Rhabdomyolysis
Skeletal muscle necrosis floods the circulation with creatine kinase, myoglobin, potassium and phosphate: myoglobin obstructs and poisons the renal tubules, while potassium can stop the heart within hours.
Definition
Rhabdomyolysis is acute skeletal muscle necrosis with release of intracellular contents, including creatine kinase, myoglobin, potassium and phosphate, into the circulation. It is defined biochemically as an acute rise in serum creatine kinase to more than five times the upper limit of normal, with myocardial infarction excluded. Clinically significant disease carries the risks of hyperkalaemia, pigment-associated acute kidney injury and compartment syndrome.
First principles
Creatine kinase makes the diagnosis, but potassium is what kills first
Necrotic muscle leaks creatine kinase, myoglobin, potassium, phosphate and urate. Creatine kinase is the diagnostic marker: rhabdomyolysis is an acute rise to more than five times the upper limit of normal, which with a normal range of 30 to 190 units/L means anything above 950 units/L. It is a poor prognostic marker, and it is not what harms the patient. Potassium is. Release is steepest in the first 12 to 36 hours, so an acceptable potassium on arrival settles nothing.
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