What are the earliest signs of malignant hyperthermia and the initial treatment?

• A. Sudden rise in end-tidal CO2 with tachycardia and muscle rigidity; stop triggering agents, administer dantrolene IV, and support cooling and ventilation.
• B. Hypotension and bradycardia; administer epinephrine and fluids.
• C. Decreased ETCO2; administer bicarbonate.
• D. Facial flushing and hives; administer antihistamines.

Answer: (A)

Malignant hyperthermia is an acute, life-threatening reaction to certain anesthetics that causes a sudden surge of calcium release in skeletal muscle, leading to a rapid rise in metabolic rate. The earliest clue is a sharp increase in end-tidal CO2, often accompanied by tachycardia and noticeable muscle rigidity. This combination signals that the body is entering a hypermetabolic crisis and CO2 production is skyrocketing despite ventilation attempts.

The best initial action is to stop any triggering agents immediately, then administer dantrolene IV. Dantrolene directly interrupts calcium release from the sarcoplasmic reticulum in muscle, which halts the hypermetabolic process. Alongside that, provide aggressive cooling and continued ventilatory support, and manage fluids and electrolytes to prevent complications like hyperkalemia and acidosis.

Other options describe problems or signs that aren’t typical of the early MH picture—hypotension and bradycardia aren’t the hallmark early signs; a decrease in end-tidal CO2 isn’t correct for MH, and bicarbonate or antihistamines address different conditions like hypotension from other causes or allergic reactions.