Anion gap metabolic acidosis

Definition

• Metabolic acidosis with an increased anion gap

Differential Diagnosis

GOLDMARK

• Glycols: ethylene (AKI, osmolar gap) and propylene (osmolar gap)
• Oxoproline (acetaminophen)
• L-lactic acidosis: rapid-onset
• D-lactic acidosis: bowel stasis
• Methanol: visual changes, osmolar gap
• ASA
• Renal failure
• Ketoacidosis

Biochemical Approach

• Lactic acidosis
  • Type A: impaired tissue oxygenation
    • Systemic hypoperfusion and shock
  • Type B
    • Metformin
    • Malignancy
    • Chronic alcohol intake (mild)
    • HIV medications
    • IV epinephrine
    • Mitochondrial dysfunction
    • Propofol
    • Linezolid
  • D-lactaic acidosis: short bowel syndrome
• Ketoacidosis
  • Diabetic ketoacidosis (DKA)
  • Alcoholic ketoacidosis
  • Starvation
• Toxins
  • Salicylates
  • Acetaminophen (5-oxoproline)
  • Methanol (formic acid)
  • Ethylene glycol (glycolic acid and oxalic acid)
• Renal failure (acute or chronic)

Clinical Presentation

• Rapid onset: lactic acidosis
• Osmolar gap: methanol, ethanol, ethylene glycol
• Visual changes: methanol
• AKI: ethylene glycol
• Normal pH: ethanol
• Slow bowel transit: D-lactic acidosis

Investigations

• Serum electrolytes
  • Anion gap
  • Delta-delta: increase in anion gap should be matched by equal decrease in bicard
• Serum osmolarity
• Lactate, to rule out lactic acidosis

Management

• Treat underlying cause