Metabolic acidosis is characterized by a primary reduction in serum bicarbonate (HCO(3)(-)) concentration, a secondary decrease in the arterial partial pressure of carbon dioxide (PaCO(2)) of approximately 1 mmHg for every 1 mmol/l fall in serum HCO(3)(-) concentration, and a reduction in blood pH. Acute forms (lasting minutes to several days) and chronic forms (lasting weeks to years) of the disorder can occur, for which the underlying cause/s and resulting adverse effects may differ. Acute forms of metabolic acidosis most frequently result from the overproduction of organic acids such as ketoacids or lactic acid; by contrast, chronic metabolic acidosis often reflects bicarbonate wasting and/or impaired renal acidification. The calculation of the serum anion gap, calculated as [Na(+)] - ([HCO(3)(-)] + [Cl(-)]), aids diagnosis by classifying the disorders into categories of normal (hyperchloremic) anion gap or elevated anion gap. These categories can overlap, however. Adverse effects of acute metabolic acidosis primarily include decreased cardiac output, arterial dilatation with hypotension, altered oxygen delivery, decreased ATP production, predisposition to arrhythmias, and impairment of the immune response. The main adverse effects of chronic metabolic acidosis are increased muscle degradation and abnormal bone metabolism. Using base to treat acute metabolic acidosis is controversial because of a lack of definitive benefit and because of potential complications. By contrast, the administration of base for the treatment of chronic metabolic acidosis is associated with improved cellular function and few complications.