Malignant hyperthermia
Formal Definition
Malignant hyperthermia (MH) — a life-threatening, genetically predisposed pharmacogenetic disorder triggered in susceptible individuals by exposure to volatile anesthetic gases (halothane, sevoflurane, isoflurane, desflurane) and depolarizing muscle relaxants (succinylcholine); inheritance is autosomal dominant with incomplete penetrance involving ryanodine receptor (RYR1) gene mutations causing uncontrolled calcium release from sarcoplasmic reticulum, sustained muscle contraction, hypermetabolism, hyperthermia (often severe, rapid onset), rhabdomyolysis, hyperkalemia, acidosis, and potential cardiac arrest; treatment requires immediate recognition, withdrawal of triggering agent, administration of dantrolene sodium, cooling, and supportive ICU care.
How It's Used on the Ward
"Malignant hyperthermia" or "MH crisis" — the rare but deadly complication of general anesthesia in genetically susceptible patients where volatile anesthetics or succinylcholine cause a runaway hypermetabolic state; the patient suddenly gets rigid, hot (rising temperature rapidly), tachycardic, and acidotic on the OR table; dantrolene is the specific antidote and must be given immediately; survival depends on rapid recognition.
Example
""17-year-old healthy patient undergoing elective knee arthroscopy under general anesthesia. 5 minutes into sevoflurane + succinylcholine induction: jaw rigidity noticed, end-tidal CO2 rises from 32 to 65, HR 145, T 38.4°C climbing rapidly. Anesthesia attending: 'This is malignant hyperthermia. Stop volatile, call for dantrolene, switch to clean anesthesia, cool the patient.' Dantrolene 2.5 mg/kg IV bolus given within 8 minutes; total dose 250 mg. Patient cooled with ice packs and cold IV fluids. ICU admission post-op with continued dantrolene and supportive care. Survived; later RYR1 genetic testing confirmed MH susceptibility for family counseling.""
Clinical Context
Triggering agents: ALL volatile anesthetics (halothane, sevoflurane, isoflurane, desflurane) trigger MH; succinylcholine (depolarizing muscle relaxant) is the other major trigger; nitrous oxide, propofol, ketamine, all non-depolarizing muscle relaxants (rocuronium, vecuronium), opioids, benzodiazepines are SAFE. Safe technique for MH-susceptible patients: total intravenous anesthesia (TIVA) with propofol and remifentanil, no volatile, no succinylcholine, fully clean anesthesia machine. Initial MH signs (often earliest): elevated end-tidal CO2 (the most sensitive early sign), muscle rigidity (especially masseter spasm after succinylcholine), tachycardia, tachypnea/ventilation difficulty, hyperkalemia on ABG. Late signs: hyperthermia (often delayed and can be >40°C), rhabdomyolysis (CK elevation), myoglobinuria (dark urine), acidosis, ventricular arrhythmias. Treatment: (1) Stop volatile agent, (2) Dantrolene 2.5 mg/kg IV bolus, repeat q5min up to 10 mg/kg until symptoms resolve; (3) Increase ventilation with 100% O2; (4) External cooling (ice, cold fluids); (5) Treat electrolyte derangements (hyperkalemia, acidosis); (6) ICU monitoring for 24-72 hours; (7) Updated MH cart with dantrolene (or Ryanodex formulation) at every OR. MHAUS (Malignant Hyperthermia Association of the US) hotline for live consultation. Family testing is critical — MH is autosomal dominant.