NBME 21 Primary metabolic acidosis with increased anion gap (NBME Answers)

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Retired NBME 21 Answers

nbme21/Block 1/Question#10 (reveal difficulty score)
A 34-year-old woman is brought to the ...
Primary metabolic acidosis with increased anion gap 🔍 / 📺 / 🌳 / 📖
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submitted by ∗ergogenic22(401)

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Na-(Cl-+HCO3-)=anion gap = 140-(105+10) = 25 mEq/L

normal range for anion gap is 8 to 16 mEq/L...Therefore, positive anion gap.

pH = 7.25, normal range 7.35-7.45... Therefore acidosis

Normal bicarbonate 22-28, questions shows bicarb of 10. Therefore metabolic acidosis

Additionally PCO2 normally 33-45 mm Hg, question shows PCO2 of 23 with normal PO2, therefore respiratory compensation

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mambaforstep why did the stem say she had a drinking problem... is that just a distractor? +1

castlblack 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) +3

nafilnaf 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). +2

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submitted by ∗temmy(153)

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please help according to winters equation the patient has a normal anion gap

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ergogenic22 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 +6

ergogenic22 in other words, winter's formula is not necessary for this question +3

the_sacramento_kings lol unless you want to make sure its not A. +2

hello @ergogenic22 Someone might use Winter's formula to rule out choice A. +1

maxillarythirdmolar respiratory depression of alcohol should rule out "A" +1

baja_blast Isn't the low pCO2 enough to rule out A? +2

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