Correct Answer: C. Suxamethonium
The clinical presentation of acute hyperthermia with muscle rigidity during anesthesia is pathognomonic for malignant hyperthermia (MH), a pharmacogenetic crisis triggered by exposure to halogenated volatile anesthetics (like halothane) and/or depolarizing neuromuscular blockers. Suxamethonium (succinylcholine) is a depolarizing agent that causes sustained depolarization of the muscle membrane, triggering uncontrolled calcium release from the sarcoplasmic reticulum in genetically susceptible individuals. This leads to sustained muscle contraction, hypermetabolism, rhabdomyolysis, and life-threatening hyperthermia. The combination of halothane (a known MH trigger) with suxamethonium dramatically increases the risk. Early signs include muscle rigidity, jaw clenching, increased end-tidal CO₂, tachycardia, and rapidly rising core temperature. Suxamethonium is the only depolarizing agent among the options and is the classic MH trigger when combined with volatile anesthetics. Non-depolarizing agents (curare, rocuronium, cis-atracurium) do not trigger MH. Management requires immediate cessation of triggering agents, hyperventilation with 100% oxygen, and IV dantrolene sodium (2.5 mg/kg bolus, repeated every 5 minutes up to 10 mg/kg), which blocks calcium release from the sarcoplasmic reticulum.
Why the other options are wrong
A. D-curare — D-curare is a non-depolarizing neuromuscular blocker that does not trigger malignant hyperthermia. It causes competitive antagonism at the acetylcholine receptor without causing sustained depolarization. Non-depolarizing agents are actually safer alternatives in MH-susceptible patients. The NBE trap here is listing a neuromuscular blocker that students might confuse with suxamethonium if they don't recall the specific MH-triggering mechanism. B. Rocuronium — Rocuronium is a modern non-depolarizing neuromuscular blocker with rapid onset, commonly used in Indian operating theaters as a suxamethonium alternative. It does not trigger malignant hyperthermia because it acts competitively at the acetylcholine receptor without causing sustained depolarization or abnormal calcium handling. This option tests whether students confuse all neuromuscular blockers as MH triggers. D. Cis-atracurium — Cis-atracurium is a non-depolarizing agent that undergoes Hofmann elimination and ester hydrolysis, making it useful in renal/hepatic failure. It does not trigger malignant hyperthermia. The NBE trap is pairing it with halothane to test whether students know that only depolarizing agents (suxamethonium) combined with volatile anesthetics cause MH, not non-depolarizing agents.
High-Yield Facts
- Malignant hyperthermia is triggered by halogenated volatile anesthetics (halothane, isoflurane, sevoflurane) and suxamethonium (depolarizing agent only).
- Suxamethonium causes sustained depolarization → uncontrolled sarcoplasmic reticulum calcium release → sustained muscle contraction and hypermetabolism.
- Early MH signs: muscle rigidity, jaw clenching, increased end-tidal CO₂, tachycardia; late sign is hyperthermia (core temperature rises 1–2°C per minute).
- Dantrolene sodium (2.5 mg/kg IV, repeat every 5 min up to 10 mg/kg) is the only specific treatment; blocks ryanodine receptor calcium release.
- Non-depolarizing agents (rocuronium, cis-atracurium, vecuronium) do NOT trigger MH and are safe alternatives in susceptible patients.
- MH is inherited as autosomal dominant with variable penetrance; mutations in RYR1 (ryanodine receptor) or CACNA1S genes.
Mnemonics
MH Triggers: HAVOC Halothane, Anesthetics (volatile), Vapor, Other volatiles (isoflurane, sevoflurane), Choline (suxamethonium/depolarizing agents). Use this to recall that only depolarizing agents + volatile anesthetics cause MH. Early MH Signs: CHOP CO₂ (↑ end-tidal), Hyperthermia (late), Opening (jaw clenching/trismus), Pulse (tachycardia). Helps identify MH before core temperature rises dangerously.
NBE Trap
NBE pairs halothane (a known volatile trigger) with multiple neuromuscular blockers to test whether students know that only suxamethonium (depolarizing) triggers MH, not non-depolarizing agents. Students who confuse all neuromuscular blockers as MH triggers will be trapped into choosing rocuronium or cis-atracurium.
Clinical Pearl
In Indian operating theaters, suxamethonium is still widely used for rapid sequence intubation despite MH risk. Anesthesiologists must maintain a high index of suspicion when halothane + suxamethonium is used, especially in families with unexplained perioperative deaths. Dantrolene must be immediately available in all ORs; delayed administration increases mortality from rhabdomyolysis and acute kidney injury.
_Reference: KD Tripathi Ch. 12 (Neuromuscular Blocking Agents); Harrison Ch. 470 (Anesthetic Complications)_