A 32-year-old man with a family history of sudden perioperative death is scheduled for elective knee arthroscopy under general anesthesia. Induction is performed with propofol and succinylcholine. Within 5 minutes of induction, the patient develops masseter muscle rigidity, followed by a rapid rise in end-tidal CO₂ (ETCO₂ from 35 to 65 mmHg in 10 minutes), core temperature rising from 37°C to 38.5°C, and dark-colored urine in the catheter. Heart rate is 140 bpm, blood pressure 160/95 mmHg. What is the most appropriate immediate management?

Explanation

## Recognition and Immediate Management of Malignant Hyperthermia **Key Point:** Malignant hyperthermia (MH) is a pharmacogenetic disorder triggered by exposure to succinylcholine and/or volatile anesthetics, characterized by uncontrolled muscle metabolism, rhabdomyolysis, and life-threatening hyperkalemia. ### Clinical Presentation in This Case The constellation of findings—masseter rigidity (earliest sign), rapidly rising ETCO₂ (most sensitive early indicator), hyperthermia, tachycardia, hypertension, and dark urine (myoglobinuria from rhabdomyolysis)—is pathognomonic for acute MH crisis. ### Immediate Management Protocol **High-Yield:** The STOP-DANT mnemonic encapsulates the emergency response: 1. **STOP** volatile anesthetics and succinylcholine immediately 2. **Hyperventilate** with 100% oxygen at increased minute ventilation (helps eliminate CO₂ and cool the body) 3. **Administer dantrolene sodium** 2.5 mg/kg IV bolus (can repeat every 5 minutes up to 10 mg/kg) - Dantrolene blocks calcium release from sarcoplasmic reticulum, halting the hypermetabolic cascade - Each 20 mg vial requires reconstitution with 60 mL sterile water (no bacteriostatic agents) 4. **Activate emergency protocols:** call for help, prepare ICU bed, notify lab for CK, myoglobin, potassium, coagulation studies 5. **Active cooling:** IV cold saline, surface cooling, ice to groin/axillae 6. **Treat hyperkalemia:** calcium gluconate, insulin + dextrose, sodium bicarbonate if peaked T waves or arrhythmias 7. **Monitor urine output:** maintain >200 mL/hr with aggressive hydration and furosemide to prevent acute kidney injury from myoglobinuria 8. **Observe for complications:** DIC, compartment syndrome, rhabdomyolysis-induced acute renal failure ### Why Dantrolene Is Essential **Clinical Pearl:** Dantrolene is the ONLY specific treatment for MH. It must be given early and in adequate doses; delay increases mortality and morbidity. Mortality has dropped from ~80% (pre-dantrolene era) to <5% with prompt recognition and treatment. ### Post-Crisis Management - Continue dantrolene 1 mg/kg IV every 4–6 hours for 24–48 hours to prevent recrudescence - Admit to ICU for continuous monitoring of temperature, potassium, CK, and urine myoglobin - Genetic counseling and testing (RYR1, CACNA1S mutations) for the patient and first-degree relatives - MH alert bracelet and avoidance of triggering agents in future anesthetics ```mermaid flowchart TD A[Induction with succinylcholine ± volatile]:::outcome --> B[Masseter rigidity + ↑ETCO₂ + ↑Temp]:::urgent B --> C{Suspect MH?}:::decision C -->|YES| D[STOP volatiles & succinylcholine]:::action D --> E[Hyperventilate 100% O₂]:::action E --> F[Dantrolene 2.5 mg/kg IV]:::action F --> G[Active cooling measures]:::action G --> H[Treat hyperkalemia]:::action H --> I[Aggressive IV hydration + furosemide]:::action I --> J[ICU admission, continue dantrolene 1 mg/kg Q4-6h]:::action J --> K[Genetic testing + counseling]:::outcome ``` **Warning:** Continuing volatile anesthesia or re-administering succinylcholine is catastrophic and will worsen the crisis. Ice-cold saline alone without dantrolene is insufficient—the underlying muscle hypermetabolism must be stopped pharmacologically.