Time-critical hypermetabolic crisis. Stop all triggers immediately, call for senior anaesthetic and ICU help, and start dantrolene early. Document times, doses and ABGs.
Suspect when
- During or soon after a volatile agent or suxamethonium
- Rising EtCO2 despite adequate ventilation (often the first sign)
- Tachycardia or arrhythmia, masseter spasm or generalised rigidity
- Hyperthermia (may be late), mixed metabolic and respiratory acidosis, rising CK, K+ and lactate
Triggers to stop
- All volatile agents (sevoflurane, desflurane, isoflurane)
- Suxamethonium
- Nitrous oxide alone is not a trigger; TIVA (propofol and opioid) is safe for maintenance
- Turn the vaporiser off, high fresh gas flow; do not delay dantrolene to change the circuit
Early suspicion
- Rising EtCO2, tachycardia
- Masseter spasm after suxamethonium
- Stop triggers, call for help
Established crisis
- Hyperthermia, rigidity, acidosis
- Dantrolene 2.5 mg/kg IV, repeat
- Active cooling, high fresh gas flow
Life-threatening
- Hyperkalaemic arrhythmia or arrest
- Treat K+, continue dantrolene
- ICU; recrudescence 24 to 48 h
Emergency pathway (in order)
1
1. Stop and ventilate
Stop all triggers. 100% oxygen and hyperventilate to clear CO2 (high minute volume). Declare an emergency, call for help, and abandon or finish surgery as safe.
Stop all triggers. 100% oxygen and hyperventilate to clear CO2 (high minute volume). Declare an emergency, call for help, and abandon or finish surgery as safe.
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2
2. Dantrolene
Dantrolene 2.5 mg/kg IV rapidly, repeated every 5 min until control (falling EtCO2, heart rate, temperature, rigidity). May exceed 10 mg/kg. Reconstitution is slow: assign several people to mix it.
Dantrolene 2.5 mg/kg IV rapidly, repeated every 5 min until control (falling EtCO2, heart rate, temperature, rigidity). May exceed 10 mg/kg. Reconstitution is slow: assign several people to mix it.
↓
3
3. Cool and support
Active cooling if hyperthermic (cold IV fluids, ice packs to groin, axillae and neck); stop at 38.5 C to avoid overcooling. Treat hyperkalaemia and acidosis. Maintain urine output (myoglobinuria). Avoid calcium channel blockers with dantrolene.
Active cooling if hyperthermic (cold IV fluids, ice packs to groin, axillae and neck); stop at 38.5 C to avoid overcooling. Treat hyperkalaemia and acidosis. Maintain urine output (myoglobinuria). Avoid calcium channel blockers with dantrolene.
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4
4. Monitor
Core temperature, EtCO2, ABG, K+, CK, lactate, clotting and urine output. Admit to ICU. Recrudescence can occur for 24 to 48 h: keep dantrolene available.
Core temperature, EtCO2, ABG, K+, CK, lactate, clotting and urine output. Admit to ICU. Recrudescence can occur for 24 to 48 h: keep dantrolene available.
After stabilisation
- Contact the MH Association and refer the patient and family for testing
- Document the record, times, drugs and dantrolene batches
- Future anaesthesia must be trigger-free (TIVA); flag and wristband
Pitfalls
- Delaying dantrolene while changing the circuit
- Calcium channel blockers with dantrolene (hyperkalaemia, collapse)
- Overcooling
- Not warning about recrudescence over 24 to 48 h
MedPrep - www.medprep.uk - Educational revision aid only. Not clinical guidance. Doses are adult examples; check the BNF, current guidelines and local policy, and seek senior advice. Nov 2026