Metabolic acidosis

  • What is metabolic acidosis?
  • What are the causes?


Metabolic acidosis

What is metabolic acidosis?

Metabolic acidosis occurs when an acid other than carbonic acid (due to CO2 retention) accumulates in the body, resulting in a fall in the plasma bicarbonate.


* Davidson’s Principles and Practice of Medicine, 22nd edition Page 445
What are the causes of metabolic acidosis?

Causes of metabolic acidosis

Disorder Mechanism
A. Normal anion gap**
Ingestion or infusion of inorganic acid Therapeutic infusion of or poisoning with NH4Cl, HCl
Gastrointestinal HCO3 loss Loss of HCO3 in diarrhoea, small bowel fistula, urinary diversion procedure
Renal tubular acidosis (RTA) Urinary loss of HCO3 in proximal RTA; impaired tubular acid secretion in distal RTA
B. Increased anion gap
Endogenous acid load
Diabetic ketoacidosis Accumulation of ketones1 with hyperglycaemia
Starvation ketosis Accumulation of ketones without hyperglycaemia
Lactic acidosis Shock, liver disease, drugs
Renal failure Accumulation of organic acids
Exogenous acid load
Aspirin poisoning Accumulation of salicylate2
Methanol poisoning Accumulation of formate
Ethylene glycol poisoning Accumulation of glycolate, oxalate
1Ketones include acid anions acetoacetate and β-hydroxybutyrate
2Salicylate poisoning is also associated with respiratory alkalosis due to direct ventilatory stimulation.

**Anion gap = Difference between the main measured cations (Na+ + K+) and the anions (Cl + HCO3). This ‘gap’ is normally around 12–16 mmol/L (12–16 meq/L)

* Davidson’s Principles and Practice of Medicine, 22nd edition Page 445
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