Myasthenia gravis

Myasthenia gravis

Other names	Myasthenia
Anesthetic relevance	High
Anesthetic management
Specialty
Signs and symptoms
Diagnosis
Treatment
Article quality
Editor rating	Comprehensive
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Myasthenia gravis is an autoimmune disease that attacks post-synaptic nicotinic acetylcholine receptors at the NMJ, leading to varying degrees of muscle weakness and fatigue and can affect ocular, bulbar (muscles involved in speech, chewing and swallowing), respiratory, and proximal skeletal muscles. Symptoms are worst at the end of the day or after exertion. Classification of myasthenia depends on whether the patient has only ocular or ocular and non-ocular weakness.

Anesthetic implications

Preoperative optimization

• A steroid listed on a patient’s medication profile indicates a higher risk and elective procedures should be postponed if possible.
• Patients with involvement of respiratory or bulbar muscles tend to have a higher risk for aspiration so pretreatment with metoclopramide or H2 blockers may be helpful. Some MG patients are sensitive to respiratory depressants and premedication with opioids, BZDs, or barbiturates should be considered carefully or not at all.
• IVIG or plasma exchange can be used in emergent cases.
• Diseases associated with MG include DM, thyroid disorders, SLE and RA.
• Patients with MG are resistant to succinylcholine and are exquisitely sensitive to non-depolarizing NMBs.
• Patients should take their morning dose of acetylcholinesterase inhibitor though doing so may result in:
  • Altered patient drug requirements following surgery
  • Increased vagal reflexes
  • Possibility of disrupting bowel anastomoses secondary to hyperperistalsis
  • Significant side effects including salivation, miosis, bradycardia and even cholinergic crisis if given NMB reversal

Intraoperative management

• Of note, IV pyridostigmine is 1/30 of the PO dose.

Postoperative management

• Extubation: performed on awake patients and hopefully close to his/her baseline status. Reinstitute anticholinesterase medication, either by IV infusion or by reimplementation of the patient’s oral regimen.
• Leventhal Criteria: Predictive risk factors for post-operative ventilation support:
  • Disease duration > 6yrs
  • Concomitant pulmonary disease
  • Peak inspiratory pressure < -25 cmH2O
  • Vital capacity < 40 mL/kg (or <2.9L)
  • Pyridostigmine dose > 750 mg/d

• Other indicators include preoperative use of steroids, and previous episode of respiratory failure.
• Drugs to avoid: Calcium Channel blockers, Magnesium, Aminoglycoside antibiotics as all of these may contribute to muscle weakness
• Post-Op Bed: Patients should be monitored in either a ICU or step-down unit but NOT to a conventional surgical ward.