Crush Syndrome

Two diagnoses, one injury. A crush injury is the direct local tissue damage caused by sustained mechanical compression of a body part. Crush syndrome (traumatic rhabdomyolysis) is the systemic sequel: the rhabdomyolysis, electrolyte disturbance and acute kidney injury (AKI) that follow compression and, critically, the moment of reperfusion when the limb is released. The condition was first characterised by Bywaters and Beall during the London Blitz of 1941, who linked limb crush to dark urine and fatal renal failure.

Who gets it. Earthquakes and building collapse are the leading cause of mass-casualty crush. It also follows industrial and motor-vehicle entrapment, and prolonged immobilisation: the "long-lie" after collapse, overdose, or being found down. After major earthquakes a significant minority of rescued survivors develop crush-related AKI, and the proportion requiring dialysis depends heavily on rescue speed and access to renal services.

What raises the risk. Risk rises sharply with:

• Entrapment beyond roughly 4-6 hours
• Large muscle-mass involvement: thigh, trunk, bilateral limbs
• Delayed or absent pre-extrication resuscitation

Crush syndrome is the systemic expression of traumatic rhabdomyolysis. That page covers the non-traumatic causes and the biochemistry in more depth; what follows is specific to the compressed and then reperfused limb.

Compression. Direct pressure plus arterial occlusion produces myocyte ischaemia. ATP depletion disables the Na+/K+ and Ca2+ pumps, so sodium, water and calcium flood into the cells while potassium and myoglobin leak out. The venous outflow is occluded too, so while the limb is still compressed the muscle is relatively protected from acute systemic toxicity: the toxins are trapped.

Release. On extrication, restored blood flow flushes the accumulated potassium, myoglobin, phosphate, urate, lactate and creatine kinase into the systemic circulation. This sudden potassium and acid load can precipitate ventricular fibrillation within minutes, the classic "smiling death" or extrication death.

Fluid sequestration. Reperfused muscle sequesters massive volumes of fluid, litres per limb, causing profound hypovolaemia, hypotension and worsening renal hypoperfusion. Compartment pressures rise, perpetuating the ischaemia.

The kidney. AKI results from three converging mechanisms:

• Renal vasoconstriction: hypovolaemia plus scavenging of nitric oxide by myoglobin
• Intratubular cast formation: myoglobin precipitating with Tamm-Horsfall protein in acidic urine
• Direct myoglobin/ferrihaemate tubular toxicity with oxidative injury

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In the limb. A swollen, tense and often pulseless limb, with pain out of proportion and pain on passive stretch, sensory loss, paraesthesia and motor weakness, and skin that shows necrosis, blistering or fixed compression marks.

Systemically. After release the patient becomes hypovolaemic and shocked as fluid third-spaces into the muscle, passes dark tea- or cola-coloured urine from myoglobinuria, and is at risk of cardiac arrhythmia from hyperkalaemia. Oliguria progresses to anuria, and nausea, confusion and the features of metabolic acidosis complete the picture.

Laboratory investigations. The findings to expect, and what each one is for:

CK, not myoglobin. CK is the more reliable quantitative marker because serum myoglobin clears rapidly.

The ECG. Potassium writes its progress on the trace, and the sequence is worth knowing in order:

1. Early: tall, tented T waves and a short QT
2. Moderate: P-wave flattening and loss of P waves, PR prolongation, progressive QRS widening
3. Severe: the broad QRS merges with the T wave into a sine-wave pattern, heralding ventricular fibrillation or asystole

Priorities. Never extricate a long-entrapped limb without intravenous (or intraosseous) fluids running and a plan for hyperkalaemia, and treat hyperkalaemia and hypovolaemia before any orthopaedic intervention. In order:

1. Pre-extrication fluids, which prevent cardiac arrest at release
2. Treat hyperkalaemia, the immediate life threat
3. Massive intravenous fluid resuscitation, which prevents AKI
4. Continuous cardiac monitoring
5. Consider dialysis early if oliguria persists

Algorithm

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Who does badly. Early aggressive management significantly improves survival; the poor prognostic factors are:

• Entrapment greater than 6 hours
• Trunk or bilateral limb involvement
• A very high CK: a figure of 75,000 U/L is conventionally quoted, but we could not trace it to a primary source and it should be treated as a rule of thumb rather than a validated cut-off
• Delayed fluid resuscitation
• DIC
• Multi-organ failure

Do not prognosticate from the renal stage. When modified RIFLE criteria were applied to 416 Marmara crush victims, a worse category predicted more medical complications, more dialysis sessions and a lower discharge GFR, but did not discriminate survival at all. Renal severity tells you what resources the patient will consume; it does not tell you whether they will live.

What kills these patients is extra-renal: the Marmara series attributed death to sepsis, thrombocytopenia, DIC, ARDS and thoraco-abdominal trauma rather than to renal failure itself, and in a mass-casualty triage that matters, because the sickest kidney is not the same patient as the sickest victim.

Global Epidemiology

Crush syndrome arises in three broad contexts worldwide: natural disasters (earthquakes are the dominant cause of mass-casualty crush, e.g. Marmara 1999, Kashmir 2005, Haiti 2010, Turkey-Syria 2023), industrial and motor-vehicle entrapment (mining, construction, building collapse, prolonged extrication after road traffic collisions), and prolonged immobilisation (collapse with "long-lie", drug overdose, the elderly found-down). After a major earthquake, crush-related AKI develops in a substantial minority of rescued survivors; the proportion needing dialysis varies enormously with rescue speed and access to renal services - illustrated by the Marmara series (74.6% of renal victims dialysed) versus the rural Kashmir earthquake, where far fewer reached dialysis at all.

Side-by-Side Guidance

High- vs Limited-Resource Practice Variation

In well-resourced settings, rapid extrication, point-of-care potassium, continuous renal replacement therapy and intensive care allow aggressive support and comparatively low renal-cause mortality. In limited-resource or austere disaster settings, delayed rescue, scarce dialysis and limited transport drive higher rates of hyperkalaemic death and amputation; field priorities shift toward early fluids, empirical hyperkalaemia treatment, and triage of who can be transferred for renal replacement. International coordination (e.g. deploying mobile dialysis capacity after earthquakes) materially changes outcomes.

Tourniquet at extrication. A proximal tourniquet applied before releasing a long-entrapped, clearly non-salvageable (mangled) limb can blunt the lethal reperfusion washout of potassium and myoglobin, and is part of field-amputation decision-making in mass-casualty settings. It is selective and debated, not routine, and must not delay fluid resuscitation; for a salvageable limb the priority remains pre-extrication fluids rather than ischaemic tourniquet time.

See tourniquet use for safe pressures and duration, and damage control orthopaedics for how these decisions sit within the wider resuscitation of a polytrauma patient.

Amputation or limb salvage. For a non-viable, heavily contaminated or overwhelmingly toxic limb, early amputation can be life-saving by removing the source of ongoing potassium and myoglobin load and infection, and is sometimes the correct disaster decision over repeated debridement of dead muscle. The threshold is a clinical judgement balancing systemic toxicity against limb salvage.