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Related Subjects: |Metabolic acidosis |Aspirin or Salicylates toxicity |Ethylene glycol toxicity |Renal Tubular Acidosis |Lactic acidosis |Metabolic alkalosis

Analysis of Metabolic acidosis Blood gas

• pH < 7.35 unless corrected
• HCO₃ < 22 mmol/L
• PaCO₂ is low due to hyperventilation to blow off CO₂ to less than 5.33 KPa
• PaO₂ usually normal
• Base Excess < -2

Aetiology

• Accumulation of Organic and Inorganic Acids or Loss of Bicarbonate HCO₃
• Anion gap = ([Na⁺ + K⁺] - [HCO₃⁻ + Cl⁻]) more than 12 mmol/L.

Clinical

• Hyperventilation with Kussmaul's breathing
• The cause is often evident but the AG helps eliminate some causes

Raised Anion Gap > 12 Acid other than HCl

• Lactic acidosis: Lactate, D-lactate acidosis, Types A & B
• Diabetic Ketoacidosis: Beta-hydroxybutyrate, acetoacetate
• Alcoholic ketoacidosis: seen with alcoholic and starvation and pancreatitis
• Renal failure/Uraemia: Sulphate, phosphate, urate, and Hippurate
• Ingestions : Salicylate, methanol or formaldehyde (formate), ethylene glycol (glycolate, oxalate), paraldehyde (organic anions), sulphur (SO4-), phenformin/metformin, propylene glycol
• Massive rhabdomyolysis (release of H⁺ and organic anions from damaged muscle)

Normal Anion Gap < 12

• Renal Tubular acidosis
• Diarrhoeal illness
• Ammonium chloride
• Acetazolamide
• Gastrointestinal loss of HCO₃⁻, eg, diarrhoea
• Pancreatic ileostomy or ileal loop bladder
• Hyperalimentation, Obstructed ileal loop
• Hypoaldosteronism (i.e. type 4 RTA)
• Recovery from diabetic ketoacidosis
• Chloride retention or administration of large amount of HCl equivalent or NH4Cl
• Dilutional acidosis from rapid administration of 0.9% NaCl