What are the anesthesia considerations for a patient with myasthenia gravis (MG) undergoing surgery?

Anesthesia Considerations for Myasthenia Gravis

Patients with myasthenia gravis require a 50-75% dose reduction of non-depolarizing muscle relaxants (atracurium, cisatracurium, rocuronium) due to their heightened sensitivity, and succinylcholine should be avoided due to paradoxical resistance requiring higher doses. 1

Muscle Relaxant Selection and Dosing

Non-Depolarizing Agents (Preferred)

• Use rocuronium, atracurium, or cisatracurium at 50-75% of standard doses due to increased sensitivity and prolonged duration of action in MG patients. 1
• The dose reduction correlates directly with disease severity—more severe MG requires greater reductions. 1
• Rocuronium at doses ≥0.9 mg/kg can be used for rapid sequence intubation when necessary, though at reduced total dose. 2
• Benzylisoquinoline agents (atracurium/cisatracurium) are preferred in patients with concurrent renal or hepatic impairment due to organ-independent elimination. 1, 2

Succinylcholine (Avoid)

• Succinylcholine demonstrates paradoxical resistance in MG patients, requiring increased doses to achieve the same effect due to down-regulation of acetylcholine receptors. 1
• This resistance creates unpredictable dosing requirements and should be avoided. 1

Avoiding Muscle Relaxants Entirely

• Consider avoiding muscle relaxants altogether when feasible, using deep inhalational anesthesia (desflurane) with propofol and remifentanil for intubation. 3
• This approach eliminates concerns about residual neuromuscular blockade but requires careful titration to ensure adequate surgical conditions. 3

Mandatory Neuromuscular Monitoring

Quantitative neuromuscular monitoring with train-of-four (TOF) ratio measurement is mandatory when any muscle relaxant is used in MG patients. 1, 2

Pre-administration Assessment

• Measure baseline TOF ratio before administering muscle relaxants—if TOF <0.9 at baseline, sensitivity to non-depolarizing agents is significantly greater and doses must be further reduced. 1
• This pre-operative TOF measurement predicts individual patient sensitivity and guides initial dosing. 1

Intraoperative Monitoring

• Use continuous TOF monitoring throughout the procedure to avoid overdosing. 1
• Monitor the adductor pollicis muscle (hand) as standard practice. 1
• Patients with primarily ocular MG may require higher doses than those with generalized disease, necessitating individualized titration. 1

Reversal Strategy

Sugammadex is the preferred reversal agent for rocuronium-induced neuromuscular blockade in MG patients, not neostigmine. 1, 2

Why Sugammadex Over Neostigmine

• Neostigmine interferes with chronic anticholinesterase therapy (pyridostigmine) that MG patients receive. 1
• Sugammadex provides rapid, predictable, and complete reversal—achieving TOF >0.9 in approximately 117 seconds on average. 4
• In a series of 117 MG patients, sugammadex resulted in zero cases of residual curarization, reintubation, or postoperative pneumonia. 4

Perioperative Medication Management

Anticholinesterase Therapy

Continue pyridostigmine on the day of surgery, including the morning dose—discontinuing it increases the risk of respiratory distress and muscle weakness. 5, 6

• Omitting the morning dose causes 43% of patients to experience respiratory discomfort preoperatively and increases sensitivity to vecuronium unpredictably. 6
• Continuing pyridostigmine provides relative resistance to muscle relaxants (requiring slightly higher doses) but maintains baseline muscle strength. 6

Drugs to Avoid

• Aminoglycosides and fluoroquinolones worsen neuromuscular transmission and must be avoided. 5
• Beta-blockers, calcium channel blockers, and magnesium-containing compounds can exacerbate weakness. 5, 7
• Atracurium and mivacurium have prolonged effects due to pyridostigmine's inhibition of plasma cholinesterase. 1

Anesthetic Agent Selection

Induction and Maintenance

• Propofol is preferred for induction due to its short duration allowing rapid respiratory assessment, though it may cause hypotension. 5
• Sevoflurane or isoflurane are safe inhalational agents for maintenance. 1
• Dexmedetomidine provides sedation with minimal respiratory depression, making it suitable for MG patients. 5

Analgesia

• Short-acting opioids like remifentanil or fentanyl are preferred (duration 3-10 minutes), allowing quick assessment of respiratory function. 1, 5
• Avoid morphine and codeine due to potential for prolonged respiratory depression. 1

Postoperative Considerations

Extubation Criteria

• Ensure TOF ratio >0.9 before extubation to confirm complete reversal of neuromuscular blockade. 1, 4
• Monitor for adequate tidal volumes, negative inspiratory force, and ability to sustain head lift. 4

Risk Factors for Prolonged Ventilation

The degree of sensitivity to muscle relaxants does NOT predict need for postoperative ventilation. 8 Instead, these clinical factors do:

• History of previous respiratory crises (odds ratio 3.5) predicts prolonged ventilation need. 8
• Presence of bulbar palsy (odds ratio 3.7) increases risk of postoperative respiratory support. 8
• Disease severity and preoperative respiratory function are more important than intraoperative muscle relaxant sensitivity. 8

Monitoring Requirements

• Standard recovery room care is appropriate if trigger-free anesthesia was provided. 1
• Continuous monitoring of respiratory rate, depth, oxygen saturation, and level of consciousness is essential. 5
• Watch for signs of myasthenic crisis (increasing weakness, dysphagia, respiratory distress) in the first 48-120 hours postoperatively. 4

Regional Anesthesia Alternative

Regional anesthesia (spinal, epidural, peripheral nerve blocks) or local anesthesia is an excellent choice for MG patients when surgically appropriate, completely avoiding the risks associated with muscle relaxants and general anesthesia. 1