Rhabdomyolysis

Background

Muscle necrosis and the release of intracellular muscle constituents into the circulation

DDx

Colored Urine (DDx)

Causes

Trauma or muscle compression
1. Crush injury
2. Immobilization
3. Compartment syndrome
Nontraumatic exertional
1. Exercise + hot weather
2. Exercise + sickle cell
3. Exercise + hypokalemia
4. Hyperkinetic states
  1. Seizure
  2. DTs
  3. Stimulant overdose
  4. Malignant hyperthermia
  5. NMS
Nontraumatic nonexertional
1. Drugs and toxins
  1. Coma induced by sedatives
  2. Statins
  3. Colchicine
  4. CO poisoning
2. Infection
  1. Viral myositis - Influenza, Coxsackie, EBV, HSV, HIV, CMV
  2. Bacterial pyomyositis
  3. Septicemia
3. Endocrine
  1. Hypothyroidism
4. Inflammatory myopathies
  1. Moderate CK elevations only (rhabdo only described in case reports)
5. Miscellaneous
  1. Status asthmaticus
  2. TSS
  3. Mushroom ingestion

Workup

Investigate cause
Total CK
CBC
Chem 10
UA
LFTs
PT/PTT
Urine pH
Ionized Ca
Consider ABG

Follow

1. Urine pH
2. Potassium

Diagnosis

Clinical

Instigating cause
Myalgias
1. May progress to weakness
Red/brown "tea colored" urine
Renal failure

Laboratory

Elevated Total CK (no defined threshold)
1. >5-10K (injury possible)
  1. Normally associated with co-existing conditions (e.g. sepsis + chronic myopathies)
2. >15-20K (injury more likely)
3. CK-MB may be entirely normal or may be mildly elevated (reflects small amount found in skeletal tissue)
Myoglobinuria
1. UA = +blood, but no RBCs
  1. Sensitivity = 80% (for rhabdo)
2. Is cleared much faster than CK (may see elevated CK with no myoglobinuria)
3. Is pathognomonic
Transaminitis
Creatinine increase (if renal failure)
Electrolyte Abnormalities
1. Hyperkalemia
2. Hyperphosphatemia
3. Hypocalcemia
4. Hyperuricemia
5. Metabolic acidosis

Treatment

Aggressive IVF
1. Start with 1-2 L/hr
2. Once diuresis occurs maintain urine output of 200-300 mL/hr (3mL/kg)
3. Frequently need ~10 L/day
Bicarb^
1. Indication = Urine pH is <6.5
2. After initial IVF, give 75mmol NaHCO3 in 1L 1/2NS
  1. Alternative regimen = 100mmol NaHCO3 in 1L 1/2NS, alternated with 1L NS (no NaHCO3), repeat
  2. Goal urine pH is >6.5
  3. Monitor for hypocalcemia closely!
  4. If urine pH is not > 6.5 after 3-4 hrs or symptomatic hypocalcemia results d/c
Mannitol^^
1. Consider if unable to establish diuresis after significant volume repletion
  1. Must check plasma osmolaity and plasma osmolal gap q4-6hr
  2. D/c if osmolal gap > 55 mosmol/kg
  3. If mannitol establishes diuresis, continue until urine discoloration clears and CK decreases to <10K

^Degrees of controversy

Complications

Acute Renal Failure
Hyperkalemia
1. Treat aggressively
Hypocalcemia (initial phase)
1. Treat only if symptomatic or severely hyperkalemic (pts often have rebound hypercalcemia)
Hypercalcemia (recovery phase)
Hyperphosphatemia
1. Treat cautiously (treatment may worsen calcium precipitation in muscle)

Evidence Based Questions

No randomized, controlled trial has supported the evidence-based use of mannitol, and some clinical studies suggest no beneficial effects. In addition, high accumulated doses of mannitol (>200 g per day or accumulated doses of >800 g) have been associated with acute kidney injury due to renal vasoconstriction and tubular toxicity, a condition known as osmotic nephrosis. However, many experts continue to suggest that mannitol should be used to prevent and treat rhabdomyolysis-induced acute kidney injury and relieve compartmental pressure. During the time mannitol is being administered, plasma osmolality and the osmolal gap (i.e., the difference between the measured and calculated serum osmolality) should be monitored frequently and therapy discontinued if adequate diuresis is not achieved or if the osmolal gap rises above 55 mOsm per kilogram.

A. Bozch X et al. Rhabdomyolysis and Acute Kidney Injury. NEJM 2009; 361: 62-72

Source

KajQuestions

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