Malignant hyperthermia
Stem
A 19-year-old man, 78 kg, is having an open reduction and internal fixation of a tibial fracture under general anesthesia with sevoflurane after a rapid sequence induction with succinylcholine. Forty minutes into the case, end-tidal CO2 has climbed from 38 to 62 mmHg despite doubling the minute ventilation. Heart rate is 128, the jaw and limbs are stiff, and his temperature is 38.1 °C and rising.
Question
What is happening, and how will you manage it?
Ideal answer
HeadlineMalignant hyperthermia until proven otherwise: CO2 outpacing my ventilation, tachycardia and rigidity after two triggers. I call for help and the MH cart.
- Trigger off. Sevoflurane and vaporizer out, propofol so surgery can finish or abort fast; 100% oxygen at 10 L/min fresh gas flow, hyperventilating.
- Dantrolene 2.5 mg/kg IV rapidly, about 200 mg, repeated until CO2, rigidity and heart rate fall; past 10 mg/kg without response, I rethink the diagnosis.1 One person only mixes.
- Treat the consequences. Bicarbonate for acidosis; calcium, insulin and dextrose for hyperkalemia; antiarrhythmics, never calcium-channel blockers; cooling that stops below 38 °C.1
- Measure. Arterial line; gas, potassium, CK, myoglobin, coagulation; urine output pushed to protect the kidneys.
- ICU on dantrolene for at least 24 hours, because it recurs.1
Breaking down the answer
- Name it first — shows judgment. Mimics: light anesthesia, hypoventilation or spent absorbent, sepsis, thyroid storm, pheochromocytoma, neuroleptic malignant and serotonin syndromes; CO2 that rises as I raise ventilation points to MH.
- Dantrolene before everything — the only specific treatment; it blocks calcium release from the sarcoplasmic reticulum, and the rest buys time. The 20 mg vials need 60 mL of sterile water each, hence a dedicated mixer.2
- Flush, do not rebuild — high flow clears volatile faster than swapping equipment; activated charcoal filters if on the cart.1
- Potassium kills — from rhabdomyolysis: calcium chloride 10 mg/kg (max 2 g), insulin 10 units with 50 mL of 50% dextrose in adults, bicarbonate 1–2 mEq/kg.1 Calcium-channel blockers plus dantrolene cause hyperkalemia and collapse; I use amiodarone, lidocaine or a beta-blocker.
- Cool, stop at 38 °C — after-drop hypothermia is real: external cooling, then 20 mL/kg chilled IV fluid, lavage of an already-open cavity only if needed.3
- Recrudescence — one in five, 80% of them within 16 hours, hence the maintenance dose in the table.4
Follow-up question
Twenty minutes later, after 5 mg/kg of dantrolene, the monitor shows wide-complex ventricular tachycardia with a pulse, and the potassium comes back at 7.2.
What do you do?
Follow-up answer
HeadlineHyperkalemic VT from ongoing muscle breakdown; I say so to the room.
Pulseless, ACLS; unstable with a pulse, synchronized cardioversion. Then the potassium: calcium chloride for the membrane, insulin, dextrose and bicarbonate to shift it, continued hyperventilation.1 More dantrolene, because potassium will not settle while muscle releases it; no calcium-channel blockers. Potassium and gas every 10–15 minutes, watching the QRS narrow; nephrology early if oliguric, as dialysis may be needed.
Pitfalls that cost points
- Cooling or bicarbonate before dantrolene, or one dose not repeated to effect.
- A triggering anesthetic left running, or no ICU plan.
- Calling isolated masseter spasm MH: stop elective surgery and monitor, no reflexive dantrolene.
Rapid-fire
Q: Why does end-tidal CO2 rise before temperature? A: Uncontrolled calcium release drives metabolism, so CO2 climbs at once; heat accumulates slowly.
Q: Which drugs are safe in a susceptible patient? A: Propofol, opioids, benzodiazepines, ketamine, etomidate, nitrous oxide, local anesthetics and all non-depolarizing relaxants.
Q: How do you prepare a machine for a known-susceptible patient? A: Vaporizers out, new absorbent and circuit, high-flow flush for the manufacturer's time (10 to over 90 minutes), or activated charcoal filters after a 90-second flush.5
Q: Which myopathies are linked to MH? A: Central core, multiminicore and King-Denborough; Duchenne and Becker are not MH-susceptible but risk hyperkalemic rhabdomyolysis with succinylcholine.
Q: What do you tell the family afterward? A: It is inherited: first-degree relatives are susceptible until contracture or RYR1 genetic testing; he needs a medical alert and a letter for future anesthetics.
Numbers to know
| Item | Value |
|---|---|
| Dantrolene initial | 2.5 mg/kg IV, repeat to effect1 |
| Dantrolene maintenance | 1 mg/kg every 4–6 h for ≥24 h4 |
| Vial reconstitution | 20 mg in 60 mL sterile water; 250 mg in 5 mL (Ryanodex)2 |
| Cooling endpoint | Stop below 38 °C3 |
| Recrudescence | ~20%, mostly within 16 h4 |
| Charcoal filters | Effective after a 90 s high-flow flush5 |
| MHAUS hotline | 1-800-644-97372 |
Links
- succinylcholine, Volatile agents and nitrous oxide: when and when not, hyperkalemia, Muscular dystrophies and myotonias, ACLS adapted to the operating room
- Atlas: Capnography: waveforms and sudden loss of ETCO2; Monitor atlas: other perioperative and peripartum events
- MHAUS treatment protocol (current version)
Sources
- 1.Managing a Crisis (MH treatment protocol) · MHAUS · mhaus.org
- 2.What should be on an MH cart? · MHAUS · mhaus.org
- 3.Evidence-based interventions to alleviate hyperthermia associated with MH · MHAUS · mhaus.org
- 4.Dantrolene Administration After an MH Event · MHAUS · mhaus.orgRecrudescence 20% of 308 patients (Burkman, Anesthesiology 2007).
- 5.Preparation of Anesthesia Workstations to Anesthetize MH-Susceptible Patients · MHAUS · mhaus.org
Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.