A 32-year-old male patient is undergoing elective open cholecystectomy under general anesthesia with propofol induction and sevoflurane maintenance. Fifteen minutes into surgery, the anesthesiologist notices a sudden rise in end-tidal CO₂ (ETCO₂) from 38 to 52 mmHg, increased jaw rigidity, and a core temperature of 38.5°C. Heart rate is 128/min and blood pressure is 165/95 mmHg. What is the most appropriate immediate next step in management?

Explanation

## Recognition and Immediate Management of Malignant Hyperthermia ### Clinical Presentation The patient exhibits the classic early signs of malignant hyperthermia (MH): - **Elevated ETCO₂** (hypermetabolism — earliest and most sensitive sign) - **Muscle rigidity** (jaw clenching, masseter spasm) - **Tachycardia and hypertension** (sympathetic response) - **Rising core temperature** (late sign, not required for diagnosis) **Key Point:** MH is a pharmacogenetic crisis triggered by exposure to succinylcholine and/or volatile anesthetics. Early recognition and immediate dantrolene administration are life-saving. ### Why Dantrolene Is the Correct Answer **High-Yield:** Dantrolene sodium is the **only specific treatment** for malignant hyperthermia. It works by blocking calcium release from the sarcoplasmic reticulum in skeletal muscle, halting the hypermetabolic cascade. **Dosing and Administration:** - **Initial bolus:** 2.5 mg/kg IV push - **Repeat every 5 minutes** if signs persist (up to 10 mg/kg total) - Each vial (20 mg) must be reconstituted with 60 mL sterile water (no bacteriostatic agents) ### Immediate Management Algorithm ```mermaid flowchart TD A[Suspected MH: ↑ETCO₂, muscle rigidity, tachycardia]:::outcome A --> B[Stop volatile anesthetic immediately]:::action B --> C[Discontinue succinylcholine if used]:::action C --> D[Administer dantrolene 2.5 mg/kg IV]:::urgent D --> E[Hyperventilate with 100% O₂]:::action E --> F[Active cooling measures]:::action F --> G[Monitor core temperature, K⁺, CK, myoglobin]:::action G --> H{Persistent signs?}:::decision H -->|Yes| I[Repeat dantrolene q5min up to 10 mg/kg]:::urgent H -->|No| J[Complete surgery if stable, or abort]:::action J --> K[ICU admission for 24-48 hrs monitoring]:::action ``` ### Concurrent Supportive Measures 1. **Stop all triggering agents** — volatile anesthetics and succinylcholine 2. **Hyperventilate** with 100% O₂ to reduce ETCO₂ 3. **Active cooling** — ice packs, cold IV fluids, cold peritoneal/bladder irrigation 4. **Monitor and treat complications:** - Hyperkalemia (peaked T waves, dysrhythmias) → calcium gluconate, insulin + dextrose, sodium bicarbonate - Myoglobinuria → aggressive hydration, urine alkalinization, monitor urine color - Disseminated intravascular coagulation (DIC) → monitor PT/INR, fibrinogen **Clinical Pearl:** The rise in ETCO₂ is the **earliest and most reliable sign** of MH — it precedes fever by 20–30 minutes. Do not wait for temperature elevation to initiate dantrolene. **Warning:** ~~Increasing minute ventilation alone~~ will not stop the underlying hypermetabolic process; dantrolene must be given immediately. ### Post-Crisis Management - Continue dantrolene 1 mg/kg IV every 4–6 hours for 24–48 hours - Admit to ICU for continuous monitoring (dysrhythmias, renal failure, DIC) - Arrange MH susceptibility testing (caffeine halothane contracture test or genetic testing) for the patient and first-degree relatives - Provide MH alert card and Medic-Alert bracelet [cite:Miller's Anesthesia 8e Ch 30]