Non-Anion Gap Metabolic Acidosis Association
The correct answer is (b) large amount of saline resuscitation, which causes hyperchloremic metabolic acidosis through excessive chloride administration.
Mechanism of Saline-Induced Non-Anion Gap Acidosis
Hyperchloremic metabolic acidosis has been directly associated with 0.9% NaCl when used as a resuscitation fluid 1. The mechanism involves:
- Excessive chloride administration displaces bicarbonate, maintaining electroneutrality while lowering serum bicarbonate concentration and creating acidosis without increasing unmeasured anions 2
- The resultant acidic milieu can cause cellular dysfunction and contribute to poor clinical outcomes 2
- The change in chloride concentration in the distal tubule lumen may also reduce glomerular filtration rate 2
Why Other Options Are Incorrect
Diabetic ketoacidosis (option c) produces a HIGH anion gap metabolic acidosis, not a non-anion gap acidosis 3. DKA generates ketoacids (unmeasured anions) that increase the anion gap 3. However, during the recovery phase of DKA, patients may develop a transient non-anion gap acidosis as chloride from IV fluids accumulates while ketoanions are metabolized 4.
Cardiogenic shock (option d) and hemorrhagic shock (option e) typically produce lactic acidosis, which is a HIGH anion gap metabolic acidosis due to accumulation of lactate (an unmeasured anion) 1. These shock states cause tissue hypoperfusion leading to anaerobic metabolism and lactate production.
Methane intoxication (option a) is not a recognized cause of metabolic acidosis in clinical practice.
Clinical Context
The most common mechanisms leading to non-anion gap metabolic acidosis include 2:
- Loss of large quantities of base secondary to diarrhea
- Administration of large quantities of chloride-containing solutions in treatment of hypovolemia and shock states
Important Caveats
- While guidelines acknowledge the association between normal saline resuscitation and hyperchloremic acidosis, studies in pediatric populations showed mixed results, with some demonstrating pH changes (7.36 to 7.32) while others found no significant effect on acid-base status 1
- The clinical significance of mild hyperchloremic acidosis from saline administration remains debated, though it is well-established as the mechanism 1
- Non-anion gap acidosis can be confirmed by calculating anion gap: Na+ + K+ - Cl- - HCO3-, which should be normal (typically <12-16 mEq/L) 4