LACTIC ACIDOSIS Definition Severe lactic acidosis is defined as a high anion gap metabolic acidosis (anion gap >10, as calculated using equation in box 1) with a blood lactate concentration .5.0 mmol/l (normal 0.4–1.2 mmol/l). The pathological elevation of lactate and hydrogen ions may result from overproduction or delayed clearance of lactate, or a combination of both.