Acute or chronic metabolic acidosis with or without coma (including diabetic ketoacidosis). Renal failure, severe renal or hepatic impairment, acute conditions which may affect renal function e.g. dehydration, severe infection or shock. Cardiac failure, CHF, IDDM, severe impairment of thyroid function; acute or chronic alcoholism. Acute or chronic diseases which may cause tissue hypoxia e.g. cardiac or respiratory failure, recent MI or shock. Pregnancy, lactation.