Question 12.3

College answer

a) 
Metabolic acidosis 
Concomitant respiratory alkalosis  
Elevated anion gap 
Delta ratio 2.6 – concomitant metabolic alkalosis 
 
Salicylate toxicity

Sepsis with vomiting/pain

Any other plausible. 
 

Discussion

Another disembodied gas, not even a stumpy end of a clinical setting. 

To approach this systematically:

1. We weren't asked about the oxygenation ("describe the acid base abnormalities" they asked) and  so it would attract no marks to point out that there is a substantial A-a gradient (235, a P/F ratio of 180). 
2. There is a normal pH
3. There is a metabolic acidosis with a base deficit of -10. The expected CO₂ is actually 30 (or 29 by the Boston rules); therefore there is also a respiratory alkalosis
4. The anion gap is (145+4.2) - (93+14) = 42.2; or 38 sans potassium. Whichever rules you use, clearly there's an anion gap problem.

And so the SAQ unravels  with a tedious inevitability. What could give rise to a high anion gap without much of an acidosis?  For 20% of a 10-mark SAQ, you are only expected to give one differential ("suggest a possible cause", they asked).  The patient is also a bit hypoxic, so - with some stretch of  the imagination - one could generate a multiple myeloma scenario where there is renal failure with some fluid overload and pulmonary oedema, and  the additional anions are accounted for by a raised phosphate and paraprotein. Any other plausible. A reader has submitted euglycaemic DKA as a completely sensible alternative (Rawla et al, 2017)