Rhabdomyolysis

Etiologies:

Trauma and Muscle Compression – most common cause: Crush injuries, prolonged immobilization (usually with an obtunded state), struggling against restraints, and compartment syndrome.
Nontraumatic exertional – Seizures, DTs, psychotic agitation, extreme physical exertion
Other causes: Drugs – statins, fibrates, illicit drugs (methamphetamines, cocaine, heroin), alcohol, and idiosyncratic reactions (NMS, Malignant hyperthermia); Infections (viral, bacterial from strep/staph); Severe hypokalemia/hypophosphatemia; Ischemia to a limb due to arterial embolism; Inflammatory myopathies (dermatomyositis, polymyositis); and Congenital myopathies.

Complications of Rhabdomyolysis:

Acute Kidney Injury – can be devastating. Due to toxic effect of myoglobin. Despite ATN-like pathophysiology, classically has FeNa <1%.
Release of muscle cell constituents à Hyperkalemia, Hyperphosphatemia, Hypocalcemia (due to precipitation of CaPO4 crystals, also influx of Ca into muscle cells), Hyperuricemia (can contribute to renal failure), Anion gap metabolic acidosis (due to release of H+ and phosphate and sulfates)
Compartment syndrome – as above

Management:
Mainstay = Aggressive IVFs with the goal of maintaining a UOP of 200-300 cc/hr – they can be severely volume depleted due to sequestion of water in muscle cells. For example, our patient required ~7 liters before starting to have a good UOP. Initially, isotonic saline is fine, but there is some argument for use of bicarbonate for maintenance fluids. Urinary alkalinization may help prevent heme-protein precipitation and pigment cast formation, among other things. There is not great evidence for this, but many experts still recommend it.
For Bicarbonate, remember how to give it: 1 amp NaHCO3 = 50 meq Na and 50 meq HCO3 (in 50 cc)
--> Main Options:

D5w + 3 amps NaHCO3 --> 150 meq of Na = isotonic fluid
D5w ½ NS + 1.5 amps NaHCO --> ~152 meq of Na = isotonic fluid

DO NOT GIVE NS + 3 amps NaHCO3 AS THIS IS SUPER-HYPERTONIC AND CAN CAUSE PROBLEMS!
If adequate dieresis is not achieved despite volume repletion, you can consider diuresis with mannitol, although again there is not great evidence.

(Chanu Rhee MD, 10/14/10)