PRACTICE

RATIONAL TESTING
Interpreting arterial blood gas results
Nicholas J Cowley,1 Andrew Owen,1 Julian F Bion2
1
Department of Anaesthesia and You have been called to see a 69 year old man on a surgical Table 1 | Report of arterial blood gases for the hypothetical patient
Critical Care, Queen Elizabeth ward because he has become drowsy and short of breath. described
Hospital Birmingham, Birmingham He had a large bowel resection the previous day, has a back- Value (reference range)
B15 2WB, UK
2 ground of type 2 diabetes, and is a current smoker. On exami- pH 7.25 (7.35-7.45)
University Department of
Anaesthesia and Intensive Care nation his arterial blood pressure is 104/65 mm Hg, his heart Partial pressure of oxygen (PaO2) (kPa) 8.9 (11-13)
Medicine, Queen Elizabeth rate 132 beats/min and irregular, and his respiratory rate 22 Partial pressure of carbon dioxide (PaCO2) (kPa) 5.9 (4.7-6.0)
Hospital, Birmingham B15 2TH breaths/min; his oxygen saturations with pulse oximetry are Standard bicarbonate (sHCO3−) (mmol/L) 18.5 (22-26)
Correspondence to: N J Cowley Base excess (mmol/L) −7.0 (−2 to +2)
n.j.cowley@bham.ac.uk 94% on supplemental oxygen via a 40% Venturi-type mask.
He is slightly confused and is complaining of abdominal pain Haemoglobin g/dL 6.1 (13-17)*
Cite this as: BMJ 2013;346:f16
Sodium (Na+) (mmol/L) 148 (136-145)
doi: 10.1136/bmj.f16 despite using patient controlled an­algesia with morphine. His
Potassium (K+) (mmol/L) 3.0 (3.5-5.0)
chest is clear on auscultation.
This series of occasional articles Calcium (Ca++) (mmol/L) 1.2 (1.1-1.4)
provides an update on the best Chloride (Cl−) (mmol/L) 108 (98-106)
use of key diagnostic tests in the What is the next investigation? *61 (130-170 g/L).
initial investigation of common or You take a blood specimen for analysis of arterial blood gases
important clinical presentations.
The series advisers are Steve Atkin, for rapid biochemical evaluation to guide diagnosis and ini- facemask are rarely accurate. The FiO2 will vary according to
professor, head of department of tial management. Table 1 shows the results. It is important to the oxygen delivery device used, the presence of a reservoir,
academic endocrinology, diabetes, adopt a systematic approach to interpreting results of arterial and the patient’s inspiratory flow rate. A healthy individual
and metabolism, Hull York Medical
School; and Eric Kilpatrick, blood gases, as outlined in table 2, preceded by a brief history would be expected to have a P/F ratio above 50, with lower
honorary professor, department and focused clinical examination. values signifying impaired gas exchange. Patients with acute
of clinical biochemistry, Hull Royal lung injury or acute respiratory distress syndrome have values
Infirmary, Hull York Medical School.
To suggest a topic for this series, Step 1: Assess oxygenation below 40 and 26.7 respectively, in addition to other required
please email us at practice@bmj. Arterial oxygen tension (PaO2) is the partial pressure of oxy- diagnostic criteria.1
com. gen in arterial blood. The main determinants of PaO2 are the The PaO2 in our example patient (8.9 kPa) is below normal,
inspired oxygen concentration, alveolar gas exchange, and, to but as he is breathing supplemental oxygen rather than room
a lesser extent, tissue oxygen consumption. The ratio between air, this represents significant impairment of oxygen uptake,
the PaO2 and the inspired oxygen concentration expressed as probably from intrapulmonary shunting. Intrapulmonary
a fraction (FiO2) is termed the PaO2/FiO2 ratio or the P/F ratio. shunting occurs when areas of lung are perfused without
This is a useful index for determining the presence and severity adequate ventilation—for example, after atelectasis, consoli-
of impaired alveolar gas exchange and is easier to calculate dation, fluid accumulation, or acute inflammation of lung
than alternative indices, such as the alveolar-arterial gradient. tissue. In the calculation of his P/F ratio, the inspired oxygen
Estimations of FiO2 based on oxygen flow through a standard concentration is determined by the Venturi-type mask (in this
case 0.4). Thus, his P/F ratio is calculated as (8.9/0.4 = 22.3),
LEARNING POINTS representing marked impairment in gas exchange.
Be aware that the measurement of oxygen saturation using
Interpretation of arterial blood gases requires a systematic assessment of oxygenation, pH,
standard bicarbonate (sHCO3−) and base excess, partial pressure of carbon dioxide (PaCO2), standard pulse oximetry and some arterial blood gas analysers
and additional analytes may give misleading results. Oxygen saturations are falsely
The P/F ratio (ratio between the PaO2 and the inspired oxygen concentration expressed as a raised in carbon monoxide poisoning (which produces car-
fraction) is a useful guide to the presence and severity of impaired alveolar gas exchange boxyhaemoglobin) and depressed in methaemoglobinaemia,
Reassess all acutely ill patients regularly, and consider repeat arterial blood gas analysis which is caused by various drugs or toxins, including nitrate
Errors in blood gas analysis are dependent more on the clinician than on the analyser fertilisers, some local anaesthetics, and sulphonamide antibi-
otics. These conditions cannot be readily distinguished clini-
cally, and analysers using co-oximetry to analyse haemoglobin
Table 2 | Guide to systematic approach to analysis of a report of arterial blood gases oxygen saturations will report levels of carboxyhaemoglobin
Step 1 Assess Record the inspired oxygen concentration. Calculate the P/F ratio,* particularly if patient and methaemoglobin.2 However, if oxygen saturation is not
oxygenation is receiving supplemental oxygen. Assess haemoglobin saturations, if testing is available available on the analyser, pay close attention to the patient’s
Step 2 Assess pH Is the patient acidaemic or alkalaemic? clinical history.
Step 3 Assess sHCO3− An abnormal base excess and sHCO3− indicates a primary or compensatory
and base excess metabolic acid-base disturbance
Step 4 Assess PaCO2 Is there a primary respiratory acidosis or alkalosis? Is low or high PaCO2
Step 2: Assess pH
compensating for a metabolic acidosis or alkalosis respectively? The respiratory The pH is usually maintained within a tight range between
system will not normally overcorrect a metabolic acid-base disturbance, and so if this 7.35 and 7.45, and a small change in the pH will result in a
is the case, consider a mixed metabolic and respiratory disorder
large change in the hydrogen ion concentration, making even
Step 5 Review Review electrolytes, and consider calculation of anion gap to further assess any
additional metabolic acidosis. Haemoglobin, glucose, and lactate concentrations may be modest derangements in the pH of clinical significance. Our
analytes available and may be helpful in determining the cause of any acid-base abnormality example patient has an acidosis (pH of 7.25) or, more accu-
Step 6 Reassess After institution of a management plan, repeat clinical assessment and consider rately, an acidaemia (abnormally low blood pH). In some
repeat analysis of arterial blood gases to guide further treatment cases an underlying acid-base disorder can be disguised by

36 BMJ | 16 FEBRUARY 2013 | VOLUME 346

 PRACTICE

Acidaemia pH<7.35
Interpretation of arterial
BE or sHCO3- Negative BE or low sHCO3- Normal BE or sHCO3- Positive BE or high sHCO3-
blood gases in the presence
of acidaemia or alkalaemia, ↓ ↓ ↓
PaCO2 High (>6 kPa) Normal Low (<4.7 kPa) High (>6 kPa) High (>6 kPa)
with examples of common
diagnoses ↓ ↓ ↓ ↓ ↓
Diagnosis Mixed respiratory and Metabolic Metabolic acidosis; Respiratory acidosis Respiratory acidosis;
metabolic acidosis acidosis respiratory compensation renal compensation
Examples Lactic acidosis Opiate excess Long term respiratory
Diabetic ketoacidosis Severe acute ventilatory disease (eg chronic
Chronic renal failure failure obstructive pulmonary
Self poisoning (many drugs) Airway obstruction disease, thoracic
Chloride excess (eg iatrogenic saline infusion) abnormalities)

Alkalaemia pH>7.45
BE or sHCO3- Positive BE or high sHCO3- Normal BE or sHCO3- Negative BE or low sHCO3-
↓ ↓ ↓
PaCO2 High (>6 kPa) Normal Low (<4.7 kPa) Low (<4.7 kPa) Low (<4.7 kPa)
↓ ↓ ↓ ↓ ↓
Diagnosis Metabolic alkalosis; Metabolic Mixed respiratory and Respiratory alkalosis Respiratory alkalosis;
respiratory compensation alkalosis metabolic alkalosis renal compensation
Examples GI loss (eg vomiting, loss of colonic secretions) Anxiety Pregnancy
Electrolyte disturbance (eg hypokalaemia, Central causes (eg brain Central causes
hypomagnesaemia, hypercalcaemia) injury)
Drug ingestion (eg calcium carbonate, thiazide, loop diuretics) Drugs (eg salicylates, caffeine)
Endocrine (eg hyperaldosteronism)
BE = base excess
sHCO3- = standard bicarbonate concentration
PaCO2 = partial pressure of carbon dioxide

compensatory mechanisms that normalise pH, referred to as usually caused by inadequate organ perfusion. Trends in
a compensated acidosis or alkalosis. lactate concentrations are useful in guiding response to treat-
ment.4  5 A metabolic acidosis with a normal anion gap is
Step 3: Assess standard bicarbonate (sHCO3−) and base usually accompanied by hyperchloraemia, causes of which
excess include iatrogenic saline infusion as well as gastrointestinal
Most blood gas analysers will calculate values for standard loss of bicarbonate from diarrhoea or renal loss of bi­carbonate
bicarbonate (sHCO3−) and base excess, either of which can (such as renal tubular acidosis type I and II).
be used to isolate metabolic causes of acid-base disturbance.
These values are particularly useful when the cause of the acid- Step 4: Assess arterial partial pressure of carbon dioxide
base disorder has both metabolic and respiratory components. (PaCO2)
The contribution of any respiratory acid-base disorder to the The arterial partial pressure of carbon dioxide (PaCO2) should
sHCO3− concentration and base excess is removed by the be assessed next to identify any ventilatory component in the
analyser’s software, which adjusts the carbon dioxide to the acid-base disturbance. A raised PaCO2 value will contribute
normal value of 5.3 kPa. In the case of metabolic acidosis, we towards an acidosis, and a low value towards an alkalosis. In
bmj.com would expect to see a reduction in the sHCO3− concentration, our patient the PaCO2 value is not raised, indicating that the
Previous articles in this and a more strongly negative base excess (commonly termed acidosis is not respiratory in origin. If respiratory drive were
series a base deficit). For the patient in our example, the acidosis is normal, compensatory hypocarbia would be expected. How-
ЖЖInvestigating an likely to be metabolic in origin, given the depressed sHCO3− ever, in our example, the patient’s PaCO2 (5.9 kPa) is at the
incidental finding of concentration of 18.5 mmol/L, and negative base excess of upper limit of normal, indicating an inadequate ventilatory
thrombocytopenia −7.0 mmol/L. Normal values for standard bicarbonate sHCO3− response, which could be caused by opioid analgesia, coexist-
(BMJ 2013;346:f11) and base excess exclude metabolic acid-base disturbance, ent chronic obstructive pulmonary disease, severe abdominal
ЖЖMonitoring and a raised sHCO3− concentration and positive base excess pain splinting breathing, or incipient ventilatory failure. Thus
aminoglycoside level in­dicate a metabolic alkalosis. The figure shows the common our patient has a metabolic acidosis without respiratory com-
acid-base disturbances. pensation.
(BMJ 2012;345:e6354)
A metabolic acidosis can be characterised further by deter- The presence of a normal PaO2 value, or normal values on
ЖЖInvestigating an
mining the anion gap from the information on the blood gas pulse oximetry, does not rule out respiratory failure, particu-
incidental finding of a
report. The anion gap is the difference between the anions larly in the presence of supplemental oxygen. An unexpectedly
paraprotein and cations that are measured as standard (Na+, K+, Cl−, and high PaCO2 value is a more sensitive marker of ventilatory fail-
(BMJ 2012;344:e3033) HCO3−), calculated with the formula: ((Na+) + (K+)) − ((Cl−) + ure than pulse oximetry or PaO2, particularly in the presence of
ЖЖInvestigating asthma (HCO3−)). A rise from a normal value of 10 (reference range supplemental oxygen, as it has a close relationship with depth
symptoms in primary care 6-14) mmol/L indicates an excess of unmeasured anions, and rate of breathing.
(BMJ 2012;344:e2734) which are responsible for the underlying acidosis, causes of
ЖЖInterpreting and which include lactic acidosis, ketoacidosis, renal failure, and Step 5: Assess additional analytes
investigating proteinuria toxins.3 Many blood gas analysers are able to detect lactate, Many “point of care” arterial blood gas analysers can now
(BMJ 2012;344:e2339) one of the commonest causes of raised anion gap acidosis, evaluate electrolytes, haemoglobin, glucose, and lactate. The

BMJ | 16 FEBRUARY 2013 | VOLUME 346 37

 PRACTICE

Table 3 | Sources of error in analysis of arterial blood gases Step 6: Reassess

Type of error Consequence
After the start of treatment, regular reassessment will be
Errors before and after analysis needed. Repeated blood gas analysis can demonstrate
Patient identification error Wrong patient treated response to treatment and guide further treatment. In a
Contamination of sample—eg dilution Inaccurate values high dependency setting, consider inserting an arterial can-
by flush from indwelling arterial cannula nula for obtaining repeated specimens to avoid multiple
Incorrect sampling tubes—eg excess Sample dilution and measurement errors arterial punctures.
heparin anticoagulant
Haemolysis of blood Errors in measurement of electrolytes and packed cell volume
Accuracy
Air bubbles in specimen Falsely raises PaO2 and pH and lowers PaCO2
With advances in machine performance and quality assur-
Sample not representative If supplemental oxygen is added or removed around time of analysis, results
may be unrepresentative. Ensure supplemental oxygen is recorded on ance,6‑8 two thirds of errors in point of care analysis of arterial
report blood gases are now attributable to clinicians.9  10 Attention to
Delay in processing the sample Ongoing metabolism within sample falsely raises PaCO2 and lowers PaO2 detail in sampling technique and processing is thus essential
and pH
(table 3). If obtaining an arterial sample is difficult, venous
Analytical errors
blood (taken without a tourniquet) will provide a reason-
Calibration error Drift may cause inaccuracy—many machines suppress results if unreliability
is detected able substitute for all analytes other than PaO2, although this
Interference Examples: haemolysis, icterus, and lipaemia can cause inaccuracies should be clearly marked as such to avoid confusion in inter-
Measurement method Example: haemoglobin measured using “conductivity” may be inaccurate pretation.
in certain situations
Hypothermia Results will differ if analysis is corrected to the patient’s body temperature, Outcome
although the merits of performing this correction are debated. If this
information is inputted, analysers may present results corrected for body
Our patient received adequate analgesia to allow more com-
temperature, as well as uncorrected fortable breathing and was monitored closely for evidence of
bleeding. He received fluid therapy and a blood transfusion,
additional information, available within minutes of the pri- which coincidentally increased the serum potassium con-
mary assessment, can aid diagnosis and guide early treatment. centration. This treatment caused resolution of his acid-base
The patient in our example has hypokalaemia (potassium disturbance on subsequent arterial blood gas analysis, as well
3.0 mmol/L). This has probably precipitated atrial fibrilla- as spontaneous reversion to sinus rhythm.
tion, which will impair his cardiac output. His haemoglobin Contributors: All authors have participated in the planning, drafting, and
concentration of 6.0 g/dL (60 g/L) is low; occult haemorrhage revising of this manuscript. JFB is the guarantor.
Competing interests: None declared.
with inadequate tissue oxygen delivery might have caused the
Provenance and peer review: Commissioned; externally peer reviewed.
metabolic acidosis. This is a particular risk in the postoperative Patient consent not required (patient anonymised, dead, or hypothetical).
setting when oxygen demand is increased. References are in the version on bmj.com.

10-MINUTE CONSULTATION
Dry eye
Louis Tong,1 2 Jeremy Tan,3 4 Julian Thumboo,4 5 Gabriel Seow6
Cite this as: BMJ 2012;345:e7533 A 30 year old woman visits her general practitioner complain- Is the dry eye part of a systemic condition?—Take note of a
doi: 10.1136/bmj.e7533 ing of itchy eyes for six months, aggravated by computer use dry mouth (suggesting Sjögren’s syndrome), and review for
This is part of a series of occasional in her job as a clerk. Dry eye is a common multifactorial condi- common systemic illnesses and drugs that worsen dry eye
articles on common problems in tion of the tear and ocular surface. In ambulatory settings it (box). Ask about history of orbital radiation and any ocular
primary care. The BMJ welcomes may commonly result from increased tear evaporation (result- (especially refractive), facial, and intracranial surgery.
contributions from GPs.
ing from, for example, blepharitis or contact lens wear); tear Are there any red flags?—Warning signs of more serious
1
Department of Cornea and External hyposecretion (from, for example, age related or anticholiner- conditions include an acute history, persistent or profound
Eye Disease, Singapore National Eye
Centre, Singapore
gic drugs); and mucous dysfunction (mucus secreting goblet visual loss, associated diplopia, and systemic ill health
2
Office of Clinical Sciences, Duke-NUS cells in the conjunctiva may be damaged after previous infec- evidenced by loss of weight or fever.
Graduate Medical School, Singapore tious conjunctivitis). Severe dry eye resulting from systemic
Examination
3
Faith Medical Group, 211 Toa Payoh diseases is uncommon in primary care but conditions predis-
Lorong 8, #01-19, Singapore
4
posing to dry eye should be documented (box). Mild conjunctival redness or a grossly normal eye could indi-
Department of Medicine, Yong Loo
Lin School of Medicine, National cate dry eye. Dry eye may be confused with allergic and infec-
University of Singapore, Singapore What you should cover tive conjunctivitis. A series of steps can help doctors to make
History
5
Department of Rheumatology and a probable diagnosis:
Immunology, Singapore General
Hospital, Singapore
Are the symptoms consistent with dry eye?—Ask about •   Inspect and evert lids. Large subtarsal papillae suggest
6
Woodlands Clinic, Blk 131, symptoms of dry eye, such as chronic burning, grittiness, allergic conjunctivitis, especially in a patient with a
Marsiling Rise #01-204, Singapore and visual fluctuations. Paradoxically, patients may history of atopy, asthma, eczema, or contact lens use.
Correspondence to: L Tong, complain of watery eyes owing to eye irritation and Subtarsal petechiae or membranes suggest infective
Singapore National Eye Centre,
11 Third Hospital Avenue,
reflex tearing. A complaint strongly suggestive of dry eye conjunctivitis
Singapore 168751 is worsening of symptoms by prolonged visual tasks, •   Conjunctiva. Look for copious discharge or chemosis
Louis.tong.h.t@snec.com.sg exposure to wind, and air conditioning. suggesting infective conjunctivitis, and sectorial redness

38 BMJ | 16 FEBRUARY 2013 | VOLUME 346

 PRACTICE

suggesting episcleritis
Systemic causes of dry eye USEFUL RESOURCES
•   Proptosis and lid lag suggest thyroid eye disease Dry Eye Company (www.dryeyezone.com)—US resource for
Endocrine
•   Red reflex. Irregular pupil suggest uveitis treatment and relief of severe or chronic dry eye conditions
Post-menopausal state* or
•   Visual acuity should not be severely impaired in dry Clinical Knowledge Summaries (www.cks.nhs.uk/dry_eye_
post-oophorectomy
eye, as blinking helps to maintain normal acuity during syndrome)—Diagnosis and management information about dry eye
Diabetes mellitus*
examination. Prodigy (http://prodigy.clarity.co.uk/dry_eye_syndrome)—
Thyroid disease*
The examination should focus on: the skin (acne, eczema, Diagnosis and management information about dry eye
Dermatological malar rash, target lesions); finger joints (features of rheuma- 2007 Report of the International Dry Eye WorkShop (DEWS). Ocular
Rosacea* toid arthritis); neck (goitre); Parkinsonian fe­atures (in Parkin- Surface 2007(5). www.tearfilm.org/dewsreport/pdfs/TOS-0502-
Stevens-Johnson syndrome son’s disease there is reduced blinking, resulting in excessive DEWS-noAds.pdf
Mucous membrane tear evaporation between blinks).
pemphigoid
Schirmer’s testing, fluorescein dye, and slit lamp micro- need to continue wearing contact lenses; (b) drugs with
Neurological scopes are needed for a formal diagnosis of dry eye, and com- antimuscarinic side effects—for patients taking tricyclic
Parkinson’s disease* munity optometrists have access to these. antidepressants, consider alternatives such as selective
Drug induced serotonin reuptake inhibitors (also, the use of oral
Tricyclic antidepressants What you should do antihistamines should not be prolonged unnecessarily).
(anticholinergic effect)* •   Reassure the patient if no red flags are present. Dry eye is a •   Manage commonly associated conditions. Ocular
Antihistamines chronic condition but does not threaten sight. irritation will improve if allergic conjunctivitis,
(anticholinergic effect)*
•   Start artificial tears (lubricant eye drops), the mainstay of blepharitis, and rosacea are treated.
Lacrimal gland related management. Reassure the patients that preservative-free •   Refer to an ophthalmologist (a) urgently, if the red flags
Lymphoma and leukaemia formulations can be used as often as desired and titrated mentioned above are detected; and (b) routinely, if
Orbital radiation to visual activities. If initial formulations do not relieve symptoms persist (may need punctal plugs, ciclosporin,
Surgery symptoms, consider adding transient gels, or hypo- and steroids).
Autoimmune osmolar eye drops that contain hyaluronate and lipids. Competing interests: LT was supported for the submitted work by the Singapore
Primary Sjögren’s syndrome Ointments and viscous gels are best used before bedtime National Research Foundation under its clinician scientist award NMRC/
CSA/013/2009 and administered by the Singapore Ministry of Health’s National
Secondary Sjögren’s as these induce blurring. Some trial and error may be Medical Research Council, and by the Singapore Ministry of Health’s National
syndrome (that is, necessary to determine what is most comfortable for each Medical Research Council under its individual research grant NMRC/1206/2009
associated with systemic patient. and centre grant NMRC/CG/SERI/2010. All authors have no financial
lupus erythematosus, relationships with any organisations that might have an interest in the submitted
•   Consider aggravating factors, such as (a) contact lenses— work in the previous three years; and no other relationships or activities that
rheumatoid arthritis, or other
these should be removed for the day when dry eye could appear to have influenced the submitted work.
autoimmune diseases)
*The most common systemic causes
symptoms appear, and patients could consider the newer Provenance and peer review: Not commissioned; externally peer reviewed.
of dry eye found in general practice silicon-hydrogel or rigid gas permeable lenses if they Accepted: 31 October 2012

ANSWERS TO ENDGAMES, p 40 For long answers go to the Education channel on bmj.com

STATISTICAL QUESTION PICTURE QUIZ A rash in a patient with neutropenia
Stratified random allocation 1 There are two annular macular erythematous lesions overlying the left knee. The largest is about 3
Statements a, c, and d are true, whereas b cm in diameter and has a dusky necrotic centre. The smaller 1 cm lesion also has a darker centre.
is false. 2 A persistent fever in a neutropenic patient, which does not respond to broad spectrum antibiotics,
raises the possibility of an invasive fungal infection. The development of multiple randomly
ANATOMY QUIZ distributed and centrally necrotic skin lesions with lung consolidation is classic for disseminated
Oblique radiograph of the Fusarium infection. Fusarium spp are ubiquitous environmental moulds that are an increasingly
common cause of opportunistic infection in immunocompromised patients.
normal lumbar spine
This is the pars interarticularis (part 3 The differential diagnosis for multiple macular centrally necrotic skin lesions includes bacterial soft
between the two articular processes) of tissue infection (such as ecthyma or ecthyma gangrenosum), other invasive fungal infections (such
the vertebra, also known as the “Scottish as Aspergillus or Candida), and cutaneous vasculitis.
terrier dog sign.” 4 Perform a comprehensive screen for bacterial and fungal infection. This should include skin swabs
A: Superior articular process (forms the ear) from an ulcerated lesion, blood cultures, and skin biopsy (for histology and tissue culture). An
B: Pedicle (forms the eye) echocardiogram should be performed to exclude infective endocarditis. With evidence of lower
C: Transverse process (forms the nose) respiratory tract consolidation, bronchoalveolar lavage could be considered.
D: Pars interarticularis (forms the neck).
5 International and national guidelines exist for the management of invasive fungal infections
The sign of a “neck break” is indicative of
in patients with haematological cancer. First line empirical antifungal agents primarily target
spondylolysis
Aspergillus and Candida. Fusarium is typically resistant to echinocandins (such as caspofungin),
E: Lamina (forms the body)
so if this organism is considered in the differential diagnosis, liposomal amphotericin B would be a
F: Inferior articular process (forms the
suitable first line agent. Specialist local microbiologist advice should be sought.
foreleg)

BMJ | 16 FEBRUARY 2013 | VOLUME 346 39