In a patient with septic shock and poor tissue perfusion, the most likely contributor to anion gap metabolic acidosis is which of the following?

• A. Hyperkalemia
• B. Metabolic alkalosis
• C. Lactic acid accumulation
• D. Hypercalcemia

Answer: (C)

When tissue perfusion is inadequate, cells switch to anaerobic metabolism and produce excess lactate. Lactate is an unmeasured anion in the blood, so its accumulation raises the anion gap (Na minus the sum of chloride and bicarbonate). This lactate buildup is the classic driver of high anion gap metabolic acidosis in septic shock, reflecting profound tissue hypoxia and impaired clearance in severe illness.

The other options don’t fit this scenario: hyperkalemia is a potassium disturbance, not a primary driver of anion gap increase; metabolic alkalosis involves a rise in bicarbonate and pH, not acidosis; hypercalcemia does not typically cause anion gap metabolic acidosis.