A 32-year-old male patient is scheduled for an emergency laparotomy for acute appendicitis. He has a history of malignant hyperthermia (MH) in his father. During induction, the anesthesiologist avoids volatile anesthetics and uses total intravenous anesthesia (TIVA). For neuromuscular blockade, which muscle relaxant would be the SAFEST choice for this patient?

Explanation

## Safe Muscle Relaxant Choice in Malignant Hyperthermia Susceptibility **Key Point:** In patients with a family history of malignant hyperthermia (MH), both depolarising agents (succinylcholine) and some non-depolarising agents carry risk. Atracurium is the safest choice because it undergoes Hofmann elimination and ester hydrolysis, independent of organ function and MH susceptibility. ### Why Atracurium is Safe in MH-Susceptible Patients Atracurium's unique pharmacokinetics make it ideal: - **Hofmann elimination:** Temperature and pH-dependent spontaneous degradation in plasma - **Ester hydrolysis:** Non-specific esterase metabolism - **No organ dependence:** Does not rely on hepatic or renal function - **No MH trigger:** Atracurium has never been implicated in MH crises ### Comparison of Muscle Relaxants in MH Susceptibility | Agent | Type | MH Risk | Metabolism | Notes | | --- | --- | --- | --- | --- | | **Succinylcholine** | Depolarising | **HIGH** | Plasma pseudocholinesterase | **CONTRAINDICATED** — potent MH trigger | | **Rocuronium** | Non-depolarising | **LOW** | Hepatic (60%), renal (40%) | Acceptable but organ-dependent | | **Atracurium** | Non-depolarising | **NONE** | Hofmann + ester hydrolysis | **GOLD STANDARD** in MH | | **Mivacurium** | Non-depolarising | **LOW** | Plasma pseudocholinesterase | Acceptable but less ideal than atracurium | **High-Yield:** Succinylcholine is an absolute contraindication in MH-susceptible patients; it is a potent trigger of fulminant MH crisis. Depolarising agents should never be used in confirmed or suspected MH families. **Clinical Pearl:** The combination of TIVA (propofol/remifentanil) + atracurium + avoidance of volatile anesthetics represents the "MH-safe" anesthetic technique. Dantrolene should be immediately available. **Mnemonic:** **SAFE agents in MH** — **S**uccinylcholine is **UNSAFE**, **A**tracurium is **ALWAYS safe**, **F**entanyl-based TIVA, **E**scape volatiles. ## Mechanism of MH Triggering Malignant hyperthermia is an autosomal dominant pharmacogenetic disorder affecting calcium regulation in skeletal muscle (mutations in RYR1 or CACNA1S genes). Succinylcholine causes sustained depolarisation and uncontrolled calcium release, leading to: 1. Sustained muscle contraction (rigidity) 2. Hypermetabolism and heat generation 3. Rhabdomyolysis, hyperkalemia, acidosis 4. Cardiac arrhythmias and potential cardiac arrest Non-depolarising agents do not trigger this cascade, but atracurium's organ-independent metabolism makes it the preferred choice.