## Correct Answer: B. Dantrolene The clinical presentation of post-operative muscle rigidity following sevoflurane and succinylcholine administration is **malignant hyperthermia (MH)** until proven otherwise. Malignant hyperthermia is a pharmacogenetic disorder of skeletal muscle calcium regulation triggered by exposure to volatile anesthetics (sevoflurane, isoflurane, desflurane) and/or depolarizing neuromuscular blockers (succinylcholine). The pathophysiology involves uncontrolled calcium release from the sarcoplasmic reticulum, leading to sustained muscle contraction, rhabdomyolysis, hyperkalemia, and potentially fatal complications. **Dantrolene sodium** is the specific and only effective treatment for acute malignant hyperthermia. It acts as a ryanodine receptor antagonist, directly inhibiting calcium release from the sarcoplasmic reticulum and terminating the hypermetabolic crisis. The dose is 2.5 mg/kg IV bolus, repeated every 5 minutes up to a maximum of 10 mg/kg until signs of MH resolve (muscle rigidity decreases, temperature stabilizes, end-tidal CO₂ normalizes). Dantrolene must be reconstituted immediately as it has poor stability; each 20 mg vial requires 60 mL sterile water without bacteriostatic agents. In the Indian context, MH is rare but must be recognized early in operating theaters. Post-operative muscle rigidity is the hallmark sign. Dantrolene is the gold standard and should be available in all operating rooms performing general anesthesia. No other drug addresses the underlying pathophysiology of MH. ## Why the other options are wrong **A. Diazepam** — Diazepam is a benzodiazepine that provides muscle relaxation through CNS-mediated mechanisms and is useful for post-operative anxiety or mild muscle spasm, but it does NOT address the underlying sarcoplasmic reticulum calcium dysregulation in malignant hyperthermia. It will not terminate the hypermetabolic crisis or prevent rhabdomyolysis and is therefore ineffective in acute MH. **C. Paracetamol** — Paracetamol is an analgesic and antipyretic with no direct effect on skeletal muscle calcium handling or the pathophysiology of malignant hyperthermia. While it may be used post-operatively for pain control, it has no role in treating acute MH-induced muscle rigidity and will delay critical intervention. **D. Propranolol** — Propranolol is a beta-blocker used for tachycardia and hypertension management, which may occur secondary to MH, but it does not treat the primary muscle pathology. It addresses sympathetic manifestations only and will not reverse the calcium-mediated muscle rigidity or prevent rhabdomyolysis complications. ## High-Yield Facts - **Malignant hyperthermia triggers**: volatile anesthetics (sevoflurane, isoflurane, desflurane) + depolarizing blockers (succinylcholine); succinylcholine alone can trigger MH in susceptible individuals. - **Dantrolene mechanism**: ryanodine receptor antagonist → blocks sarcoplasmic reticulum calcium release → terminates hypermetabolic crisis. - **Dantrolene dosing**: 2.5 mg/kg IV bolus, repeat every 5 min up to 10 mg/kg total; reconstitute immediately with 60 mL sterile water (no bacteriostatic agents). - **Early signs of MH**: muscle rigidity, masseter jaw rigidity, increased end-tidal CO₂, tachycardia, hyperthermia (late sign); post-operative presentation is muscle rigidity. - **Post-MH management**: aggressive cooling, hyperventilation with 100% O₂, treat hyperkalemia (calcium gluconate, insulin-glucose), monitor for rhabdomyolysis and acute kidney injury. - **Succinylcholine contraindication**: absolute contraindication in known/suspected MH; use non-depolarizing agents (vecuronium, rocuronium) instead in susceptible patients. ## Mnemonics **MH Triggers: SAVAGES** **S**evoflurane, **A**ttracurium, **V**olatile agents, **A**nesthetics, **G**as anesthesia, **E**ther, **S**uccinylcholine. (Note: Attracurium is safe; the mnemonic emphasizes volatile anesthetics and succinylcholine as true triggers.) **Dantrolene Action: RYR Block** **RYR** = Ryanodine Receptor. Dantrolene blocks RYR on sarcoplasmic reticulum → stops calcium leak → muscle relaxation. Use when you see acute muscle rigidity post-anesthesia. ## NBE Trap NBE may pair benzodiazepines (diazepam) with muscle rigidity to trap students who confuse post-operative muscle spasm with malignant hyperthermia; diazepam is indeed used for spasm but NOT for MH. The key discriminator is the acute, severe, life-threatening presentation with sevoflurane + succinylcholine exposure. ## Clinical Pearl In Indian operating theaters, malignant hyperthermia is rare but catastrophic when missed. Any patient with acute post-operative muscle rigidity, especially after volatile anesthetic + succinylcholine, must trigger immediate dantrolene administration while simultaneously stopping the triggering agents, hyperventilating with 100% O₂, and aggressive cooling. Delay in dantrolene administration increases mortality and morbidity from rhabdomyolysis and hyperkalemia-induced cardiac arrhythmias. _Reference: Harrison Ch. 387 (Anesthesia); KD Tripathi Ch. 11 (Neuromuscular Blocking Agents & Dantrolene)_
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