A 28-year-old male with a family history of malignant hyperthermia undergoes elective knee arthroscopy under general anesthesia. Fifteen minutes after induction with propofol and intubation with rocuronium, the anesthesiologist notices a sudden rise in end-tidal CO₂ (ETCO₂) from 35 to 65 mmHg, muscle rigidity, and tachycardia (HR 140/min). Which of the following is the most common cause of this acute perioperative crisis?

Explanation

## Acute Perioperative Crisis: Malignant Hyperthermia Diagnosis ### Clinical Presentation Analysis **Key Point:** The constellation of acute rise in ETCO₂, muscle rigidity, and tachycardia in the immediate perioperative period is pathognomonic for malignant hyperthermia. This patient was induced with propofol (non-triggering) and rocuronium (non-depolarizing, non-triggering), but the anesthesia circuit may contain residual volatile anesthetic vapor from previous cases, which is the most common cause of MH in this scenario. ### Early Signs of Malignant Hyperthermia (in order of appearance) | Sign | Timing | Mechanism | |---|---|---| | **↑ ETCO₂** | First (minutes) | Hypermetabolism from uncontrolled muscle Ca²⁺ release | | **Muscle rigidity** | Early (minutes) | Sustained muscle contraction | | **Tachycardia** | Early (minutes) | Sympathetic response to hypermetabolism | | **Tachypnea** | Early (minutes) | Respiratory compensation for metabolic acidosis | | **Arrhythmias** | Early-mid (5–15 min) | Hyperkalemia from muscle breakdown | | **Cyanosis** | Mid (10–20 min) | Hypoxemia from muscle O₂ consumption | | **↑ Core temperature** | LATE (20–30+ min) | Cumulative heat production | | **Rhabdomyolysis** | Late (after 30 min) | Myoglobinuria, acute kidney injury | **Warning:** Temperature rise is a LATE sign. Do NOT wait for fever to diagnose or treat MH. The classic triad of ETCO₂ rise + muscle rigidity + tachycardia is sufficient for diagnosis and immediate intervention. **High-Yield:** In this case, propofol and rocuronium are both non-triggering agents. The trigger must be exogenous: residual volatile anesthetic vapor in the anesthesia circuit from a previous case. This is the most common iatrogenic cause of MH in modern practice. ### Immediate Management Algorithm ```mermaid flowchart TD A["Suspected MH: ↑ETCO₂ + Rigidity + Tachycardia"]:::outcome --> B["STOP all triggering agents"]:::urgent B --> C["Hyperventilate with 100% O₂"]:::action C --> D["Administer dantrolene 2.5 mg/kg IV"]:::action D --> E["Continue dantrolene q 5 min until signs resolve"]:::action E --> F["Active cooling measures"]:::action F --> G["Monitor for complications"]:::outcome G --> H["Check K⁺, CK, myoglobin, urine color"]:::action H --> I["ICU admission for 24–48 hr monitoring"]:::action ``` **Clinical Pearl:** Dantrolene sodium blocks ryanodine receptor-mediated Ca²⁺ release from the sarcoplasmic reticulum. It is the only specific treatment for MH and must be administered immediately. Each vial of dantrolene (20 mg) must be reconstituted with 60 mL sterile water — this is time-consuming, so operating room staff should begin reconstitution as soon as MH is suspected. **Mnemonic — MH Crisis Management:** **STOP-DANT-COOL** = STOP triggering agents, Dantrolene 2.5 mg/kg IV, Active cooling, Notify ICU, Treat hyperkalemia, Check CK/myoglobin, Oxygen 100%, Observe 24–48 hrs, Liaise with MH hotline.