Day #23 - Rhabdomyolysis

Today the discussant provided a broad and comprehensive approach to bilateral leg weakness and using the clinical clues of bilateral leg pain (thigh/calf), inabilty to ambulate, and pseudohematuria we arrived at the diagnosis of rhabdomyolysis.

Causes of Rhabdomyolysis Include:

1) Toxins

• Direct myotoxins: statins (particularly with fibrates), corticosteroids, some antifungals/antibiotics
  
• Indirect myotoxins: alcohol, benzodiazepines, cocaine, ecstasy, methamphetamines, LSD, paralytic agents, carbon monoxide
  

2) "Trauma"

• Prolonged immobility, crush, electrocution
• Post exertional: marathon, overexertion in the "unfit"
  
• Heat stroke, Neuroleptic malignant syndrome, malignant hyperthermia

3) Metabolic

• Hyper/hyponatremia, hypokalemia, hypophosphatemia, hypocalcemia, hyper/hypothyroid
• Genetic abnormalities in lipid, carbohydrate or purine metabolism
  

4) Inflammatory/Infectious (viral including HIV, parasitic, other)

Treatment of Rhabdomyolisis:

• Remove precipitant if possible
• Fluids, Fluids, Fluids -- Litres of Normal Saline or other fluid will be required, usually at rates up to 250-500cc/hr after initial boluses. The goal is to correct any existing pre-renal azotemia, see the CK decrease to <1,000>
• Watch for electrolyte abnormalities and correct them! In particular life threatening hyperkalemia can occur.
  
• Watch for compartment syndrome

Though there are biologically plausible reasons, there is an absolute paucity of evidence in favor of urine alkalinization. It is likely that adequate volume replacement is much more important than alkalinization. There are several caveats to attempting to alkalinize the urine including:

• Development of significant metabolic alkalosis (perhaps severe)
• Potential for hypokalemia and hypocalcemia
  

If you are going to try to alkalinize the urine you should use 3AMPS of HCO3 in 850cc D5W to make a solution that is relatively isotonic to normal saline and then run it at adequate rates to volume rescucitate the patient. Your goal is to make the urine alkaline (pH >=7) while keeping the serum pH < 7.6 (ideally <7.55).

There is also a paucity of evidence for forced diuresis with mannitol or furosemide and I would not recommend it unless you need to because of volume overload. In that case, perhaps early hemodialysis would be superior.