What are typical triggers for malignant hyperthermia (MH) signs and initial steps when suspected intraoperatively?

• A. Slow rise in ETCO2, stable vitals; do not stop agents
• B. Hypothermia and bradycardia; stop agents, no further action
• C. Increase in blood pressure only; call for MH protocol
• D. Rapid rise in end-tidal CO2, muscle rigidity, tachycardia, hyperthermia; immediately stop triggering agents, call MH protocol, and administer dantrolene

Answer: (D)

Malignant hyperthermia is a rapid, life-threatening hypermetabolic crisis triggered by certain anesthetic agents, specifically volatile anesthetics and depolarizing muscle relaxants like succinylcholine. The earliest and most reliable intraoperative warning sign is a sharp rise in end-tidal CO2, reflecting the body’s sudden surge in metabolic heat and CO2 production. This progresses with signs such as muscle rigidity, especially in the jaw or chest, and tachycardia; if not addressed, hyperthermia follows and the crisis can escalate quickly.

The fastest, most effective initial response is to stop all triggering agents immediately and switch to 100% oxygen to maximize tissue oxygen delivery and remove residual anesthetic. Then activate the malignant hyperthermia protocol and administer dantrolene without delay. Dantrolene, started at about 2.5 mg/kg IV and repeated as needed, directly counteracts the abnormal calcium release in muscle that drives the crisis. Alongside this, provide aggressive cooling, monitor and correct acid–base and electrolyte disturbances (notably watch for hyperkalemia), ensure large-bore IV access and fluids, and prepare for ongoing management of the systemic effects and potential organ injury.

Other scenarios might show limited or slower changes and do not capture the characteristic combination of a rapid EtCO2 rise with rigidity and tachycardia, underscoring why stopping triggers and giving dantrolene promptly is essential.