Pathology of the Week – Rhabdomyolysis
Medicalese: rhabdos – rod shaped; myo – related to muscle cells; lysis – break down of cells (greek for to separate). Short forms: rhabdo.
Rhabdomyolysis occurs when certain types of muscle cells (striated ones) break down allowing their contents to spill out into the bloodstream (the extracellular space). One of the contents of the cell is myoglobin which can damage a sensitive part of the kidneys called the tubules. The blood can handle some myoglobin floating around because it binds it to proteins which are too large to fit through the porous membranes of the glomeruli. When too much myoglobin is floating around in blood plasma not all of it becomes bound to protein and some passes into the sensitive renal tubules. A part of the myoglobin, heme, accumulates in the tubules and creates casts that cause tubule death and resultant acute renal failure. I will reference nephrologist Dr. Joel Topf’s 2009 case study as well as this 2000 Van Holder et al review (free public access). See also this physical therapist oriented video.
Signs and Symptoms
Rhabdomyolysis can be caused by traumatic and non-traumatic injuries. In the case of the former a sign would be a mechanism of injury potentiating crushed muscle cells (trapped patient, etc.). In non-traumatic cases the patient may complain of muscle weakness/stiffness. Although myoglobin will become visible to the naked eye in urine at concentrations of 100 mg/L, these levels rarely rise over 25 mg/ L (Ref: Saad, E). Rhabdomyolysis leads to acute renal failure, the symptoms of which would be oliguria/anuria (reduced, or no, urine output). An adult patient is considered oliguric if they are producing less than half a litre of urine in 24h.
If muscles cells become crushed, or even just ischaemic for prolonged periods of time, their cell membranes may decay allowing myoglobin to spill into the blood stream. It was first academically documented during the blitz bombing of London in WWII from these mechanisms. Other physical causes are high-voltage electrical injuries, pyrexia and prolonged physical exercise – especially in hot, humid environments. Rhabdo can also be caused by nonphysical factors such as infections, snake/insect venom, electrolyte imbalances and various drug interactions such as cocaine, alcohol and heroine. In the case of electrolyte imbalances hypokalaemia is a particular culprit. Potassium (the kal in kalaemia) plays a role in normal muscular exertion. Muscle cells release intracellular potassium during acute periods of exertion which causes vasodilation and increased perfusion to the localized myocytes (muscle cells). With low potassium this normal bodily function is reduced.
Mangement and Treatment
If you suspect a patient is at risk for rhabdomyolysis, and subsequent renal failure, volume fluid is the most important treatment. IV fluids should be administered to correct volume depletion If the patient is already oliguric treatment is a specialized course of that for acute renal failure. Loop diuretics may help to open up the tubules and prevent ischaemia.
Implications for Prehospital Care
Rhabdomyolysis should be in the back of your mind when attending a technical rescue involving crush, collapse or cave-in injuries. Also if the patient has spent sometime hanging in free-air in a fall-arrest harness. As Vanholder et al recommend, scene safety conditions permitting, attempt to initiate IV therapy during extrication.