An intraoperative ABG reveals metabolic acidosis with elevated lactate. What is the most likely interpretation?

• A. Normal tissue perfusion with adequate oxygen delivery
• B. Hyperchloremic metabolic acidosis from saline
• C. Likely tissue hypoperfusion or sepsis; evaluate for hypoxia, low cardiac output, or major blood loss
• D. Respiratory alkalosis due to hyperventilation

Answer: (C)

Elevated lactate with metabolic acidosis means tissues are not getting enough oxygen and are shifting to anaerobic metabolism. In the operating room, this points to impaired tissue perfusion or a systemic inflammatory/shock state. The most likely scenarios are reduced oxygen delivery due to hypovolemia or major blood loss, decreased cardiac output, or sepsis, all of which can lead to hypoperfusion and lactate accumulation. Lactate is produced when cells rely on anaerobic glycolysis and is normally cleared by the liver and kidneys; when perfusion falters, lactate rises and the acidemia worsens. So, the finding most strongly suggests tissue hypoperfusion or septic physiology, and you should assess and optimize hemodynamics, oxygenation, and perfusion (check perfusion pressure, cardiac output, blood loss, hemoglobin/oxygen content, and signs of infection). The other possibilities don’t fit with lactate elevation: saline-induced hyperchloremic acidosis typically does not raise lactate, and a respiratory alkalosis from hyperventilation lowers CO2 rather than elevating lactate.