Metabolic Acidosis
February 15th, 2021
Overview
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
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