A 28-year-old male from rural Maharashtra is scheduled for elective open reduction and internal fixation of a fractured femur. Induction is performed with propofol and succinylcholine. Within 2 minutes of intubation, the anesthesiologist notices the jaw is rigid, the patient's temperature is rising (37.8°C), and the end-tidal CO₂ is 65 mmHg. Muscle rigidity is evident throughout the body. Arterial blood gas shows pH 7.18, PaCO₂ 78 mmHg, and K⁺ 6.2 mEq/L. What is the most appropriate immediate management?

Explanation

## Recognition and Immediate Management of Malignant Hyperthermia **Key Point:** Malignant hyperthermia (MH) is a pharmacogenetic crisis triggered by exposure to succinylcholine and/or volatile anesthetics. Early recognition and immediate cessation of triggering agents with dantrolene administration are life-saving. ### Clinical Presentation in This Case The triad of signs—masseter muscle rigidity (jaw stiffness), rapid rise in end-tidal CO₂ (hypermetabolism), and muscle rigidity—within minutes of succinylcholine exposure is pathognomonic for MH. **High-Yield:** Early signs include: - Masseter muscle rigidity (earliest and most sensitive) - Unexplained tachycardia - Rapid rise in ETCO₂ (often the first objective sign) - Muscle rigidity (generalized) - Myoglobinuria (later) - Rhabdomyolysis-induced hyperkalemia (K⁺ 6.2 mEq/L here) ### Immediate Management Protocol **High-Yield:** The acronym **STOP-MH** guides management: 1. **S** — **Stop** all triggering agents immediately (succinylcholine, volatile anesthetics) 2. **T** — **Treat** with dantrolene sodium 2.5 mg/kg IV bolus; repeat every 5 minutes up to 10 mg/kg if signs persist 3. **O** — **Oxygenate** with 100% O₂ and hyperventilate to eliminate volatile anesthetic and reduce CO₂ 4. **P** — **Proceed** with surgery using non-triggering agents (propofol, opioids, non-depolarizing agents, nitrous oxide) **Clinical Pearl:** Dantrolene acts by blocking calcium release from the sarcoplasmic reticulum in skeletal muscle, halting the uncontrolled muscle metabolism and heat generation. ### Supportive Measures - Active cooling: ice packs, cold IV fluids, gastric/bladder lavage if core temperature >38.5°C - Treat hyperkalemia: calcium gluconate, insulin + glucose, sodium bicarbonate - Monitor urine output and maintain urine pH >6.5 with sodium bicarbonate to prevent myoglobin precipitation in renal tubules - Check CK, myoglobin, coagulation profile (DIC risk) **Mnemonic:** **DANTROLENE = DANTRium for Rhabdomyolysis and Elevated Temperature in Neuroleptic/anesthetic Emergency** ### Why This Case Fits MH - Succinylcholine exposure (known trigger) - Masseter rigidity (earliest sign) - Rapid ETCO₂ rise (hypermetabolism) - Acidosis + hyperkalemia (rhabdomyolysis) - Young male (MH more common in younger patients) **Warning:** Failure to recognize and treat MH within minutes leads to fulminant rhabdomyolysis, DIC, acute kidney injury, and death. This is a true anesthetic emergency.