Oliguria is a common clinical finding in the postoperative and posttrauma patient. The introduction of the loop diuretics, ethacrynic acid and furosemide, has provided an effective method for inducing an increased urine flow under these circumstances. These agents are so effective that they may induce a large loss of fluid and electrolytes, which will be detrimental to the patient's condition. Precisely because they are effective, there has been a tendency to omit the careful evaluation of the patient's clinical state that would lead to a correct interpretation of the cause of oliguria and its specific therapeutic correction.
With very few exceptions, the cause of postoperative and posttraumatic oliguria is oligemia or depletion of the extracellular fluid volume. This is especially true within the first few hours after surgery or trauma, when irreversible tubular damage is rarely, if ever, present. If mechanical obstruction to the upper or lower urinary tract has