Type A from hypoperfusion, type B without it
Expansion
Type A, with tissue hypoperfusion or hypoxia
- Shock of any cause: septic, hypovolaemic, cardiogenic, obstructive
- Regional ischaemia: mesenteric ischaemia, limb ischaemia, compartment syndrome, necrotising infection. These are the ones missed, because the patient may look otherwise well with a normal blood pressure
- Severe anaemia, severe hypoxia, carbon monoxide poisoning, cardiac arrest
Type B, without hypoperfusion
- B1, underlying disease: liver failure (reduced clearance), malignancy, thiamine deficiency, phaeochromocytoma, diabetic ketoacidosis
- B2, drugs and toxins: metformin, beta agonists (salbutamol infusions and nebulisers), adrenaline, linezolid, antiretrovirals, propofol infusion syndrome, alcohol, cyanide, paracetamol
- B3, inborn errors of metabolism
Other explanations for a raised value: seizures and vigorous muscular activity, which resolve within an hour; a tourniquet or a clenched fist during sampling; and D-lactate in short bowel syndrome, which the standard assay does not measure and which presents with encephalopathy and a high anion gap acidosis.
Prognostic use: lactate correlates with mortality in sepsis and trauma, and lactate clearance, meaning the fall over the first 2 to 6 hours of treatment, is a better guide to resuscitation than any single value.
A normal lactate does not exclude serious illness, particularly early mesenteric ischaemia, and a lactate raised by salbutamol in an asthma attack should not be misinterpreted as sepsis; the clinical context always governs.