Type A & B Lactic Acidosis
What it is
Lactic acidosis describes raised blood lactate with an anion‑gap metabolic acidosis. In the ED, lactate is used as a marker of inadequate tissue oxygen delivery and as a prognostic/monitoring tool. Clinically the term is split into:
- Type A - due to tissue hypoxia/hypoperfusion (anaerobic glycolysis).
- Type B - not caused by global hypoxia; from impaired lactate clearance, metabolic derangement, or toxins that disrupt cellular oxidative metabolism (histiotoxic hypoxia).
Pathophysiology (concise)
Under normal aerobic conditions, pyruvate enters mitochondria. When oxygen delivery or mitochondrial oxidative function is impaired, pyruvate is shunted to lactate.
- Type A reflects reduced oxygen delivery or extraction (shock, cardiac arrest, severe anaemia, respiratory failure).
- Type B reflects impaired clearance (liver/renal failure), co‑factor deficiency (thiamine), or toxins/drugs that block mitochondrial respiration (cyanide, biguanides, some toxic alcohols).
When to suspect lactic acidosis Suspect raised lactate in any unexplained high anion‑gap metabolic acidosis or in patients with:
- Shock (sepsis, haemorrhage, cardiogenic or obstructive), cardiac arrest, or severe LV failure.
- Severe anaemia, respiratory failure, or major airway obstruction.
- Smoke inhalation, enclosed‑space exposure, or industrial toxin ingestion.
- Metformin use with acute kidney injury (AKI), chronic alcohol misuse, malnutrition, or diabetic ketoacidosis/alcoholic ketoacidosis.