A 30 year old man is brought to your ED by ambulance. He was found lying on his garage floor unconscious by his girlfriend after an earlier argument. He is a NIDDM on Metformin and has some psychological problems on Quetiapine.

Answer

pH 7.05 and HCO3 10mmol/l – metabolic acidosis

Compensation – expected PCO2 = HCO3 x 1.5 + 8 = 23

AG = Na – (Cl+HCO3) = 29

Delta ratio = Change in AG/change in HCO3 = 1.2

Osmolar gap =  measured osmolality – calculated osmolality

Convert all unis to mmol/l – Ethanol mmol/l = %ethanol x 218 = 17.44 mmol/l

Calculated osmolality = (2x Na)+urea+glucose+ethanol = 319.4

Therefore Osmolar Gap = 10.6

Severely raised lactate of 18, mild hypocalcaemia and mildly elevated creatinine

The above VBG shows a compensated HAGMA, with a markedly raised lactate and mild hypocalcaemia and mildly elevated creatinine and osmolar gap. The patient is normoglycaemic.  In this clinical context toxins are the most likely cause.  A HAGMA with a markedly elevated lactate hypocalcaemia and renal impairment is suggestive of ethylene glycol overdose, which this patient would have easy access to through substances used in his garage like brake fluid, antifreeze.  Other toxins to consider would be a metformin overdose which would give a normoglycaemia, and a severe lactic acidosis. A polypharmacy OD is likely as the patient has access to antipsychotic medication.

A raised osmolar gap suggests the presence of unmeasured (potentially toxic) osmotically active compounds. If one suspects toxic alcohol ingestion high osmolarity and osmolar gap helps with the diagnosis and can be used when serum methanol and ethylene glycol levels are not readily available.  But a normal osmolality and osmolar gap does not exclude a potentially life threatening toxic alcohol ingestion, as late in the clinical course the parent compounds are metabolised to non osmotically active compound

Non tox causes of raised osmolar gap – CRF, hyperlipidaemia, hyperproteinaemia, ketoacidosis, severe lactic acidosis, massive hyperMg.