Crush Syndrome
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Direct answer
Rhabdomyolysis begins while the victim is still trapped: crush syndrome is the systemic fallout of prolonged muscle compression — myoglobin, potassium, phosphate and acid pouring out of reperfusing muscle — and its earliest killer is hyperkalaemia causing cardiac arrest within minutes of release. The single most exam-tested intervention is intravenous fluid started before extrication, because the ischaemic muscle has been quietly leaking into a compressed limb and reperfusion delivers the load to the circulation. Expect tea- or cola-coloured urine (myoglobinuria), a creatine kinase in the tens of thousands, rising urea and creatinine, and sudden fatal arrhythmias; treat with aggressive saline, cardiac monitoring, calcium and insulin–dextrose for hyperkalaemia, alkalinisation and mannitol protocols where used, and renal replacement therapy when indicated. Crush syndrome is the surgical face of earthquake and disaster medicine, from the classic Bywaters descriptions of the London Blitz to modern building-collapse rescues.
What you must remember
- Diagnosis of rhabdomyolysis: creatine kinase above roughly 5,000 units/L (levels above 10,000 carry higher renal risk), myoglobinuria (dark brown urine with few red cells on microscopy, dipstick "blood" positive without haematuria), hyperkalaemia, hyperphosphataemia, hypocalcaemia, metabolic acidosis, and rising urea and creatinine.
- Fluids before freeing the victim: isotonic saline at high rates (commonly 1–1.5 L per hour in adults during extrication), avoiding potassium-containing solutions — Ringer's lactate contains potassium and is traditionally avoided.
- Hyperkalaemia kills first: continuous ECG, calcium chloride or gluconate to stabilise the myocardium, insulin with dextrose, salbutamol, sodium bicarbonate, and urgent dialysis if refractory; remember the sudden release phenomenon at extrication.
- Forced alkaline diuresis (saline plus sodium bicarbonate targeting urine pH above about 6.5, with mannitol in some protocols) aims to prevent myoglobin precipitating in renal tubules; mannitol remains controversial.
- Do not correct hypocalcaemia routinely — it is largely a translocation phenomenon that settles as muscle recovers; treat only for symptoms or hyperkalaemic ECG changes.
- Renal replacement therapy indications: refractory hyperkalaemia, acidosis, fluid overload or anuria despite optimised resuscitation; needs rise sharply in disasters.
- Fasciotomy decisions are treacherous: crush injury carries high infection and bleeding risk, so operate for a clear compartment syndrome, weighing coagulopathy and the need for dead-muscle debridement.
- Disaster triage angle: victims trapped over about 4 hours, or with extensive compression, are at highest risk; field protocols tag them for immediate fluid therapy.
How to work through it
After a building collapse, a man is pinned across both thighs for six hours. While the rescue team shores up the concrete, the medical team establishes intravenous access and starts normal saline — before a single block is moved — because release without volume expansion is the classical "smiling death": the patient jokes with rescuers and arrests in the ambulance. On extrication, monitoring shows peaked T waves; calcium gluconate is given, followed by insulin–dextrose and salbutamol, with bicarbonate and dialysis on standby. Urine output is preserved above 100 mL/hour with continuing saline, and the urine is the colour of strong tea with a positive dipstick for blood but no red cells on microscopy — myoglobinuria, effectively confirming the diagnosis alongside a creatine kinase over 60,000. Over the next days the hazards rotate: acute kidney injury (early dialysis when indicated), disseminated intravascular coagulation from released tissue thromboplastins, compartment syndrome of the calves (operated only for clear signs, with bleeding risk corrected first), and later hypercalcaemia during recovery as the sequestered calcium returns. Survivors of the renal phase usually recover kidney function completely — worth stating in a viva, because it frames the entire effort as buying time.
Where students slip
The sequence error dominates: candidates describe extrication first and resuscitation after. The second is fluid choice — Ringer's lactate (potassium-containing) is the trap option in every stem. Third is hypocalcaemia: reflex correction with calcium gluconate for a laboratory number is wrong; calcium is reserved for hyperkalaemic ECG changes or symptomatic hypocalcaemia, because routine loading risks metastatic calcification in injured muscle. Fourth, the urine: candidates call it "haematuria" — the dipstick is positive for blood but microscopy shows no red cells, and that dissociation is precisely the diagnostic pearl examiners reward.
Frequently asked questions
Why must fluids start before extrication?
Because reperfusion of crushed muscle releases potassium, myoglobin and acids into the circulation at the moment of release; pre-emptive volume expansion and a dilute, alkalinised urine reduce the sudden hyperkalaemic arrest and renal injury.
What creatine kinase level defines significant rhabdomyolysis?
Levels above about 5,000 units/L indicate clinically significant muscle injury with a real risk of acute kidney injury; crush victims often present in the tens or hundreds of thousands.
Why does the urine dipstick show blood without red cells?
Because myoglobin cross-reacts with the orthotolidine reagent on the dipstick, producing a positive "blood" reading while microscopy shows no erythrocytes — the classic dissociation indicating myoglobinuria.
Should hypocalcaemia in crush syndrome be treated?
Not routinely: calcium shifts into damaged muscle and returns during recovery; treat only for hyperkalaemic ECG changes or symptomatic hypocalcaemia, to avoid worsening the recovery-phase hypercalcaemia.
When is dialysis required in crush syndrome?
For refractory hyperkalaemia, severe metabolic acidosis, fluid overload, or anuria despite aggressive resuscitation — anticipated early, because crush victims often need renal support for days to weeks before full recovery.