A 55-year-old man undergoing liver surgery develops metabolic acidosis with pH 7.17, HCO3- 12, Cl- 119, Na+ 145, base deficit -11 after receiving large volumes of fluids. The most likely cause is?

A 55-year-old man undergoing liver surgery develops metabolic acidosis with pH 7.17, HCO3- 12, Cl- 119, Na+ 145, base deficit -11 after receiving large volumes of fluids. The most likely cause is?

• A. Lactic acid
• B. Use of normal saline
• C. Diabetic ketoacidosis
• D. Narcotics

Answer: (B)

Metabolic acidosis with a normal anion gap after large-volume fluid administration points to a chloride-rich fluid–induced acidosis. Normal saline raises serum Cl−; to maintain electroneutrality, bicarbonate declines, lowering HCO3− and pH. Here the anion gap is about Na − (Cl + HCO3) = 145 − (119 + 12) ≈ 14, which is normal, indicating hyperchloremic (non–anion-gap) acidosis rather than lactic acidosis or ketoacidosis. Lactic acidosis would raise the anion gap due to lactate; diabetic ketoacidosis likewise shows a high anion gap with ketones and hyperglycemia; narcotics do not produce this pattern. Thus, the most likely cause is administration of large volumes of normal saline.

Metabolic acidosis with a normal anion gap after large-volume fluid administration points to a chloride-rich fluid–induced acidosis. Normal saline raises serum Cl−; to maintain electroneutrality, bicarbonate declines, lowering HCO3− and pH. Here the anion gap is about Na − (Cl + HCO3) = 145 − (119 + 12) ≈ 14, which is normal, indicating hyperchloremic (non–anion-gap) acidosis rather than lactic acidosis or ketoacidosis. Lactic acidosis would raise the anion gap due to lactate; diabetic ketoacidosis likewise shows a high anion gap with ketones and hyperglycemia; narcotics do not produce this pattern. Thus, the most likely cause is administration of large volumes of normal saline.