Crush Injury Syndrome: Rhabdomyolysis Recognition and Response

The Pathophysiology

Normal muscle cells maintain a massive intracellular concentration of potassium, phosphate, and myoglobin (the oxygen-carrying protein in muscle, similar to hemoglobin in blood). Under prolonged compression, cells die from ischemia (lack of blood flow) and the cell membranes fail.

When compression is released and blood flow returns:

1. The intracellular contents of millions of dead muscle cells flood the bloodstream simultaneously
2. Myoglobin reaches the kidneys and precipitates in the tubules — it is directly toxic and creates tubular obstruction — causing acute tubular necrosis (kidney failure)
3. Potassium releases massively — hyperkalemia causes cardiac arrhythmias, including fatal ventricular fibrillation
4. Phosphate releases — hyperphosphatemia causes hypocalcemia (low calcium), which further predisposes to arrhythmias
5. Fluid shifts — damaged muscle tissue acts like a sponge, pulling massive amounts of fluid from the circulation into damaged muscle compartments, causing hypovolemic shock

This is why a person can be talking to rescuers from under debris and then die from cardiac arrest or renal failure within hours of rescue. The injury is not the physical trauma — it is the reperfusion chemistry.

Who Is at Risk

Any patient with:

• Large muscle groups compressed for > 1 hour (thigh, lower leg, gluteal muscles particularly)
• Prolonged entrapment under building collapse, vehicle pinning, landslide
• Extended pressure on a limb from lying immobile (drunk, unconscious, posturing after stroke)
• High-voltage electrical injury (causes direct muscle destruction)
• Extreme physical exertion in untrained individuals combined with dehydration (exertional rhabdomyolysis)

The greater the muscle mass compressed and the longer the duration, the worse the syndrome.

Recognition

During Entrapment

• Determine compression duration
• Assess for extremity edema beyond the compression site (swollen limb)
• Patient may complain of numbness or tingling (compartment syndrome developing)
• Skin may show pressure marks, marbling, or mottling

After Release: Watch For

Early signs (first 1-12 hours):

• Tea-colored, dark brown, or red-brown urine — this is myoglobinuria (myoglobin in urine). This is a major warning sign. Normal urine after crush injury is alarm-negative; dark urine means significant rhabdomyolysis.
• Decreasing urine output despite fluid intake
• Swelling and extreme tenderness of the compressed extremity
• Muscle weakness in the affected limb

Signs of hyperkalemia (cardiac emergency):

• Cardiac monitor (if available): peaked T-waves, widening QRS, sine wave pattern, ventricular fibrillation
• Without monitor: unexplained cardiac arrest in crush victim always suspect hyperkalemia

Signs of hypovolemia/shock:

• Tachycardia, hypotension
• The compressed limb can sequester 3-5 liters of fluid from the circulation

Signs of compartment syndrome (see separate consideration):

• Severe pain in the affected limb, especially with passive stretch of muscles
• Woody hardness of the compartment

Signs of developing renal failure (later, hours to days):

• Decreasing urine output progressing to oliguria (< 400ml/day) or anuria
• Nausea, vomiting, confusion (uremia)

Treatment

Fluid Resuscitation: The Most Critical Intervention

Goal: Maintain urine output at 200-300ml/hour until urine clears. This is a very high urine output target — roughly 3× normal. The goal is to flood the kidneys with dilute urine to prevent myoglobin from precipitating in the tubules.

Rate: Start at 1 liter per hour intravenously, continuing until urine output target is achieved and urine color clears.

Total volume: In the first 24 hours, 6-10 liters of IV fluid is not unusual in significant crush syndrome. This is much more than standard trauma resuscitation.

If IV not available: Push oral fluids as fast as the patient can tolerate (a liter per hour of water or ORS is the target). This is inadequate compared to IV but provides some protection.

Fluid type: Normal saline (0.9% NaCl) or Lactated Ringer's. The choice has been debated — both work. Avoid hypotonic fluids (0.45% saline).

Sodium bicarbonate: Clinical recommendation varies, but many protocols add sodium bicarbonate to IV fluid (1-2 ampules of 50 mEq NaHCO3 per liter) to alkalinize the urine — alkaline urine reduces myoglobin precipitation. If bicarbonate is available: use it. If not, normal saline alone is still highly beneficial.

Urine Monitoring

Check urine color frequently. Dark brown/red urine means myoglobin is still being cleared. Clear or slightly yellow urine means myoglobin is being adequately flushed.

If urine output drops despite adequate fluid intake: the kidneys may be failing. Continue fluids (if kidneys have failed, continue aggressive treatment, but acknowledge that dialysis will be needed — evacuation is urgent).

Hyperkalemia Management (Cardiac Emergency)

If you have ECG monitoring and see peaked T-waves or widened QRS in a crush victim, assume hyperkalemia.

Without ECG monitoring: If a crush victim with > 4 hours of compression develops cardiac arrhythmia or cardiac arrest, hyperkalemia is a probable contributing cause.

Treatment in field settings (limited options):

• Calcium gluconate or calcium chloride IV (if available): stabilizes cardiac membrane within minutes. Does not lower potassium but protects the heart while other measures work.
• Sodium bicarbonate IV: shifts potassium from blood into cells (temporary reduction, buys time)
• Albuterol nebulized (if available): beta-2 stimulation drives potassium into cells
• Eliminating potassium-containing IV fluids: switch from Lactated Ringer's (contains potassium) to normal saline

Tourniquet Consideration

In crush injury, tourniquet above the entrapped limb prior to release is sometimes recommended to delay systemic release of toxic materials until IV fluids are established. This is a contested intervention and should only be considered if:

• The limb appears completely non-viable (no chance of saving it)
• IV fluids cannot be started before release
• The decision is made collaboratively by trained providers

A tourniquet applied to a potentially salvageable limb in a crush victim causes irreversible ischemia. Do not tourniquet unless the decision is made that the limb is unsalvageable.

Fasciotomy for Compartment Syndrome

Following reperfusion, pressure in the fascial compartments of the limb can exceed perfusion pressure, causing a compartment syndrome that kills the remaining living muscle. Signs: extreme pain, woody-hard firmness of the compartment, pain with passive stretch of muscles in the compartment.

Fasciotomy — surgical release of the fascial compartment — is the definitive treatment. This is a surgical procedure requiring training. In a true austere setting with no possible evacuation and obvious compartment syndrome progressing to limb loss:

• A longitudinal incision through the skin and fascia along the compartment can release pressure
• This is a surgical procedure with significant risks (infection, bleeding) and should only be attempted by trained providers when the alternative is certain limb loss
• Most field settings should evacuate rather than attempt fasciotomy

Evacuation Priority

Crush syndrome with evidence of myoglobinuria (dark urine) or hyperkalemia is a medical emergency requiring ICU-level care: continuous IV fluids, cardiac monitoring, dialysis capability, and ICU nursing.

Patients with crush syndrome can appear deceptively stable for hours before deteriorating rapidly. Evacuation should not wait for clinical deterioration — it should be based on mechanism and myoglobinuria.