## Clinical Recognition of Malignant Hyperthermia **Key Point:** The constellation of sudden hypertension, tachycardia, muscle rigidity, and rising core temperature during volatile anesthetic exposure in the immediate post-intubation period is pathognomonic for malignant hyperthermia (MH). **High-Yield:** Malignant hyperthermia is a pharmacogenetic disorder of skeletal muscle calcium regulation triggered by exposure to succinylcholine and/or volatile anesthetics (isoflurane, sevoflurane, desflurane). The triggering agents cause uncontrolled calcium release from the sarcoplasmic reticulum, leading to sustained muscle contraction, hypermetabolism, and a cascade of complications. ### Pathophysiology In susceptible individuals, volatile anesthetics and depolarizing neuromuscular blockers bind to the ryanodine receptor (RYR1) or CACNA1S mutations, causing: 1. Uncontrolled calcium efflux from sarcoplasmic reticulum 2. Sustained muscle contraction (rigidity) 3. Hypermetabolism → heat production 4. Rhabdomyolysis → myoglobinuria, hyperkalemia, acute kidney injury 5. Disseminated intravascular coagulation (DIC) ### Immediate Management Algorithm ```mermaid flowchart TD A[Suspected MH: Rigidity + Hypertension + Tachycardia + Rising Temp]:::urgent --> B[STOP volatile agent immediately]:::action B --> C[Hyperventilate with 100% O₂]:::action C --> D[Call for dantrolene sodium]:::action D --> E[Prepare dantrolene: 2.5 mg/kg IV bolus]:::action E --> F[Repeat every 5 min if signs persist]:::action F --> G[Active cooling: cold IV saline, ice packs, cold peritoneal lavage]:::action G --> H[Monitor: K⁺, CK, myoglobin, urine color, DIC panel]:::outcome H --> I[Post-op: ICU monitoring, repeat dantrolene q4-6h × 24-48h]:::action ``` **Clinical Pearl:** Early recognition and immediate discontinuation of the triggering agent is the single most important intervention. Dantrolene acts by blocking calcium release from the sarcoplasmic reticulum via the ryanodine receptor, halting the cascade. Each 2.5 mg vial must be reconstituted with 60 mL sterile water (no bacteriostatic agents) — this is time-critical and requires rapid pharmacy/nursing coordination. ### Why Option 1 Is Wrong Continuing isoflurane while treating hypertension with labetalol is catastrophic. The triggering agent remains in the circuit, perpetuating calcium dysregulation and heat production. Sympathomimetic response is secondary to the underlying MH crisis; treating only the blood pressure ignores the primary pathology. ### Why Option 3 Is Wrong Reducing isoflurane concentration does not eliminate the trigger. MH is dose-independent — even low concentrations of volatile agents will perpetuate the crisis in susceptible patients. Nifedipine is ineffective for MH and delays definitive therapy. ### Why Option 4 Is Wrong Switching to sevoflurane is incorrect because sevoflurane is ALSO a triggering agent for MH. All volatile anesthetics (isoflurane, sevoflurane, desflurane, halothane) are contraindicated in MH-susceptible patients. The only safe maintenance agents are TIVA (propofol + remifentanil) or nitrous oxide with opioids. **Mnemonic:** **STOP MH** — **S**top volatile agent, **T**otal IV anesthesia or safe agents, **O**xygen 100%, **P**repare dantrolene; **M**onitor labs (K⁺, CK, myoglobin), **H**eat management (active cooling). **Warning:** Dantrolene is NOT a sedative or muscle relaxant in the conventional sense — it is a specific antagonist of MH. Its use is diagnostic and therapeutic. Failure to recognize and treat MH within minutes results in mortality rates of 5–10% and severe morbidity (rhabdomyolysis, DIC, acute kidney injury, hyperkalemic cardiac arrest). ## Epidemiology & Risk Factors - **Incidence:** 1:10,000–1:15,000 anesthetics in susceptible populations - **Genetics:** Autosomal dominant inheritance; RYR1 mutations (most common), CACNA1S mutations - **Family history:** Strong predictor; first-degree relatives have ~50% risk - **Age at presentation:** Can occur at any age; most common in children and young adults ## Post-Operative Management - Admit to ICU for continuous cardiac monitoring - Aggressive fluid resuscitation (target urine output 200–300 mL/h to prevent myoglobin precipitation in renal tubules) - Repeat dantrolene 1 mg/kg IV every 4–6 hours for 24–48 hours to prevent recrudescence - Monitor for complications: hyperkalemia (peaked T waves, widened QRS), rhabdomyolysis (elevated CK >5000 IU/L), DIC (PT/PTT, fibrinogen, D-dimer), acute kidney injury - Arrange MH testing (caffeine halothane contracture test or genetic testing) for the patient and first-degree relatives post-operatively [cite:Gupta Ch 40 - Malignant Hyperthermia]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.