A 28-year-old woman with a family history of anesthetic complications undergoes elective cesarean section under general anesthesia. After induction with thiopental and intubation with succinylcholine, the surgeon notes generalized muscle rigidity and the patient's temperature rises to 39.2°C within 8 minutes. ETCO₂ rises to 58 mmHg. Urine output is dark brown. Which of the following is the MOST important immediate intervention?

Explanation

## Malignant Hyperthermia in Perioperative Setting ### Recognition of Crisis **Key Point:** The constellation of rapid-onset muscle rigidity, hypercarbia (ETCO₂ 58), fever (39.2°C), and dark urine in the context of succinylcholine exposure is diagnostic of acute malignant hyperthermia. Family history of anesthetic complications is a major risk factor. ### Pathophysiology ```mermaid flowchart TD A[Succinylcholine exposure]:::action --> B[Abnormal ryanodine receptor function] B --> C[Uncontrolled Ca²⁺ release from SR] C --> D[Sustained muscle contraction] D --> E[Hypermetabolism & Heat production] E --> F[↑ ETCO₂, ↑ Temperature, Acidosis] C --> G[Muscle breakdown] G --> H[Hyperkalemia, Myoglobinuria] H --> I[Dark urine, Acute kidney injury risk] J[Dantrolene 2.5 mg/kg IV]:::action --> K[Block SR Ca²⁺ release] K --> L[Halt muscle contraction] L --> M[Reverse hypermetabolism] ``` ### Why Dantrolene Is Mandatory | Aspect | Detail | |--------|--------| | **Mechanism** | Ryanodine receptor antagonist; blocks calcium-induced contraction at the SR | | **Onset** | 1–5 minutes IV; effects peak at 5–10 minutes | | **Dosing** | Initial 2.5 mg/kg IV; repeat q5 min up to 10 mg/kg total | | **Preparation** | Each 20 mg vial requires 3 mL sterile water; reconstitute immediately | | **Efficacy** | Reduces mortality from ~80% to <5% when given promptly | | **Contraindication** | None in acute MH crisis — benefits far outweigh risks | **High-Yield:** Dantrolene is the ONLY pharmacologic agent that addresses the root cause of MH (abnormal calcium handling). All other interventions are supportive. **Clinical Pearl:** Dark urine indicates myoglobinuria from rhabdomyolysis. This patient is at imminent risk of acute kidney injury and disseminated intravascular coagulation (DIC). Aggressive fluid resuscitation must accompany dantrolene administration. ### Concurrent Actions 1. **Stop all triggering agents** — discontinue succinylcholine and any volatile anesthetic immediately 2. **Hyperventilate with 100% O₂** — reduce ETCO₂ and improve oxygenation 3. **Active cooling** — ice packs, cold IV fluids, cold peritoneal lavage if available 4. **Treat hyperkalemia** — calcium gluconate (cardioprotection), insulin + glucose, sodium bicarbonate 5. **Aggressive hydration** — target urine output 200–300 mL/hr to prevent myoglobin precipitation in renal tubules 6. **Monitor for DIC** — coagulation studies, platelet count, fibrinogen **Mnemonic:** **DANTRO** — **D**iscontinue triggering agents, **A**dminister dantrolene, **N**euromuscular monitoring, **T**reat hyperkalemia, **R**apid cooling, **O**xygenate aggressively. ### Post-Crisis Follow-Up - Refer patient and first-degree relatives for MH susceptibility testing (caffeine halothane contracture test or RYR1/CACNA1S genetic testing) - Document MH diagnosis in medical record and alert patient to wear MedicAlert bracelet - Future anesthetics: use TIVA (propofol + opioid), avoid succinylcholine and volatile agents - Consider regional anesthesia for future surgeries when feasible [cite:Miller's Anesthesia 8e Ch 33] [cite:Stoelting's Pharmacology and Physiology in Anesthetic Practice 5e Ch 32]