A 32-year-old male patient is scheduled for emergency cesarean section under general anesthesia. He has a history of malignant hyperthermia (MH) in his father. During induction, the anesthesiologist avoids volatile anesthetics and uses propofol-nitrous oxide-opioid technique. After intubation, succinylcholine 1 mg/kg IV is administered for muscle relaxation. Within 2 minutes of drug administration, the patient develops masseter muscle rigidity, followed by a rapid rise in end-tidal CO₂ (ETCO₂ from 35 to 60 mmHg), core temperature begins to rise, and urine becomes dark brown. What is the most appropriate immediate management?

Explanation

## Recognition and Management of Malignant Hyperthermia Crisis ### Clinical Presentation The patient exhibits classic early signs of malignant hyperthermia (MH): - Masseter muscle rigidity (earliest sign) - Rapid rise in ETCO₂ (hypermetabolism) - Core temperature elevation - Dark brown urine (myoglobinuria from rhabdomyolysis) ### Immediate Management Protocol **Key Point:** MH is a pharmacogenetic emergency requiring immediate cessation of triggering agents and rapid dantrolene administration. 1. **Stop triggering agents immediately** — discontinue all volatile anesthetics and succinylcholine 2. **Hyperventilate with 100% O₂** — increases CO₂ elimination and improves oxygenation 3. **Administer dantrolene 2.5 mg/kg IV stat** — inhibits calcium release from sarcoplasmic reticulum, halting muscle contraction cascade 4. **Active cooling measures** — ice packs, cold IV fluids, cold peritoneal lavage if needed 5. **Monitor and treat complications** — hyperkalemia, acidosis, myoglobinuria, DIC ### Why Succinylcholine is Contraindicated in MH Succinylcholine is a **triggering agent** in genetically susceptible individuals. It causes sustained depolarization and uncontrolled calcium release, precipitating the MH crisis. Administering additional doses would worsen the condition catastrophically. **High-Yield:** The two classic MH triggers are: - **Depolarizing agents:** succinylcholine - **Volatile anesthetics:** all halogenated agents (sevoflurane, isoflurane, desflurane) ### Dantrolene Mechanism Dantrolene acts on the **ryanodine receptor (RyR1)** in skeletal muscle sarcoplasmic reticulum, blocking calcium release. This interrupts the excitation-contraction coupling cascade and terminates the MH crisis. ### Complications to Monitor | Complication | Mechanism | Management | |---|---|---| | Hyperkalemia | Muscle breakdown + depolarization | Calcium gluconate, insulin-glucose, hyperventilation | | Myoglobinuria | Rhabdomyolysis | Aggressive fluid resuscitation, maintain urine output >200 mL/hr | | Acidosis | Hypermetabolism + hypoxia | Hyperventilation, sodium bicarbonate if severe | | DIC | Tissue injury + thromboplastin release | FFP, platelets, cryoprecipitate as needed | **Clinical Pearl:** Masseter muscle rigidity (MMR) alone is not diagnostic of MH — it can occur with normal anesthesia — but when combined with other signs (ETCO₂ rise, temperature elevation, myoglobinuria) in the context of succinylcholine exposure, MH must be assumed until proven otherwise. **Warning:** Continuing surgery or switching to another muscle relaxant delays definitive treatment and allows the cascade to progress, increasing mortality and morbidity.