Case 48: Dark urine
A 28 year old man was found unconscious at home after an overdose of heroin. A catheter was inserted and dark urine drained. He was not jaundiced.
1. What is the cause of this urine appearance?
Rhabdomyolysis with myoglobinuria.
2. What other specific features would you examine for?
Significant muscle necrosis may lead to compartment syndrome if the muscles involved are contained within a tight fascial compartment. There examine all muscle groups for tenderness and tenseness. Also look for pain on passive stretch of the muscles. The presence of distal pulses does not exlude compartment syndrome. If there is any concern then compartment pressures can be measured simply with a needle attached to a pressure transducer.
3. What specific investigations would you request?
Assessment of the degree of muscle necrosis can be made with measurement of the creatine kinase (CK) level. The renal function and electrolytes should also be checked as the major systemic consequence of rhabdomyolysis is renal failure.
4. Outline your plan of management for this problem?
Aggressive fluid resuscitation aiming for a urine output of 1 ml/kg/hr. Correction of electrolyte abnormalities as they are detected. Alkalinising the urine with oral or IV bicarbonate may improve the solubility of myoglobin and prevent it's deposition within the renal tubules. Liase early with a renal physician or the intensive care unit if renal replacement therapy may be required.
Any muscle compartments suspected to be developing raised pressure should be managemd with fasciotomy. If fasciotomy is not performed then the muscles should be reviewed regularly to detect development of problems early.