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Crush Syndrome: A Comprehensive Overview

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Definition

"Crush syndrome is the body's systemic manifestations caused by crushed muscle tissue, and often occurs when blood flow is restored to the crushed tissue and toxins are released in the body's circulation." - Rosen's Emergency Medicine, 10th Ed.

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Etiology

Traumatic Causes

Non-traumatic Causes of Rhabdomyolysis (that can produce a similar syndrome)

• Seizures (sustained muscle contraction)
• Strenuous exercise (exertional rhabdomyolysis)
• Heatstroke / hyperthermia
• Malignant hyperthermia
• Neuroleptic malignant syndrome
• Drugs/toxins: statins, cocaine, heroin, alcohol, amphetamines, MDMA, CO poisoning
• Infections: influenza A/B, Coxsackievirus, S. pyogenes, S. aureus pyomyositis
• Metabolic disorders: hypokalemia, hypophosphatemia, hypocalcemia, DKA
• Inherited myopathies (recurrent episodes - suspect glycolytic/lipid metabolism disorders)

Epidemiology

• Crush syndrome occurs in 2-15% of all trauma patients
• Up to 30-40% of earthquake victims and survivors of multi-story building collapses
• First recognized clinically during the London Blitz (World War II) by Bywaters and Beall, 1941

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Pathology and Pathophysiology

1. Direct Compression Injury (During Entrapment)

• External force mechanically disrupts the sarcolemma (muscle cell membrane)
• Ischemia develops as microvascular compression cuts off O2 supply
• Anaerobic metabolism generates lactic acid → metabolic acidosis
• ATP depletion disables the Na+/K+-ATPase and Ca2+-ATPase pumps

2. Ischemia-Reperfusion Injury (Upon Extrication)

• The paradoxical exacerbation of injury when blood flow is restored
• Reactive oxygen species (ROS) and free radical generation
• Complement activation and neutrophil/platelet-endothelial interaction
• Cytokine release → local and systemic inflammatory response

Cellular cascade:

Key Toxic Substances Released

Pathogenesis of Renal Failure (Most serious complication)

1. Pre-renal AKI: Hypovolemia from fluid sequestration into crushed muscle (third-spacing) → reduced renal perfusion pressure
2. Intrinsic AKI - Tubular obstruction: Myoglobin and uric acid precipitate in distal tubules, especially in acidic urine (pH < 5.6)
3. Intrinsic AKI - Direct nephrotoxicity: Myoglobin forms ferrihemate, which generates hydroxyl radicals via Fenton reaction → oxidative tubular injury; acidic urine promotes dissociation of myoglobin into nephrotoxic ferriheme
4. Renal vasoconstriction: Activated renin-angiotensin system, hypovolemia, and inflammatory mediators reduce GFR
5. Macrophage extracellular traps: Recent research shows platelet-activated macrophages form METs that are pathogenic in rhabdomyolysis-induced AKI

Compartment Syndrome (local complication)

• Microvascular trauma → edema + interstitial bleeding within a closed fascial space
• Myocytes lose ability to retain intracellular water → further edema
• Rising pressure > 30 mmHg compresses microvasculature → muscle ischemia
• Irreversible nerve and muscle damage after 4-6 hours of ischemia

Full Pathophysiology Flowchart

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Signs and Symptoms

Local (Limb) Findings

• Swollen, tense, firm limb - due to edema and third-spacing of fluid
• Skin changes: ecchymosis, blistering, pressure necrosis, degloving injuries, lacerations
• Pain out of proportion to apparent injury (hallmark of developing compartment syndrome)
• Paresthesias: numbness, tingling, burning in the affected limb (nerve compression/ischemia)
• Weakness or paralysis of the compressed segment
• Pulselessness (late sign - major vessels often unaffected early; it is a microvasculature disorder)

The "5 Ps" of Compartment Syndrome

1. Pain (most consistent - out of proportion, worsened by passive stretch)
2. Paresthesias (earliest neurological sign)
3. Passive stretch pain (pain on passive movement of muscles in the compartment)
4. Pressure (palpably tense compartment)
5. Pulselessness (late and unreliable)

Systemic Findings

Classic Triad of Rhabdomyolysis

1. Myalgia (muscle pain and tenderness)
2. Generalized weakness
3. Dark (reddish-brown) urine

Note: In practice, only a minority of patients present with all three. Many present with only one or two components, requiring a high index of suspicion.

Timeline of complications

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Investigations

Bedside / Point-of-Care

• ECG: monitor for hyperkalemia changes (peaked T waves → widened QRS → sine wave → VF)
• Urinalysis (dipstick): positive for blood (myoglobin) but no RBCs on microscopy - this discrepancy is diagnostic
• Urine color: dark brown/tea-colored
• Compartment pressure measurement: Stryker device or saline manometer; >30 mmHg is diagnostic

Blood Tests

Serum CK <20,000 U/L carries lower AKI risk. CK as low as 5000 U/L can cause AKI if sepsis, acidosis, or volume depletion co-exist. - Comprehensive Clinical Nephrology, 7th Ed.

Urine Tests

• Urine myoglobin: confirms rhabdomyolysis (though clears faster than CK)
• Urine microscopy: pigmented granular casts (characteristic), absence of RBCs
• Urine pH: aim >6.5 with alkalization therapy
• Urine electrolytes and creatinine: for clearance calculations
• 24-hour urine output: monitoring for oliguria/polyuria during recovery

Imaging

• X-ray: fractures, pneumothorax (associated injuries)
• Ultrasound: compartment assessment, deep vein thrombosis (DVT)
• CT/MRI: defines extent of muscle necrosis; MRI is most sensitive for muscle damage
• ECG: continuous monitoring mandatory

Laboratory Follow-up Protocol

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Treatment

Pre-hospital / Field Management

• Begin IV fluid resuscitation before extrication if possible - this is the most effective intervention to prevent crush syndrome
• Use normal saline (0.9% NaCl) - avoid lactated Ringer's and other K+-containing fluids (risk of fatal hyperkalemia)
• Initial bolus: 1-2 L followed by 1000 mL/h, then reduce to 500 mL/h after 2 hours
• Continuous cardiac monitoring (ECG) - can be performed in confined spaces
• Immediate treatment of hyperkalemia: insulin + dextrose, calcium gluconate, beta-agonists, sodium bicarbonate, ion exchange resins

Fluid Resuscitation

• Target urine output: 200-300 mL/h (5-7 L/24 hours) for adults
• An average adult may require up to 12 L/day of fluids to sustain forced diuresis of 8 L/day
• Avoid fluid overload - monitor closely for pulmonary edema
• Urinary catheter placement is essential for monitoring

Alkaline Diuresis

• Once urine output is established: mannitol + sodium bicarbonate (alkaline diuresis)
• Maintain urine pH > 6.5 to prevent precipitation of myoglobin and uric acid in tubules
• Both myoglobin and uric acid are less nephrotoxic in alkaline urine
• Mannitol: osmotic diuretic, also reduces reperfusion injury component
• Target diuresis: up to 8 L/day

Management of Specific Complications

Fasciotomy (for Compartment Syndrome)

• Compartment pressure >30 mmHg (measured within 6 hours of injury)
• Delta pressure (diastolic BP - compartment pressure) <30 mmHg
• Absence of distal pulses
• Requirement for debridement of necrotic muscle

CRITICAL CAVEAT: Late fasciotomy (>12 hours post-entrapment, especially >12-24 hours) may cause massive myoglobin release from necrotic muscle, worsening renal failure. It also introduces infection risk into dead tissue. Most guidelines recommend against routine fasciotomy for late presentations of crush wounds, unless specific indications above are met. - Bailey & Love's Surgery, 28th Ed.

Hyperbaric Oxygen Therapy (HBO)

• Useful adjunct, particularly early post-injury
• At 2 atm: increases blood O2 content by 125%, increases tissue O2 tension 10-fold
• Reduces tissue edema via oxygen-induced vasoconstriction
• Long-term benefits: improved wound repair post-fasciotomy, reduced infection rates, better skin graft outcomes
• Does not replace fluid therapy

Dialysis

• Indications: refractory hyperkalemia, severe metabolic acidosis, fluid overload, oligoanuria with rising creatinine
• CRRT preferred in hemodynamically unstable patients
• Hemodialysis in stable patients
• Early dialysis (before overt uremia) may improve outcomes in disaster settings

Summary Treatment Algorithm

CRUSH INJURY IDENTIFIED
        ↓
Pre-extrication: IV NS 1-2L bolus → 1000 mL/h
ECG monitoring + treat hyperkalemia
        ↓
EXTRICATION
        ↓
Assess: Vitals, urine output, ECG, labs (CK, K+, Ca, pH, Cr)
Insert urinary catheter → target UO 200-300 mL/h
        ↓
UO established?
   YES → Add Mannitol + NaHCO3 (alkaline diuresis)
          Maintain urine pH > 6.5
   NO  → Increase fluid rate, reassess
        ↓
Compartment pressure >30 mmHg within 6 hrs? → Fasciotomy
        ↓
Renal failure? → Dialysis (HD or CRRT)
ARDS? → Mechanical ventilation
DIC? → FFP, platelets, cryoprecipitate
        ↓
ICU monitoring: serial labs q2-4h
K+, Ca, pH, Cr, CK, coagulation

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Complications

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Prognosis

• With early, aggressive fluid resuscitation before extrication, many patients survive without dialysis
• Without treatment, mortality from AKI is high
• Recovery of renal function is possible in many survivors if supported through the acute phase
• Long-term sequelae include chronic neuropathic pain (from scar tissue stretching sensitized nerve endings) - managed by desensitization therapy
• In mass casualty settings, limited dialysis availability is a major determinant of mortality

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Key Sources

• Rosen's Emergency Medicine: Concepts and Clinical Practice, 10th Ed. - "Crush Injury and Crush Syndrome"
• Tintinalli's Emergency Medicine: A Comprehensive Study Guide - "Crush Injury and the Crush Syndrome"
• Bailey and Love's Short Practice of Surgery, 28th Ed. - "Crush Injury and Syndrome"
• Comprehensive Clinical Nephrology, 7th Ed. - "Rhabdomyolysis"
• Recent meta-analysis (2026): Rostami P et al. BMC Emergency Medicine - "Crush injury syndrome in earthquakes: a systematic review and meta-analysis on its frequency and complications." [PMID: 41928063]