Lactate is produced by glycolysis and normally cleared by the liver and kidneys. When production outpaces clearance, or when liver function is impaired, lactate accumulates, causing an increased anion gap metabolic acidosis. Conditions leading to lactate accumulation include shock, sepsis, cardiogenic failure, severe anemia, respiratory failure, liver disease, and certain medications or toxins. Alcohol use, metformin, linezolid, nucleoside reverse transcriptase inhibitors, and thiamine deficiency are notable contributors in some patients. Mitochondrial disorders and other inborn errors can also cause lactic acidosis.
Clinical features depend on the underlying cause and the degree of acidosis. Patients may present with rapid breathing (often compensatory), malaise, nausea, abdominal pain, confusion, seizures, or signs of shock and organ dysfunction in severe cases.
Diagnosis is made from laboratory findings showing a high anion gap metabolic acidosis with elevated lactate. Lactate is typically considered elevated above about 2 mmol/L, with higher values indicating more severe disease and poorer prognosis. Additional testing includes arterial or venous blood gas, glucose, liver and kidney function, and sometimes the lactate-to-pyruvate ratio to help distinguish causes.
Management focuses on treating the underlying cause and supporting perfusion and oxygen delivery. Fluid resuscitation and vasopressors for shock, oxygenation, and avoidance of further lactate production are central. Offending drugs should be stopped; thiamine may be given if deficiency is suspected. Bicarbonate therapy is controversial and usually reserved for severe acidosis (pH around 7.1 or lower). In metformin-associated lactic acidosis or severe cases, renal replacement therapy may be used to remove lactate and the offending agent. Prognosis depends on the underlying illness and the degree of organ dysfunction. Lactic acidosis commonly occurs in critically ill patients and carries significant mortality risk when associated with shock or multi-organ failure.