Oliguria, characterized by an hourly urine output below 0.5 cc per kilogram of body weight or a daily urine output less than 400 cc, is a common clinical problem. Early recognition and successful diagnosis are required to promptly initiate appropriate therapy and to limit the risk of renal failure. While there are a number of potential causes for this condition, one important etiology to consider (especially in postoperative patients and trauma victims) is rhabdomyolysis, a condition that often progresses to myoglobinuric acute renal failure.

Rhabdomyolysis is defined by an excessive breakdown of striated muscle. When this occurs, cellular materials (including a number of muscle-specific enzymes) are released into the bloodstream. Elevated blood levels of creatine kinase, as well as lactate dehydrogenase or aldolase, are often used to confirm the diagnosis. Myoglobin, an oxygen-carrying hemeprotein found in muscle cells, also enters the bloodstream during rhabdomyolysis. Following excessive muscle injury, the blood is unable to bind and clear the increased myoglobin load, which is then excreted by the kidneys. When urinary myoglobin becomes elevated, patients develop dark, tea-colored urine characteristic of myoglobinuria.

Most clinicians are able to recognize the common risk of rhabdomyolysis in trauma scenarios with extremity ischemia, reperfusion injury, compartment syndrome, crush injury, substantial blunt trauma, or electrical injury. Identification in postoperative patients, on the other hand, is more difficult. Positioning during prolonged surgical procedures has been well described in association with rhabdomyolysis and myoglobinuric renal failure. Whether related to nonsupine positions (lithotomy or lateral decubitus) or suboptimal padding (hard tables or back boards), muscle compression of any etiology impairs perfusion and ischemic injury is likely to occur. Morbidly obese are also at increased rate of developing significant muscle injury because of excessive pressure and often extended operative times. Likewise, muscle injury from malignant hyperthermia and prolonged paralysis (often in conjunction with steroid use) can result in
rhabdomyolysis. Therefore, specific at-risk populations should be routinely screened to ensure prompt diagnosis. The astute clinician will also recognize that the inciting event for rhabdomyolysis can be as minimal as compressions delivered by sequential compression devices.