In septic shock, the predominant reason for metabolic acidosis is lactic acid accumulation from tissue hypoperfusion. Which option best describes this mechanism?

• A. Metabolic acidosis due to lactic acid accumulation from tissue hypoperfusion
• B. Metabolic alkalosis due to loss of bicarbonate from diarrhea
• C. Respiratory acidosis due to CO2 retention
• D. Mixed metabolic and respiratory acidosis with compensatory mechanisms

Answer: (A)

In septic shock, poor tissue perfusion means cells receive less oxygen, so they switch to anaerobic metabolism and produce lactic acid. This excess lactic acid donates hydrogen ions, lowering pH, while bicarbonate is used up buffering those ions. The result is a metabolic acidosis driven by elevated lactate from tissue hypoperfusion, often presenting as a high anion-gap metabolic acidosis. While you can see other acid–base disturbances in critically ill patients, the dominant mechanism here is lactic acid buildup due to impaired tissue oxygenation.