausea, vomiting, shivering, pruritus
 Urinary retention
 Headache due to accidental dural puncture (incidence 1 in 100)
 High/total spinal (1:100,000)
 Nerve injury both temporary (~1:1,000) and permanent (~1:13,000)
  Risk of infection (1:50,000) or haematoma (1:170,000)

4. Intravenous access must be established before the conduct of the epidural. 

5. Resuscitative equipment and medication must be available in the event of hypotension,

high or total spinal anaesthesia, local anaesthetic toxicity or cardiopulmonary arrest. Lipid
emulsion (20 percent) should be immediately available for treatment of local anaesthetic
systemic toxicity.

6. Record a pre-insertion heart rate, blood pressure, temperature and foetal heart rate
(FHR). 

7. Correct patient positioning is probably the most important factor leading to a successful
block. An epidural block can be performed in the lateral or sitting position, and the decision
is usually based on the anaesthesia provider and patient preferences. When the spinous
processes are not easily palpable, the sitting position is preferred. 
After positioning the patient, the skin is prepared with an antiseptic solution. Meticulous
aseptic techniques should be observed. The correct spinal level for epidural insertion is
identified (usually L3/L4 or L4/L5) and local anaesthetic is infiltrated into the skin and
subcutaneous tissues. An 18 or 16 gauge Tuohy needle is inserted with the bevel directed
cephalad. The epidural needle traverses the skin and subcutaneous tissues, supraspinous
ligament, interspinous ligament, the ligamentum flavum and is advanced into the epidural
space. The space has an average depth of about 5 cm (in the range of 3–8 cm in 90% of
individuals) from the skin. A loss of resistance technique with saline or air is used to identify
the epidural space. Compared with air, loss of resistance to saline has the advantage of
providing a more obvious tactile endpoint. Once the epidural space is identified, a 20 gauge
catheter is fed so that 3 to 4 cm remain in the epidural space. After negative aspiration, a
total of 10 to 20 mL of premixed epidural solution (e.g., bupivacaine 0.0625 to 0.1% with 2
mcg/ml fentanyl or ropivacaine 0.08 to 0.2% with 2 mcg/ml fentanyl) is injected in 5 ml
increments, with aspiration between injections, to initiate the block. Every injection (ie, for
initiation of epidural analgesia, top-ups, and dosing for caesarean delivery) should be
treated as a test dose.

Troubleshooting inadequate epidural block:

No effect on labour pain – if after the first dose of low-dose mix there is no effect on pain
and no demonstrable sensory block after 20 minutes, the catheter is unlikely to be correctly
sited in the epidural space. Re-site the epidural if still indicated.

Missed segment – lie the mother affected side down and give a bolus of 10 ml low-dose mix
in 5 ml increments. If no improvement then manage as for a unilateral block.

Unilateral block – withdraw the catheter by 1 – 2 cm and give a further dose of low-dose mix
(e.g. 5 - 10 ml 0.1% bupivacaine + 2 mcg/ml fentanyl) with the mother lying with the
affected side down. If this fails to improve pain relief, consider re-siting the epidural.

Persistent perineal pain – consider sitting and giving a bolus top up of 5-10 mls. 
Persistent pain after bolus – If the mother remains uncomfortable or there is an inadequate
sensory level after a top-up, consider early replacement of the catheter. Once an epidural
needs more than one or two unscheduled boluses, it is more likely to fail for both labour
analgesia and for surgical anaesthesia during caesarean delivery. 

Blood in the Tuohy needle after removal of stylet - reinsert the epidural in a different
interspace. 

Blood through the catheter -  withdraw the catheter 1cm and then flush with saline until no
further blood appears on aspiration, if sufficient catheter remains in space proceed
cautiously with a test dose. If blood is still seen, re-site the epidural at a different interspace.
Low molecular weight heparin should not be given for 12 hours after a bloody tap.

Complications

The complications of epidural analgesia range from the more common but mild to the rare
and catastrophic. 

The autonomic blockade will produce vasodilatation and may create hypotension (10%). If
the block extends to the T1 to T4 fibres, then bradycardia may also occur. Because uterine
blood flow and foetal oxygenation is directly related to maternal arterial pressure,
hypotension must be treated rapidly with lateral uterine displacement, additional
intravenous fluids, and in some occasions, addition of vasopressors.
Shivering is very common. The cause is not clear, but there may be a degree of heat loss
(although the women often do not complain of feeling cold) and it is more common with
larger doses of local anaesthetic. Approximately 30% of parturients will experience an
increase in maternal temperature with neuraxial analgesia. 
The incidence and severity of pruritus is dependent on the opioid dose. Most cases of
opioid-induced pruritus are self-limited. Pruritus may be treated with small doses of
naloxone but this can reverse some of the analgesic effect. Antihistamines have little-to-no
effect on centrally induced pruritus but may increase drowsiness.
Backache occurs in up to 50% of women who have had a baby regardless of whether or not
they have received an epidural. Most of this is related to changes in posture, relaxation of
the pelvic joints and childbirth itself. Bruising and tenderness over the insertion site,
however, is common.
Accidental dural puncture is usually recognized when it occurs by the free flow of CSF
through the needle or catheter. The incidence is roughly 1 in 300 epidural insertions. When
it is recognized, there are usually no serious complications. However, 80% of the women will
develop a post dural puncture headache, some of who will require an epidural blood patch. 
A sensory level of T3 (high block) or above can be associated with significant cardiovascular
and respiratory compromise. Involvement of the cranial nerves signifies intracranial spread
of local anaesthetic which will result in complete loss of consciousness and cardiorespiratory
arrest.

Level Symptoms/signs Action

 T1 - T4 Cardiac sympathetics Hypotension Cease epidural injection
Bradycardia Left lateral tilt
I V fluids
Atropine 0.6 mg
Ephedrine 6 mg boluses
Phenylephrine 50 - 100
mcg boluses
Metaraminol 0.5 mg
boluses
Foetal  monitoring

C6 - C8 Arms and hands Tingling hands Reassure

Accessory muscles of Poor grip strength Continuous clinical
respiration monitoring

C3 - C5 Diaphragm Difficulty breathing Supplemental oxygen

Call for help
Assess airway
Prepare for intubation
(RSI)

Intracranial Slurred speech RSI and ventilation

spread Loss of Maintain anaesthesia
consciousness Circulatory support
Consider emergency
delivery

Local anaesthetic toxicity is another potentially severe complication. If injected

intravenously, the large dose used to establish an epidural block may cause sudden
alteration in mental status, severe agitation or a sudden loss of consciousness with or
without tonic-clonic convulsions. Cardiac toxicity may result in sinus bradycardia,
conduction blocks, asystole and ventricular tachyarrhythmias. The immediate management
of suspected local anaesthetic toxicity is to stop injecting the local anaesthetic, call for help
and follow basic life support of DRABC. Seizures may be terminated with midazolam iv 0.1 -
0.2 mg/kg, propofol IV 1 - 1.5 mg/kg or thiopentone IV 125 - 250 mg in incremental doses of
25 mg. Commence cardiopulmonary resuscitation. Manage arrhythmias, recognising that
the arrhythmias may be very refractory to treatment. Give intravenous 20% lipid emulsion
which will chelate local anaesthetics from the systemic circulation. The initial dose of 20%
intralipid is 1.5 ml/kg over 1 minute plus an infusion of 15 ml/kg/hr. If cardiovascular
stability is not restored after 5 minutes, give a maximum of 2 further boluses and double the
infusion rate to 30 ml/kg/hr. Continue CPR throughout treatment with lipid emulsion.
Recovery from local anaesthetic-induced cardiac arrest may take >1 hour.
Epidural infection leading to abscess or epidural haematoma will cause compression of the
spinal cord leading to paraplegia if the mass is not decompressed. This is rare. Abscess
formation complicates around 0.2 – 3.7 per 100,000 obstetric epidurals. The typical clinical
features of  epidural abscess include back pain and tenderness, fever, radiating root pain,
paraesthesia and paraplegia. Diagnosis requires a high index of suspicion and modern
imaging techniques. Treatment involves early surgical drainage (within 6 hours) to prevent
permanent deficit and high-dose parenteral antibiotics (6 - 12 weeks) selected with
bacteriological advice. 
Neural injury due to parturition (obstetric palsy - often a foot drop or obturator nerve palsy
from a difficult forceps delivery) occurs in one in 3000 deliveries. These are temporary and
resolve within 6 weeks. Similarly, nerve root injuries from an epidural are mostly temporary.
Permanent harm is rare, 0.6 in 100,000. 

In any situation of maternal cardiac arrest with unsuccessful resuscitation, the foetus should
be emergently delivered by caesarean section, if the mother is not resuscitated within 4 min
of the arrest.

Post-dural puncture headache (PDPH)

The incidence of an accidental dural puncture in obstetric epidurals is around 1.5% and 75%
or more of these will develop a post dural puncture headache (PDPH). The pathophysiology
of PDPH remains incompletely understood; however, a dural puncture with a larger needle
is associated with a higher incidence of PDPH, more severe headaches, more associated
symptoms, a longer duration of symptoms, and a greater need for definitive treatment
measures. The cardinal feature of PDPH is its postural nature, with headache symptoms
worsening with sitting or standing, and relieved with lying down. The  headache is often
described as intense, vice-like in the frontal-occipital region,  and always bilateral.
Associated symptoms occur in up to 70 percent of patients, including nausea, neck stiffness,
photophobia and auditory symptoms (hearing loss, tinnitus and hyperacusis). The onset of
symptoms is generally delayed, with the headache usually beginning after 12–48 hours. The
differential diagnosis of headache after dural puncture is broad including migraine,
preeclampsia/eclampsia, subdural haematoma, central venous thrombosis, septic and
aseptic meningitis and pneumocephalus associated with epidural using loss of resistance to
air technique.
Prophylactic measures (bed rest, overhydration, prophylactic epidural blood patch,
medications and intrathecal catheter placement) to prevent the development of a PDPH
after accidental dural puncture are not effective. Whether reinserting the stylet before
removing the spinal needle reduces the risk of PDPH is unclear. Most cases (90%) of PDPH
will resolve spontaneously within 7 - 10 days if left untreated. Mild cases (slight restriction
of daily activities, not bedridden, no associated symptoms) may be treated conservatively
with analgesia. There is no evidence to support bed rest, aggressive hydration, and
intravenous or oral caffeine.
An epidural blood patch (EBP) has been established  as the definitive treatment of PDPH. It
is a procedure in which a small volume of autologous blood is injected into a patient's
epidural space to stop a leak of cerebrospinal fluid. Although EBP can be performed by a
single operator, it usually requires a second operator to obtain the patient’s sterile blood.
Contraindications include anticoagulation/coagulopathy, infection at the injection site,
systemic infection and patient refusal or lack of cooperation. It is usually not offered until
after 24 hours.
The anaesthesia provider should thus locate the space a level below the supposed dural
puncture or if not possible, at the same level as the dural puncture. The site is sterilely
prepped and draped as well as the extremity from which blood is to be drawn. Once the
epidural space is identified, in the standard fashion using a loss-of-resistance technique,
approximately 20 mL of autologous blood is drawn from the patient in a sterile fashion.
Without delay, the blood is slowly injected through the epidural needle until the patient
reports fullness or discomfort in the back, buttocks, or neck. An immediate relief of
symptoms may be experienced by the patient. The patient should be encouraged to lie still
for two hours.
The most frequent complications of EBP include failure (15 to 20%), worsening of PDPH by
accidently creating additional dural punctures, and infection. Mild to moderate back pain is
commonly reported. This is self-limited, generally resolving in days and preferable to the
discomfort of a PDPH. Patients need to be made aware of signs and symptoms of infection
at the injection site: fever, malaise, erythema, or purulence as injected blood may serve as a
nidus for infection.