Anesthetic Management for Malignant Hyperthermia Susceptible Patients

Introduction to Malignant Hyperthermia Susceptibility

A patient with a history of masseter muscle spasm during previous anesthesia must be treated as malignant hyperthermia (MH) susceptible and receive trigger-free anesthesia with total intravenous anesthesia (TIVA), avoiding all volatile anesthetics and succinylcholine, as recommended by the Association of Anaesthetists 1, 2
Masseter muscle spasm following succinylcholine administration is recognized as a warning sign of MH susceptibility and may represent a prodromal indication of developing MH, with the Association of Anaesthetists guidelines emphasizing that in MH-susceptible patients, jaw muscle rigidity may be exaggerated in both degree and duration 1, 3
Patients can have multiple uneventful anesthetics before experiencing an MH reaction, so previous uncomplicated exposures do not exclude MH susceptibility, according to the Association of Anaesthetists 2, 3

Absolutely avoid all volatile inhalational anesthetic agents (sevoflurane, desflurane, isoflurane, halothane), as recommended by the British Journal of Anaesthesia 1, 4
Absolutely avoid succinylcholine (the depolarizing muscle relaxant), as recommended by the British Journal of Anaesthesia 1, 4
Use TIVA with propofol or other intravenous agents for induction and maintenance, as recommended by the British Journal of Anaesthesia 1, 5

The workstation must be prepared to eliminate residual volatile anesthetics to achieve inspired concentrations ≤5 ppm, as recommended by the British Journal of Anaesthesia 5
Remove all vaporizers from the anesthetic workstation, as recommended by the British Journal of Anaesthesia 1, 5
Change the entire breathing circuit (T-circuit, circle circuit, reservoir bag) and soda lime canister for uncontaminated equipment, as recommended by the British Journal of Anaesthesia 1, 5
Flush the circuit with oxygen or air at maximum flow rate for the workstation-specific time (typically 90 seconds minimum if using activated charcoal filters), as recommended by the British Journal of Anaesthesia 5
Consider using activated charcoal filters on both inspiratory and expiratory limbs if rapid preparation is needed, maintaining fresh gas flow at 3 L/min (not below 1 L/min) and changing filters after 12 hours, as recommended by the British Journal of Anaesthesia 5

Standard anesthetic monitoring is sufficient if trigger-free anesthesia is provided—no special monitoring is required beyond routine practice, as recommended by the British Journal of Anaesthesia 5
Have dantrolene immediately available (at least 36-50 ampoules for an adult, 20 mg per ampoule mixed with 60 ml sterile water), as recommended by the British Journal of Anaesthesia 1, 4
Preoperative blood tests are not routinely necessary for MH-susceptible patients, as recommended by the British Journal of Anaesthesia 5
Consider measuring creatine kinase, potassium, and myoglobin if there is history of elevated resting CK, muscular symptoms (cramps, myalgia), or rhabdomyolysis, as recommended by the British Journal of Anaesthesia 5

MH-susceptible patients may safely undergo outpatient surgery as long as trigger-free anesthesia is provided and a properly prepared "clean" anesthetic workstation is used, as recommended by the British Journal of Anaesthesia 5

Do not assume safety based on previous uneventful anesthetics—MH can occur even after multiple uncomplicated exposures to triggering agents, as recommended by the Association of Anaesthetists 2, 3
Do not use succinylcholine even if previous masseter spasm was isolated without other MH signs—this represents MH susceptibility until proven otherwise, as recommended by the Association of Anaesthetists 2
Do not rely on prophylactic dantrolene as a substitute for trigger avoidance—the cornerstone of management is complete avoidance of triggering agents, as recommended by the British Journal of Anaesthesia 1, 5

If MH crisis develops despite precautions, stop all trigger agents immediately, hyperventilate with 100% oxygen at 2-3 times normal minute volume, administer dantrolene 2 mg/kg IV immediately, repeating until stabilization (may exceed 10 mg/kg maximum), and monitor for minimum 24 hours in ICU/HDU setting, as recommended by the British Journal of Anaesthesia 1, 4