Lactate
Formal Definition
Serum lactate: a metabolic byproduct of anaerobic glycolysis that accumulates when tissue oxygen delivery is inadequate, used as a marker of tissue hypoperfusion and disease severity in critically ill patients.
How It's Used on the Ward
"Lactate is up" or "clear the lactate" — elevated lactate flags occult shock even when blood pressure appears normal.
Example
""BP 110/70, looks okay — but lactate 4.8 on arrival. Cryptic sepsis: aggressive fluid resuscitation, cultures, broad antibiotics, ICU bed requested. Don't be fooled by a normal BP.""
Clinical Context
Lactate > 2 mmol/L = concerning. Lactate > 4 mmol/L with suspected infection meets Sepsis-3 septic shock criteria regardless of blood pressure. Serial lactate clearance (>10% reduction per hour) is a target of sepsis resuscitation. Elevated lactate ≠ always lactic acidosis — check pH. Causes beyond shock: liver failure (impaired clearance), thiamine deficiency (type B lactic acidosis), metformin toxicity.