Defined as an arterial blood pH <7.35 with plasma HCO3 <22 mmol/L

Respiratory compensation occurs normally immediately, unless there is respiratory pathology. Pure metabolic acidosis is a term used to describe when there is not another primary acid-base derangement - ie there is not a mixed acid-base disorder. Compensation may be partial (very early in time course, limited by other acid-base derangements, or the acidosis exceeds the maximum compensation possible) or full.

Causes

• Usually according to the anion gap
  • (Na+ K) - (Cl+ HCO). Normal range is 10-18

Normal anion gap ( = hyperchloraemic metabolic acidosis)

• Addison's disease
• bicarbonate (GI) loss: diarrhoea, ureterosigmoidostomy, fistula
• Chloride excess
• diuretics
• renal tubular acidosis
• ammonium chloride injection

Raised anion gap

• lactate: shock, sepsis, hypoxia
• ketones: diabetic ketoacidosis, alcohol
• uraemia: renal failure
• acid poisoning: salicylates, methanol

Metabolic acidosis secondary to high lactate levels may be subdivided into two types: