A 35-year-old male with no significant past medical history undergoes elective knee arthroscopy under general anesthesia with propofol induction and sevoflurane maintenance. Intraoperatively, the patient develops unexplained tachycardia (HR 145/min), hypertension (BP 180/110 mmHg), muscle rigidity, and a core temperature of 39.2°C. Arterial blood gas shows pH 7.28, pCO₂ 58 mmHg, pO₂ 95 mmHg, and serum potassium 6.8 mEq/L. Which of the following is the MOST appropriate immediate management?

Explanation

## Malignant Hyperthermia (MH) Diagnosis and Management The clinical presentation is pathognomonic for **malignant hyperthermia**: - Unexplained intraoperative tachycardia and hypertension - Muscle rigidity (masseter muscle rigidity or generalized) - Rapid rise in core temperature (39.2°C) - Respiratory acidosis (pCO₂ 58) with metabolic component - Hyperkalemia (6.8 mEq/L) from muscle breakdown ### **Key Point: Immediate Management Protocol** **STOP all triggering agents immediately:** - Discontinue volatile anesthetics (sevoflurane, desflurane, isoflurane) - Discontinue succinylcholine if used - Switch to safe agents (TIVA with propofol, non-depolarizing neuromuscular blockers, opioids, nitrous oxide is safe) **Dantrolene sodium administration:** - **Initial dose: 2.5 mg/kg IV rapid bolus** - Repeat every 5 minutes up to maximum 10 mg/kg until signs of MH resolve - Dantrolene inhibits calcium release from sarcoplasmic reticulum, preventing sustained muscle contraction - This is the ONLY specific treatment for MH **Supportive measures:** - Hyperventilate with 100% O₂ to treat respiratory acidosis and increase elimination of volatile anesthetic - Active cooling: ice packs to groin, axillae; cold IV fluids; cold peritoneal lavage if available - Treat hyperkalemia: calcium gluconate (cardiac membrane stabilization), insulin + dextrose, sodium bicarbonate - Monitor urine output and color (myoglobinuria risk); maintain urine output >200 mL/hr with fluids and furosemide - Continue dantrolene 1 mg/kg IV every 4–6 hours for 24–48 hours post-event ### **Clinical Pearl:** Malignant hyperthermia is a pharmacogenetic disorder of skeletal muscle calcium regulation. Early recognition and dantrolene administration are life-saving. Temperature rise is a LATE sign; do not wait for fever to diagnose MH.