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

From the Guidelines

Anesthesia in patients with myasthenia gravis requires careful planning and medication adjustments, with a preference for regional anesthesia and close neuromuscular monitoring. The anesthesiologist should avoid using long-acting neuromuscular blocking agents and instead opt for short-acting agents like succinylcholine or reduced doses (50-75% of normal) of intermediate-acting agents such as atracurium or cisatracurium, as suggested by the guidelines on muscle relaxants and reversal in anesthesia 1.

Key Considerations

• Preoperative optimization includes continuing anticholinesterase medications (pyridostigmine) until the morning of surgery, as discontinuing them increases the risk of respiratory distress 1.
• Volatile anesthetics should be used cautiously as they potentiate muscle weakness.
• For induction, propofol (1.5-2.5 mg/kg) or etomidate (0.2-0.3 mg/kg) can be used, while maintenance can be achieved with propofol infusion (75-150 mcg/kg/min) or sevoflurane/desflurane at reduced concentrations.
• Opioids should be used judiciously, with remifentanil (0.05-0.2 mcg/kg/min) being a good option due to its short half-life.
• Postoperatively, patients should be closely monitored for respiratory complications, with anticholinesterase medications resumed as soon as possible.

Rationale

Myasthenia gravis causes acetylcholine receptor antibodies to reduce available receptors at the neuromuscular junction, making these patients extremely sensitive to neuromuscular blockers and at higher risk for postoperative respiratory failure, as noted in the clinical practice guidelines for sustained neuromuscular blockade in the adult critically ill patient 1. The guidelines on muscle relaxants and reversal in anesthesia also highlight the importance of monitoring neuromuscular blockade in patients with neuromuscular disease, such as myasthenia gravis 1.

Medication Adjustments

• A 50-75% reduction in the recommended dose of non-depolarizing muscle relaxants, such as atracurium and cisatracurium, is common and correlates with the severity of myasthenia, as suggested by the guidelines on muscle relaxants and reversal in anesthesia 1.
• The use of succinylcholine may require increased doses due to resistance, while non-depolarizing muscle relaxants may have increased sensitivity and duration of action.
• Evaluation of the TOF ratio by EMG in the hypothenar hand muscles prior to muscle relaxant administration can predict sensitivity to non-depolarising muscle relaxants and guide dosage adjustments 1.

From the FDA Drug Label

In patients with myasthenia gravis or myasthenic (Eaton-Lambert) syndrome, small doses of nondepolarizing neuromuscular blocking agents may have profound effects. In such patients, a peripheral nerve stimulator and use of a small test dose may be of value in monitoring the response to administration of muscle relaxants. In patients who are known to have myasthenia gravis or the myasthenic (Eaton-Lambert) syndrome, small doses of vecuronium bromide may have profound effects. In such patients, a peripheral nerve stimulator and use of a small test dose may be of value in monitoring the response to administration of muscle relaxants

The considerations for anesthesia in a patient with myasthenia gravis (MG) include:

• Using small doses of nondepolarizing neuromuscular blocking agents to avoid profound effects
• Utilizing a peripheral nerve stimulator to monitor the response to administration of muscle relaxants
• Administering a small test dose to assess the patient's response to the muscle relaxant 2 3 Key considerations for patients with MG include careful dose adjustment and close monitoring to minimize the risk of prolonged neuromuscular blockade and other complications.

From the Research

Considerations for Anesthesia in Myasthenia Gravis Patients

• Myasthenia gravis (MG) is an autoimmune disease that interferes with neuromuscular transmission, making patients at risk of postoperative residual curarization (PORC) if nondepolarizing muscle relaxants are used 4.
• The use of rocuronium and sugammadex as a neuromuscular blockade reversal agent has been shown to be effective in MG patients undergoing surgery, with rapid and predictable recovery from neuromuscular blockade 4, 5, 6.
• However, there have been cases where sugammadex failed to reverse neuromuscular blockade in MG patients, highlighting the importance of monitoring neuromuscular blockade and considering alternative reversal agents such as neostigmine 7.
• Sugammadex has been shown to be effective in reversing rocuronium-induced neuromuscular blockade in MG patients, with a rapid recovery time of around 100-200 seconds 4, 5, 6.
• The use of rocuronium and sugammadex in MG patients undergoing thymectomy has been evaluated, with results showing a rapid recovery of neuromuscular function and no signs of postoperative residual curarization or respiratory depression 4, 6.

Special Considerations

• MG patients are at risk of hypoventilation and postoperative bronchopneumonia due to clinically inapparent insufficient muscle strength, making it essential to monitor peripheral capillary oxygen saturation (SpO2) and partial pressure of carbon dioxide (pCO2) closely 4.
• The use of sugammadex in MG patients has been shown to be generally well-tolerated, but its effectiveness may be unpredictable in some cases, emphasizing the need for careful monitoring and consideration of alternative reversal agents 7, 8.
• The management of cholinesterase inhibitors is crucial in the perioperative period of myasthenic patients, and the use of sugammadex should be considered in conjunction with careful monitoring of neuromuscular blockade 7.