Oliguria and a rise in the plasma urea concentration are normal physiological responses to the haemodynamic changes associated with hypovolaemia, cardiac failure, or sepsis. Clinical decision making during the ensuing hours may determine whether a patient makes a speedy recovery or develops the serious complication of established acute renal failure. This condition still has a mortality of about 50%, despite recent improvements in clinical practice.1 A meta-analysis in this week's BMJ by Ho and Sheridan reviews the evidence on one commonly used and cheap intervention—the loop diuretic furosemide (frusemide)—but finds it to be of little use in preventing or treating acute renal failure.2

Acute renal failure occurs in a variety of different circumstances and can complicate pre-existing chronic renal failure. The traditional split into prerenal, renal, and postrenal causes of acute failure is useful, if only to remind doctors of the need for a systematic approach to diagnosis and management of the underlying cause. It is appropriate that prerenal causes come first, …