A 35-year-old male patient is undergoing elective laparoscopic cholecystectomy under general anesthesia. After induction with propofol and intubation with succinylcholine, the anesthesiologist begins maintenance with isoflurane at 1.2% end-tidal concentration. Intraoperatively, the patient develops unexplained tachycardia (HR 140/min), muscle rigidity, and a core temperature rise to 38.5°C. The end-tidal CO₂ has risen to 65 mmHg. What is the most appropriate immediate next step?

Explanation

## Clinical Scenario Recognition The constellation of signs — tachycardia, muscle rigidity, rising core temperature, and elevated end-tidal CO₂ — is pathognomonic for **malignant hyperthermia (MH)**. The use of succinylcholine (a known MH trigger) combined with isoflurane (a volatile agent that is also a potent MH trigger) in a susceptible patient has precipitated a fulminant crisis. ## Immediate Management Priority **Key Point:** The FIRST and MOST CRITICAL step in suspected MH is to **STOP all triggering agents immediately** — discontinue the volatile anesthetic and succinylcholine at once. **High-Yield:** The mnemonic **STOP-MH** captures the sequence: - **S**top triggering agents (volatile + succinylcholine) - **T**ransition to safe anesthesia (IV propofol, opioids, benzodiazepines) - **O**xygenate aggressively (100% O₂, hyperventilate) - **P**repare dantrolene (but AFTER stopping triggers) ## Why Option 0 Is Correct 1. **Discontinue isoflurane** — removes the primary ongoing trigger 2. **Switch to IV propofol** — safe anesthetic with no MH association 3. **Hyperventilate with 100% O₂** — reduces end-tidal CO₂, cools the patient, and maximizes oxygenation Dantrolene is administered AFTER these immediate steps are secured, not as the first action. ## Dantrolene Timing **Clinical Pearl:** Dantrolene sodium (a ryanodine receptor antagonist) is the definitive treatment for MH, but it requires preparation time (mixing, IV access). The anesthesiologist must first eliminate the trigger and stabilize the patient's airway and oxygenation, then administer dantrolene 2.5 mg/kg IV push, repeated every 5 minutes up to 10 mg/kg if signs persist. ## Pathophysiology Context In MH-susceptible individuals, volatile anesthetics and succinylcholine cause uncontrolled calcium release from the sarcoplasmic reticulum, leading to sustained muscle contraction, heat generation, and hypermetabolism (reflected in elevated CO₂). Stopping the trigger halts new calcium release; dantrolene blocks existing calcium release.