A 35-year-old woman from Delhi is undergoing elective total abdominal hysterectomy under general anesthesia. Induction is routine with thiopental and vecuronium. After 20 minutes of isoflurane anesthesia, the surgeon notices the surgical field muscles are unusually firm and difficult to retract. The anesthesiologist observes the patient's core temperature is 39.2°C, end-tidal CO₂ has risen from 38 to 52 mmHg over 10 minutes, and the patient is sweating profusely. Arterial blood gas shows: pH 7.20, PaCO₂ 56 mmHg, HCO₃⁻ 22 mEq/L, K⁺ 5.8 mEq/L, and myoglobin is detectable in the urine. Which of the following is the LEAST appropriate immediate intervention?

Explanation

## Malignant Hyperthermia: Avoiding Triggering Agents ### Clinical Scenario Analysis **Key Point:** This patient presents with fulminant malignant hyperthermia triggered by isoflurane (a volatile anesthetic). The clinical triad is evident: muscle rigidity, hyperthermia (39.2°C), and hypercarbia (ETCO₂ 52 mmHg). The presence of myoglobinuria indicates severe rhabdomyolysis. ### Why Succinylcholine Is Contraindicated in MH **High-Yield:** Succinylcholine is a DEPOLARIZING neuromuscular blocker and is one of the two primary triggers of malignant hyperthermia (the other being volatile anesthetics). Administering it during an active MH crisis would: 1. **Worsen muscle calcium dysregulation** — succinylcholine causes sustained depolarization, further opening ryanodine receptors and releasing more calcium 2. **Accelerate rhabdomyolysis** — increased muscle contraction leads to more myoglobin release and hyperkalemia 3. **Deepen acidosis and hyperkalemia** — both life-threatening in the context of MH 4. **Delay definitive treatment** — time spent administering succinylcholine is time lost for dantrolene administration and cooling **Warning:** Succinylcholine is NEVER indicated in MH, whether suspected or confirmed. It is one of the two absolute contraindications in anesthesia (the other being local anesthetic overdose in a patient with pseudocholinesterase deficiency). ### Correct Management Hierarchy ```mermaid flowchart TD A[Confirmed/Suspected MH during surgery]:::urgent --> B[STOP volatile anesthetics immediately]:::action B --> C[Switch to TIVA: Propofol + Opioid]:::action C --> D[Administer dantrolene 2.5 mg/kg IV]:::action D --> E[Repeat dantrolene q5min up to 10 mg/kg]:::action E --> F[Hyperventilate 100% O₂]:::action F --> G[Active cooling: cold IV fluids, ice packs, cold peritoneal/gastric lavage]:::action G --> H[Treat hyperkalemia: Ca²⁺, insulin + glucose, NaHCO₃]:::action H --> I[Aggressive hydration + furosemide]:::action I --> J[Avoid succinylcholine at all costs]:::urgent ``` ### Appropriate Interventions in This Case | Intervention | Rationale | Status | | --- | --- | --- | | **Dantrolene 2.5 mg/kg IV** | Blocks SR calcium release; only specific MH treatment | ✓ Correct | | **Discontinue isoflurane** | Remove volatile trigger immediately | ✓ Correct | | **Switch to TIVA (propofol + remifentanil)** | Both are safe in MH; maintain anesthesia without triggering agents | ✓ Correct | | **Hyperventilate with 100% O₂** | Reduces ETCO₂, increases oxygenation, aids CO₂ elimination | ✓ Correct | | **Active cooling** | Counteract hyperthermia; ice packs, cold fluids, cold peritoneal lavage | ✓ Correct | | **Succinylcholine** | DEPOLARIZING agent; potent MH trigger; worsens crisis | ✗ **CONTRAINDICATED** | ### Neuromuscular Blockade in MH **Clinical Pearl:** In MH-susceptible patients: - **Safe agents:** Non-depolarizing blockers (rocuronium, vecuronium, cisatracurium, atracurium) - **Unsafe agents:** Succinylcholine (depolarizing) - **Reversal:** Use sugammadex (preferred) or neostigmine + glycopyrrolate This patient received vecuronium at induction (safe) but the volatile anesthetic isoflurane triggered the crisis. ### Post-Crisis Monitoring **High-Yield:** After initial dantrolene bolus and stabilization: - Continue dantrolene 1 mg/kg IV every 4–6 hours for 24–48 hours (prevent recrudescence) - Monitor: ECG, ABG, K⁺, CK, myoglobin, urine output, renal function - Admit to ICU for continuous monitoring - Counsel family for malignant hyperthermia susceptibility testing [cite:Miller's Anesthesia 8e Ch 34; Stoelting's Pharmacology and Physiology in Anesthetic Practice 5e]