Managing Metabolic Acidosis in Anesthetized Patients

Primary Causes and Diagnostic Approach

The American Society of Anesthesiologists recommends suspecting hyperchloremic metabolic acidosis from excessive normal saline administration, ongoing hemorrhage, tissue hypoperfusion, or inadequate ventilation causing respiratory acidosis in anesthetized patients with decreasing base excess despite fluid resuscitation 1, 2
Administration of 0.9% normal saline or unbalanced colloid solutions is the leading cause of worsening base excess during anesthesia, due to supraphysiologic chloride concentrations 1, 2
The European Society of Anaesthesiology recommends checking for surgical bleeding, reassessing hemodynamic parameters, and considering invasive monitoring to guide resuscitation in cases of suspected ongoing hemorrhage or inadequate resuscitation 3, 4
Tissue hypoperfusion from inadequate cardiac output generates lactic acidosis, progressively decreasing base excess, and the American Heart Association recommends maintaining mean arterial pressure with vasopressors once normovolemia is established 1, 5

The American College of Surgeons recommends obtaining arterial blood gas immediately to calculate anion gap and differentiate high anion gap acidosis from hyperchloremic acidosis, and checking serum chloride, sodium, and lactate levels 2
The Society of Critical Care Medicine recommends assessing adequacy of resuscitation by evaluating hemodynamic parameters, considering cardiac output monitoring, and measuring core temperature 3, 4, 5
The American Society of Anesthesiologists recommends stopping all chloride-rich fluids and switching to balanced crystalloids, maintaining mean arterial pressure with vasopressors, and targeting near-zero fluid balance to avoid complications from fluid overload 1, 2, 5, 6

The American Society of Anesthesiologists recommends avoiding continued normal saline administration, as it worsens hyperchloremic acidosis and is associated with increased 30-day mortality, acute kidney injury, and increased vasopressor requirements 1, 2
The European Society of Anaesthesiology recommends avoiding assumption of fluid responsiveness without assessment, as epidural anesthesia causes functional hypovolemia through vasodilation, not actual volume loss 3, 4
The American College of Surgeons recommends avoiding overlooking occult hemorrhage, as elderly patients and those on beta-blockers may not mount tachycardic response to bleeding 3, 4