A 32-year-old male patient is scheduled for elective open reduction and internal fixation of a tibial fracture. Induction is performed with propofol and succinylcholine. Five minutes after intubation, the anesthesiologist notices the patient's end-tidal CO₂ (ETCO₂) has risen from 38 mmHg to 62 mmHg. The patient's core temperature is 38.5°C, jaw muscles are rigid, and the surgical field shows dark-colored muscle. Arterial blood gas reveals pH 7.18, PaCO₂ 68 mmHg, and K⁺ 6.8 mEq/L. What is the most appropriate immediate management?

Explanation

## Diagnosis: Malignant Hyperthermia Crisis **Key Point:** Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle calcium regulation triggered by exposure to succinylcholine and/or volatile anesthetics, presenting with a characteristic triad of hypermetabolism, muscle rigidity, and uncontrolled heat production. ### Clinical Recognition in This Case | Sign | Significance | |------|---------------| | Rapid ETCO₂ rise (38→62 mmHg) | Earliest and most sensitive sign of hypermetabolism | | Jaw rigidity post-succinylcholine | Generalized muscle contracture (not pseudocholinesterase deficiency) | | Core temperature 38.5°C | Late sign; hypothermia may occur initially | | Dark muscle in surgical field | Myoglobinuria from rhabdomyolysis | | Hyperkalemia (K⁺ 6.8) | From muscle breakdown and acidosis | | Metabolic acidosis (pH 7.18) | Lactic acidosis from anaerobic metabolism | ### Immediate Management Algorithm ```mermaid flowchart TD A[Suspected MH Crisis]:::urgent --> B[STOP all triggering agents]:::action B --> C[Hyperventilate 100% O₂]:::action C --> D[Administer dantrolene 2.5 mg/kg IV]:::action D --> E[Repeat dantrolene q5min up to 10 mg/kg]:::action A --> F[Active cooling measures]:::action F --> G[Ice packs, cold IV fluids, cold peritoneal lavage] A --> H[Treat hyperkalemia]:::action H --> I[Calcium gluconate, insulin + glucose, sodium bicarbonate] A --> J[Monitor for complications]:::action J --> K[Rhabdomyolysis, DIC, acute kidney injury] ``` **High-Yield:** Dantrolene is a ryanodine receptor antagonist that blocks calcium release from the sarcoplasmic reticulum. It is the ONLY specific treatment for MH and must be given immediately — each 5-minute delay increases mortality. **Clinical Pearl:** ETCO₂ elevation is the earliest warning sign, often preceding temperature rise by 10–20 minutes. A rise >50% above baseline in the first 10 minutes of anesthesia is highly suspicious for MH. **Mnemonic:** **CHOP** — **C**ease triggering agents, **H**yperventilate with O₂, **O**pen dantrolene (2.5 mg/kg), **P**repare for complications (hyperkalemia, rhabdo, DIC). ### Why Dantrolene? - Rapidly reverses the pathophysiology by blocking calcium-induced muscle contraction - Reduces mortality from ~80% (untreated) to <5% (treated promptly) - Each vial (20 mg) requires 3 mL sterile water for reconstitution; prepare multiple vials in advance - Continued dosing q5 min until signs resolve or maximum 10 mg/kg reached ### Post-Crisis Management 1. **Aggressive fluid resuscitation** (target urine output 200–300 mL/hr) to prevent acute kidney injury from myoglobin precipitation 2. **Urine alkalinization** with sodium bicarbonate to increase myoglobin solubility 3. **Monitor for DIC** (platelet count, fibrinogen, D-dimer) 4. **Avoid succinylcholine and volatile agents** in future anesthetics 5. **Refer patient and first-degree relatives for MH susceptibility testing** (caffeine halothane contracture test or genetic testing) [cite:Miller's Anesthesia 8e Ch 33] [cite:Harrison 21e Ch 396]