In the PACU, a patient develops hyperthermia (39.8°C), muscle rigidity, tachycardia, and masseter spasm 20 minutes after receiving succinylcholine for tracheal intubation followed by isoflurane maintenance. Malignant hyperthermia is suspected. The FIRST pharmacological intervention is:

• A Sodium bicarbonate to correct metabolic acidosis
• B Propranolol to control tachycardia and prevent arrhythmia
• C Cooling blanket and ice packs to achieve target temperature <38°C
• D Dantrolene sodium 2.5 mg/kg IV, repeated to a maximum of 10 mg/kg ✓

Explanation

Dantrolene sodium is the specific treatment for malignant hyperthermia; it is a muscle relaxant that inhibits calcium release from the sarcoplasmic reticulum by blocking ryanodine receptor 1 (RyR1), directly interrupting the hypermetabolic crisis. The dose is 2.5 mg/kg IV bolus, repeated every 5 minutes to a total of 10 mg/kg (or until symptoms resolve); ongoing infusion at 1 mg/kg every 6 hours is maintained for 24–48 hours to prevent recurrence. Dantrolene must be given FIRST, concurrently with triggering agent removal, active cooling, bicarbonate for acidosis, and glucose-insulin for hyperkalaemia.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.