Metabolic Acidosis | ABG Interpretation - MedSchool
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ABG Interpretation
ABG Interpretation
Metabolic acidosis is a process in which an external agent or internal process is causing excessive acidity in a way that is metabolic (i.e. non-respiratory).

Metabolic Acidosis



  • Metabolic acidosis is a process in which an external agent or internal process is causing excessive acidity in a way that is metabolic (i.e. non-respiratory).
    • Look For

    • Acidaemia with reduced bicarbonate.
    • Expected Compensation

    • Decrease in PaCO₂ = 1.5 x HCO₃ + 8
    • Causes of Metabolic Acidosis

    • Ingestion of acid - methanol, ethylene glycol, salicylic acid
    • Acid production - lactic acidosis, ketoacidosis, rhabdomyolysis
    • Reduced acid excretion - renal failure, distal RTA
    • Loss of alkali - diarrhoea, proximal RTA
    • Approach

    • Check the anion gap to further distinguish between causes.

High Anion Gap Metabolic Acidosis

  • Metabolic acidosis with raised anion gap.
    • Causes of High Anion Gap Metabolic Acidosis

    • Endogenous

    • Lactic acidosis
    • Ketoacidosis - diabetic, alcoholic
    • Uraemia (end-stage renal failure)
    • Exogenous

    • Methanol / ethanol / ethylene glycol
    • Salicylates
    • Cyanide
    • Carbon monoxide

Normal Anion Gap Metabolic Acidosis

  • Metabolic acidosis without raised anion gap.
    • Causes of Normal Anion Gap Metabolic Acidosis

    • GI loss - diarrhoea, fistula, stoma
    • Isotonic saline infusion
    • Renal tubular acidosis (proximal)
    • Acetazolamide
    • Addison's Disease
Last updated on February 7th, 2020


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