Anion gap acidosis

Clinical Features

• Signs/symptoms of underlying disease
• Compensatory tachypnea

Differential Diagnosis

Anion gap metabolic acidosis

• Lactic acidosis
  • Sepsis, shock, liver disease, CO, CN, metformin, methemoglobin
  • Short bowel syndrome
  • Propylene glycol infusions for lorazepam and phenobarbital
• Renal failure
  • Uremia
• Ketoacidosis
  • DKA
  • Alcoholic Ketoacidosis
  • Starvation ketoacidosis
• Ingestions
  • Acetaminophen toxicity
  • Aspirin toxicity
  • Increased osm gap
    • Methanol
    • Ethylene glycol
  • Normal osm gap
    • Salicylate toxicity
    • Iron
    • INH

Evaluation

• AG = Na - (Cl + HCO3)
• Normal Anion Gap = 12+/-4 (8-16)
• 12-20 mEq/L when including K+
• Primary acidosis if pH <7.38
• HCO3 <24 = metabolic acidosis
• Always determine if there is another acid/base process occurring
  • Primary respiratory acidosis if pCO2 > pCO2expected
  • Primary respiratory alkalosis if pCO2 < pCO2expected
    • use Winter's formula: PCO2 (expected) = (1.5 x [HCO3–] + 8) ± 2
    • In acute setting PCO2 should fall by 1 mmHg for every 1 mEq fall in HCO3
  • Concurrent metabolic alkalosis if delta-delta > 28
  • Delta-Delta = (AG - 12) + HCO3

Management

• Treat source
• Correct any respiratory acidosis
• Bicarbonate
  • HCO3 dose in mEq = 0.5(wt in kg) x (24 - measured HCO3)
  • Each bicarb 0.5mEq/kg causes 1 meq/L rise in HCO3
  • Consider for:
    • Bicarb <4
    • pH <7.20 AND shock/myocardial irritability
    • Severe hyperchloremic acidemia
      • Lost bicarbonate would take days to replenish

See Also

• Non anion gap acidosis