MYASTHENIA
GRAVIS
A 56-year-old man with myasthenia gravis (MG) affect-ing
extraocular and bulbar musculature presents for trans-cervical thymectomy. He
is taking pyridostigmine 660 mg and prednisone 20 mg orally every day in
divided doses. He is also taking metoclopramide 10 mg four times a day for
reflux esophagitis. Spirometry reveals a vital capacity of 50% predicted and an
FEV1/FVC ratio of 80%. Maximum breathing capacity is 45% predicted.
Following placement of monitors and while the patient is breathing 100% oxygen,
rapid sequence induction with cricoid pressure is performed using thiopental 4
mg/kg and succinylcholine 1 mg/kg. After 60 seconds, twitch height is decreased
by 60%, and the trachea is intubated with some difficulty. Anesthesia is
maintained with nitrous oxide, oxygen, and sevoflurane as required. Ventilation
is controlled. At return of twitch height to 100%, vecuronium 0.05 mg/kg is
administered with resultant loss of twitch response to nerve stimulation.
Surgery lasts 11/2 hours. The anesthetic agents are discontin-ued,
and the patient demonstrates four equal twitches to train-of-four (TOF)
stimulation. Neostigmine 0.06 mg/kg and glycopyrrolate 0.01 mg/kg are
administered. When the patient responds to command, the trachea is extubated,
at which point the patient immediately becomes dyspneic.
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