A 35-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. Five minutes post-intubation, the patient develops severe hyperkalemia (K⁺ 7.2 mEq/L), masseter muscle rigidity, and a core temperature of 38.5°C. The surgeon requests to proceed with surgery. What is the most appropriate immediate next step?

Explanation

## Clinical Scenario Analysis This patient is exhibiting the classic triad of **malignant hyperthermia (MH)**: masseter muscle rigidity, hyperkalemia, and elevated core temperature following succinylcholine administration. ## Pathophysiology of Malignant Hyperthermia **Key Point:** Malignant hyperthermia is a pharmacogenetic disorder of skeletal muscle calcium regulation triggered by depolarising agents (succinylcholine) and volatile anesthetics. Uncontrolled calcium release from the sarcoplasmic reticulum leads to sustained muscle contraction, rhabdomyolysis, and life-threatening complications. ## Immediate Management Protocol 1. **Abort the procedure immediately** — continued anesthetic exposure worsens the crisis 2. **Hyperventilate with 100% O₂** — addresses metabolic acidosis and hypercapnia from muscle metabolism 3. **Administer dantrolene sodium 2.5 mg/kg IV** — the ONLY specific treatment for MH - Mechanism: Blocks calcium release from sarcoplasmic reticulum via ryanodine receptor antagonism - Repeat doses every 5 minutes up to 10 mg/kg if signs persist - Prepare dantrolene in advance (20 mg vials, each requires 60 mL sterile water for reconstitution) 4. **Concurrent supportive measures:** - Active cooling (ice packs, cold IV fluids, cold peritoneal lavage if needed) - Treat hyperkalemia: calcium gluconate, insulin-dextrose, sodium bicarbonate - Maintain urine output >200 mL/hr (prevent myoglobinuric acute kidney injury) - Monitor for disseminated intravascular coagulation (DIC) - Continuous cardiac monitoring (peaked T waves, prolonged PR interval) ## High-Yield Mnemonic **CHOP MH** — **C**ore temp ↑, **H**yperkalemia, **O**pisthotonos/muscle rigidity, **P**ost-op complications (DIC, rhabdo) → **M**alignant **H**yperthermia ## Key Differentiators from Other Causes | Feature | Malignant Hyperthermia | Neuroleptic Malignant Syndrome | Thyroid Storm | |---------|------------------------|--------------------------------|---------------| | **Trigger** | Succinylcholine, volatiles | Antipsychotics | Iodine, stress, infection | | **Onset** | Minutes (intra-op) | Hours to days | Gradual (hours) | | **Muscle rigidity** | Generalized, severe | Generalized, "lead pipe" | Mild to moderate | | **Treatment** | Dantrolene | Dantrolene (also works) | Propranolol, PTU, cooling | | **CK elevation** | Massive (>10,000) | Marked (>1,000) | Mild to moderate | **Clinical Pearl:** Masseter muscle rigidity (inability to open mouth) after succinylcholine is a **red flag** for MH susceptibility, even without full-blown crisis. Some centers now consider it an indication to abort and administer dantrolene prophylactically. ## Post-Crisis Management - Admit to ICU for 24–48 hours of monitoring (recrudescence can occur) - Arrange MH susceptibility testing (caffeine halothane contracture test or genetic testing) - Counsel family members (autosomal dominant inheritance) - Provide MH alert bracelet and wallet card [cite:Miller's Anesthesia 9e Ch 41]