Lactic acidosis is a medical condition characterized by a build-up of lactate (especially -lactate) in the body, with formation of an excessively low pH in the bloodstream. It is a form of metabolic acidosis, in which excessive acid accumulates due to a problem with the body's oxidative metabolism. Lactic acidosis is typically the result of an underlying acute or chronic medical condition, medication, or poisoning. The symptoms are generally attributable to these underlying causes, but may include nausea, vomiting, Kussmaul breathing (laboured and deep), and generalised weakness. The diagnosis is made on biochemical analysis of blood (often initially on arterial blood gas samples), and once confirmed, generally prompts an investigation to establish the underlying cause to treat the acidosis. In some situations, hemofiltration (purification of the blood) is temporarily required. In rare chronic forms of lactic acidosis caused by mitochondrial disease, a specific diet or dichloroacetate may be used. The prognosis of lactic acidosis depends largely on the underlying cause; in some situations (such as severe infections), it indicates an increased risk of death. Classification The Cohen–Woods classification categorizes causes of lactic acidosis as: Type A: Decreased tissue oxygenation (e.g., from decreased blood flow) Type B B1: Underlying diseases (sometimes causing type A) B2: Medication or intoxication B3: Inborn error of metabolism Signs and symptoms Lactic acidosis is commonly found in people who are unwell, such as those with severe heart and/or lung disease, a severe infection with sepsis, the systemic inflammatory response syndrome due to another cause, severe physical trauma, or severe depletion of body fluids. Symptoms in humans include all those of typical metabolic acidosis (nausea, vomiting, generalized muscle weakness, and laboured and deep breathing). Causes The several different causes of lactic acidosis include: Genetic conditions Biotinidase deficiency, multiple carboxylase deficiency, or nongenetic deficiencies of biotin Diabetes mellitus and deafness Fructose 1,6-bisphosphatase deficiency Glucose-6-phosphatase deficiency GRACILE syndrome Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes Pyruvate dehydrogenase deficiency Pyruvate carboxylase deficiency Leigh syndrome Drugs Linezolid Paracetamol/acetaminophen poisoning Metformin: this risk is low (less than 10 cases for 100,000 patient years), but the risk of metformin-induced lactic acidosis (MALA) increases in certain situations where both the plasma levels of metformin are increased and lactate clearance is impaired. The older related and now withdrawn drug phenformin carried a much higher risk of lactic acidosis. Isoniazid toxicity Propofol Epinephrine Propylene glycol (D-lactic acidosis) Nucleoside reverse-transcriptase inhibitors Abacavir/dolutegravir/lamivudine Emtricitabine/tenofovir Potassium cyanide (cyanide poisoning)