NBME 21 Answers ↦
why did the stem say she had a drinking problem... is that just a distractor?
I think alcohol uses up all the NAD+ in its metabolism leading to increased NADH/NAD ratio. After that, TCA cannot progress and the cell is forced to use anaerobic metabolism, which increases lactate. lactate causes anion gap metabolic acidosis (L in MUDPILES from first aid)
She may also have ingested methanol if she couldn't get her hands on regular ethanol which causes an anion gap metabolic acidosis (M in mudpiles).
winter's formula is to look at the compensation to see if it is appropriate.
PCO2 = 1.5[HCO3-] + 8 +/- 2
In this case, 1.5* 10 (Pt's bicarb) +8 +/-2 = 21 to 25
Pt's PO2 is 23, so compensation is appropriate. If PCO2 was below 21, it would be concomitant respiratory alkalosis
in other words, winter's formula is not necessary for this question
@ergogenic22 Someone might use Winter's formula to rule out choice A.
Isn't the low pCO2 enough to rule out A?