A 32-year-old male presents for elective open reduction and internal fixation of a tibial fracture. Induction is uneventful with propofol and succinylcholine. Within 5 minutes of intubation and initiation of sevoflurane, the anesthesiologist notices the patient's end-tidal CO₂ (ETCO₂) has risen from 38 mmHg to 65 mmHg. The patient's core temperature is 37.8°C, muscle tone is markedly increased, and urine output is dark. Arterial blood gas shows pH 7.18, PaCO₂ 72 mmHg, and K⁺ 6.8 mEq/L. What is the most appropriate immediate management?

Explanation

## Diagnosis: Malignant Hyperthermia (MH) Crisis ### Clinical Recognition **Key Point:** The constellation of early ETCO₂ elevation (hypermetabolism), muscle rigidity, hyperkalemia (K⁺ 6.8), and dark urine (myoglobinuria) in the first 10 minutes of volatile anesthetic + succinylcholine exposure is pathognomonic for MH. **High-Yield:** ETCO₂ elevation is the EARLIEST and most sensitive sign of MH—often precedes fever by 30–60 minutes. Temperature rise is a LATE sign. ### Pathophysiology MH is a pharmacogenetic disorder of skeletal muscle calcium regulation (mutations in RYR1 or CACNA1S genes). Volatile anesthetics and/or depolarizing agents trigger uncontrolled sarcoplasmic reticulum Ca²⁺ release → sustained muscle contraction → hypermetabolism, heat production, rhabdomyolysis, and life-threatening hyperkalemia. ### Immediate Management Algorithm ```mermaid flowchart TD A["Suspected MH: ↑ETCO₂, rigidity, dark urine"]:::outcome --> B["Stop volatile anesthetics & succinylcholine"]:::action B --> C["Switch to TIVA: propofol + opioid"]:::action C --> D["Hyperventilate 100% O₂"]:::action D --> E["Dantrolene 2.5 mg/kg IV bolus"]:::action E --> F{"Response?"}:::decision F -->|"Rigidity resolves, ETCO₂ ↓"| G["Repeat dantrolene q 5 min, max 10 mg/kg"]:::action F -->|"No improvement"| H["Continue dantrolene; aggressive cooling"]:::action G --> I["Active cooling: ice packs, cold IV fluids, iced saline irrigation"]:::action H --> I I --> J["Monitor: core temp, K⁺, CK, urine myoglobin, coagulation"]:::action J --> K["ICU admission; continued dantrolene 1 mg/kg q 4-6 hrs × 24-48 hrs"]:::outcome ``` ### Dantrolene Mechanism **Clinical Pearl:** Dantrolene inhibits Ca²⁺ release from the sarcoplasmic reticulum by blocking the ryanodine receptor (RYR1). It is the ONLY specific treatment for MH. ### Supportive Measures 1. **Aggressive cooling** (target core temp < 38.5°C): ice packs to groin, axillae, neck; cold IV fluids; iced saline gastric/bladder irrigation if available. 2. **Hyperkalemia management:** Calcium gluconate (cardiac membrane stabilization), insulin + dextrose, sodium bicarbonate—but these are ADJUNCTIVE; dantrolene is definitive. 3. **Rhabdomyolysis prevention:** Aggressive IV hydration (target urine output 200–300 mL/hr); maintain urine pH > 6.5 with sodium bicarbonate to prevent myoglobin precipitation in renal tubules. 4. **Coagulopathy monitoring:** DIC is common; check PT/PTT, fibrinogen, D-dimer. 5. **Continued dantrolene:** 1 mg/kg IV q 4–6 hours for 24–48 hours post-crisis to prevent recrudescence. **High-Yield:** Do NOT delay dantrolene administration while awaiting confirmatory tests. Clinical suspicion = indication to treat. **Mnemonic: DANTROLENE DOSING — "2.5 first, then 1 q4h"** - Initial bolus: 2.5 mg/kg IV (may repeat q 5 min up to 10 mg/kg total) - Maintenance (post-crisis): 1 mg/kg IV q 4–6 hours × 24–48 hours ### Why NOT the Other Options - **Option 1 (correct):** Only answer addressing immediate cessation of triggers and dantrolene. - **Option 2:** Continuing volatile anesthesia is contraindicated and will worsen the crisis. - **Option 3:** Treating hyperkalemia without stopping the trigger (volatile anesthetic) and without dantrolene allows the underlying process to continue unchecked. - **Option 4:** Dantrolene MUST be given immediately; delaying it to ICU transfer increases mortality risk.