What is myasthenia gravis? Is this patient at risk of pulmonary aspiration of gastric contents? How would you assess this preoperatively? Should she receive pharmacologic prophylaxis? Which drugs? Are there any interactive effects with her current medications?

Is it important to know which steroid she is on? Should she be “covered” for surgery? Should she receive her pyridostigmine preoperatively? Would you base your management on an assessment of her pulmonary function tests?

She is very anxious; how would you counsel her about preoperative sedation? She wants a mask induction; is that OK? What endpoints would you look for to determine the onset of anesthesia? What if she goes into laryngospasm during induction – how will you manage it?

Myasthenia gravis (MG) is a neuromuscular disease that is caused by circulating antibodies that block acetylcholine receptors at the postsynaptic neuromuscular junction, inhibiting the excitatory effects of acetylcholine on nicotinic receptors. The disease leads to fluctuating muscle weakness and fatigue.

It is important to know what type of steroid she is on and how much she has been taking. The hypothalamic-pituitary-adrenal axis is often suppressed by exogenous administration of a glucocorticosteroid. The effect depends on the maintenance dose of steroid that the patient is on. The patient will need stress dose coverage when the maintenance daily dose is greater than 10 mg of prednisone (or equivalent). There are arguments against the need for stress dose steroids if patients have been on daily maintenance doses of less than 10 mg of prednisone (or equivalent) or if the child has had very minor surgery where the actual stress to the patient is minimal. If one chooses not to give a stress dose, the patient should be carefully monitored for lethargy or hypotension in the postoperative period – both of which could be signs of glucocorticoid deficiency. I will administer steroid coverage for this particular patient because she is scheduled for a sternotomy. Ideally, the patient should not take her pyridostigmine preoperatively. Omitting the morning dose of pyridostigmine will weaken the patient and obviate the need for intraoperative muscle relaxants in most cases. Added weakness may provoke her anxiety so the issue should be carefully discussed prior to the day of surgery. Yes, if pulmonary function is impaired despite optimal medical therapy, the morning dose of pyridostigmine would be indicated. Standard pulmonary function tests should be normal when the myasthenia is well controlled with medical therapy. If myasthenia is not well controlled, the forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV₁) are decreased due to weakness. If FVC is normal and the FEV₁ is decreased, it may indicate intrathoracic airway obstruction due to an enlarged thymus and may portend difficulty when the patient undergoes positive pressure ventilation.

Depending on how weak the patient is, preoperative intravenous anxiolytics may be administered with caution and close monitoring for respiratory depression. Yes, there is no contraindication to an inhalation induction, provided the patient is appropriately NPO and there is no history of reflux-related aspiration pneumonia in the past. Due to weakness of the extraocular muscles, the loss of response to eyelash stimulation is not as helpful as general stimulation to determine the onset of general anesthesia in this particular patient. Similarly, testing of the muscle twitch may be falsely absent or diminished around the eyes as opposed to ulnar nerve stimulation. If the patient develops laryngospasm, it can be overcome with simply applying positive pressure, particularly in the presence of weak pharyngeal muscles. Alternatively, due to the deficiency of acetylcholine receptors, a small dose of nondepolarizing muscle relaxant (or a large dose of succinylcholine) is administered to relax the glottic muscles.

What are your monitoring considerations? Does this patient need an arterial line? Why? Should the patient have central access? Why? Are there circumstances in which a pulmonary artery catheter would help?

Assuming an intravenous induction, which agents will you choose? Any advantage for propofol? Etomidate? Explain your choice. Should the patient undergo a mask induction with a volatile agent and breath spontaneously? Explain your choice of inhalation agent.

Assume that you have administered a dose of propofol and started sevoflurane; the patient is now in laryngospasm and her saturation is 85 %. There is no ETCO₂ on the monitor. What would you do? Would succinylcholine be safe to give? How do myasthenic patients respond to succinylcholine? Should the patient receive a nondepolarizing agent? How much should be given? Which nondepolarizer would you choose?

The patient was successfully intubated and is oxygenating well. Your blockade monitor indicates no twitches, yet the patient moves when the median sternotomy begins. The surgeon insists that you have to relax the patient. Which relaxant would you give and how much would you give? How will you judge the efficacy of your muscle relaxant? How do you use a blockade monitor for a myasthenic patient?

During the thymus dissection, the patient begins wheezing, and you note a prolonged and slow upstroke to the exhalation CO₂ curve on the capnograph. What are your considerations? How do you diagnose the problem? Albuterol inhalation through the endotracheal tube does not help. With an FiO₂ of 1.0, the O₂ saturation is 92 % and the ETCO₂ waveform is small and prolonged. What would you do now? The wheezing is better when the surgeons stop operating. Would endobronchial intubation help? Would a double-lumen tube be indicated? What would you tell the surgeons?