Lab Case 56 – Interpretation

Critically unwell patient with low GCS 

1. High anion gap metabolic acidosis

normal delta gap

additional respiratory acidosis

very high A-a gradient

Elevated lactate, glucose

Consider CO poisoning, other causes of high lactate, toxins

check renal function and ketones (DKA unlikely)

2. Tests

Bedside –

CO and MetHb levels –

CO level


Room air 2-3 hours

100% O2 30-90 minutes

100% O2 at 2-3 atm 23 minutes


Lab –

renal function




Coags and D dimer





(In women pregnancy test)

Radiology –


CT head/ MRI

3.  “If you’re cherry red, you’re dead”

Severe life threatening CO poisoning requiring urgent discussion with hyperbaric

ABC approach to treatment – intubate and hyperventilate with 100% oxygen

CO levels and symptoms -Symptoms may not correlate well with HbCO levels.

Symptoms may not correlate well with HbCO levels.

<10%  Background level in smoker
10%     mild H
20%     dizziness, N, dyspnoea, throbbing headache
30%     Vertigo, ataxia, visual disturbance
40%     confusion, coma, seizures, syncope
50%     CVS, Respiratory failure, arrhythmia, seizures, death

High Risk Features for Neuropsychiatric sequelae:

significant LOC or coma
Persistent neurological disturbance such as confusion
Abnormal Cerebellar examination
Metabolic acidosis
Myocardial ischaemia
Age over 55

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