What is the recommended anesthetic management for a patient with a history of masseter muscle spasm during previous anesthesia?

Anesthetic Management for Patient with History of Masseter Muscle Spasm

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. 1

Understanding the Clinical Significance

Masseter muscle spasm following succinylcholine administration is recognized as a warning sign of MH susceptibility and may represent a prodromal indication of developing MH. 1 The Association of Anaesthetists guidelines emphasize that in MH-susceptible patients, jaw muscle rigidity may be exaggerated in both degree and duration, and rigidity may extend to other muscle groups. 1 Importantly, patients can have multiple uneventful anesthetics before experiencing an MH reaction, so previous uncomplicated exposures do not exclude MH susceptibility. 1

Mandatory Anesthetic Approach

Trigger Avoidance

• Absolutely avoid all volatile inhalational anesthetic agents (sevoflurane, desflurane, isoflurane, halothane). 1
• Absolutely avoid succinylcholine (the depolarizing muscle relaxant). 1
• Use TIVA with propofol or other intravenous agents for induction and maintenance. 1
• Non-depolarizing muscle relaxants, benzodiazepines, opioids, and nitrous oxide are safe. 2

Anesthetic Workstation Preparation

The workstation must be prepared to eliminate residual volatile anesthetics to achieve inspired concentrations ≤5 ppm: 1

• Remove all vaporizers from the anesthetic workstation. 1
• Change the entire breathing circuit (T-circuit, circle circuit, reservoir bag) and soda lime canister for uncontaminated equipment. 1
• 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). 1
• 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. 1

Monitoring and Safety Measures

Intraoperative Monitoring

• Standard anesthetic monitoring is sufficient if trigger-free anesthesia is provided—no special monitoring is required beyond routine practice. 1
• Have dantrolene immediately available (at least 36-50 ampoules for an adult, 20 mg per ampoule mixed with 60 ml sterile water). 1

Laboratory Testing

• Preoperative blood tests are not routinely necessary for MH-susceptible patients. 1
• Consider measuring creatine kinase, potassium, and myoglobin if there is history of elevated resting CK, muscular symptoms (cramps, myalgia), or rhabdomyolysis. 1

Outpatient Surgery Considerations

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. 1 This approach has been safely performed for decades in MH diagnostic centers for muscle biopsies. 1

Critical Pitfalls to Avoid

Common Errors

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

Emergency Preparedness

If MH crisis develops despite precautions: 1

• 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)
• Monitor for minimum 24 hours in ICU/HDU setting

Post-Anesthetic Counseling

Following this anesthetic, the patient should: 2

• Receive counseling about MH susceptibility
• Obtain a MedAlert bracelet
• Be registered with the Malignant Hyperthermia Association
• Have family members informed of potential hereditary risk (autosomal dominant inheritance with variable penetrance)
• Consider referral for definitive caffeine-halothane contracture testing of muscle biopsy 2, 4