A 32-year-old male patient is undergoing elective abdominal surgery under general anesthesia. After induction with propofol and fentanyl, succinylcholine 1.5 mg/kg IV is administered for rapid sequence intubation. Within 30 seconds of administration, the patient develops severe muscle rigidity, trismus, and a rapid rise in core body temperature. Arterial blood gas shows pH 7.28, PaCO₂ 58 mmHg, and K⁺ 6.8 mEq/L. What is the most appropriate immediate next step in management?

Explanation

## Clinical Diagnosis: Malignant Hyperthermia (MH) The constellation of signs — muscle rigidity, trismus, hyperthermia, hypercarbia, and acute hyperkalemia following succinylcholine — is pathognomonic for malignant hyperthermia, a pharmacogenetic crisis triggered by depolarising muscle relaxants and volatile anesthetics. ## Pathophysiology **Key Point:** Malignant hyperthermia is caused by uncontrolled calcium release from the sarcoplasmic reticulum due to mutations in the ryanodine receptor (RYR1) or CACNA1S genes. Succinylcholine triggers sustained depolarisation, leading to: 1. Sustained muscle contraction → rhabdomyolysis 2. Massive K⁺ efflux from muscle → life-threatening hyperkalemia 3. Uncoupling of oxidative phosphorylation → exponential heat generation 4. Metabolic and respiratory acidosis from hypercarbia and anaerobic metabolism ## Immediate Management Algorithm ```mermaid flowchart TD A[Suspected MH: Rigidity + Hyperthermia + Hyperkalemia post-Succinylcholine]:::urgent A --> B[STOP all triggering agents]:::action B --> C[Administer dantrolene 2.5 mg/kg IV STAT]:::action C --> D[Hyperventilate with 100% O₂]:::action D --> E[Active cooling measures]:::action E --> F[Treat hyperkalemia: Insulin + Glucose, CaCl₃, Sodium bicarbonate]:::action F --> G[Monitor for complications: Rhabdomyolysis, DIC, Acute kidney injury]:::outcome G --> H[Admit to ICU; arrange MH testing post-recovery]:::action ``` ## Why Dantrolene? **High-Yield:** Dantrolene sodium is the ONLY specific treatment for MH. It works by: - Blocking calcium release from the sarcoplasmic reticulum via RYR1 inhibition - Reducing muscle metabolism and heat generation - Halting the cascade within minutes if given early Dose: 2.5 mg/kg IV bolus; repeat every 5 minutes up to 10 mg/kg if signs persist. ## Concurrent Supportive Measures | Intervention | Rationale | | --- | --- | | **Hyperventilation with 100% O₂** | Correct hypercarbia (PaCO₂ 58), improve oxygenation, and prevent hypoxia | | **Active cooling** | Ice packs to groin, axillae; cold IV saline; cold peritoneal lavage if core temp >39°C | | **Treat hyperkalemia** | Insulin 10 U + 25 g dextrose IV; CaCl₃ 10 mg/kg for cardiac membrane stabilisation; NaHCO₃ 1–2 mEq/kg | | **Urine alkalinisation** | Sodium bicarbonate to prevent myoglobin precipitation in renal tubules | | **Monitor CK, myoglobin, coagulation** | Screen for rhabdomyolysis and DIC | **Clinical Pearl:** The K⁺ of 6.8 mEq/L is life-threatening and can cause cardiac dysrhythmias; however, it is a *consequence* of MH, not the primary problem. Treating the underlying MH (dantrolene) is the priority — hyperkalemia management is supportive. **Warning:** Continuing volatile anesthetics or administering succinylcholine again will worsen the crisis. Switch to TIVA (propofol + opioid) if surgery must continue after stabilisation. ## Post-Crisis Management - Admit to ICU for continuous monitoring (core temperature, CK, urine output, coagulation) - Arrange muscle biopsy (caffeine-halothane contracture test) or genetic testing (RYR1/CACNA1S) for MH susceptibility - Counsel patient and family; issue MH alert card - Avoid all triggering agents in future anesthetics