Which scenario is most likely to cause lactic acidosis contributing to anion gap metabolic acidosis?

• A. Severe diarrhea causing bicarbonate loss
• B. Hypoventilation leading to respiratory acidosis
• C. Lactic acidosis from tissue hypoperfusion (shock)
• D. Hypovolemia without acidosis

Answer: (C)

Lactic acidosis raises the anion gap because lactate is an unmeasured anion that accumulates when there isn’t enough oxygen for normal cell respiration. In tissue hypoperfusion, cells rely on anaerobic glycolysis, producing excess lactate. This lactate is buffered by bicarbonate, lowering bicarbonate levels and increasing the measured anion gap, a hallmark of high anion gap metabolic acidosis.

Severe diarrhea drains bicarbonate from the gut, causing a metabolic acidosis with a normal (hyperchloremic) anion gap, not lactate-driven. Hypoventilation produces respiratory acidosis, not a metabolic acidosis with lactate. Hypovolemia without acidosis implies adequate tissue oxygenation or no lactate buildup, so it doesn’t account for lactic acidosis contributing to the anion gap. The scenario described—tissue hypoperfusion (shock) leading to anaerobic metabolism and excess lactate—best explains lactic acidosis contributing to anion gap metabolic acidosis.