Describe a reasonable anesthetic technique for a patient with MG undergoing transcervical thymectomy

Describe a reasonable anesthetic technique for a patient with MG undergoing transcervical thymectomy.

All patients undergoing anesthetic care should have a continuous electrocardiogram, blood pressure, pulse oximeter, end-tidal carbon dioxide, peripheral nerve stim-ulation (when relaxants are used or weakness is antici-pated), and inspired oxygen monitoring. In general, additional monitoring is dictated by surgical requirements and coexisting disease. Induction of anesthesia follows denitrogenation with 100% oxygen and proceeds with injection of a short-acting rapid-onset barbiturate, propo-fol, or etomidate.

Tracheal intubation and controlled ventilation are essen-tial in these patients. Muscle relaxation for tracheal intuba-tion is often not required but may be facilitated by ventilation with potent inhalation agents. If succinylcholine is used for rapid airway control, 2 mg/kg may be required and can have a prolonged duration of action. Despite the well-recog-nized resistance of myasthenics to succinylcholine, usual clinical doses, which exceed 5 times the ED₉₅, produce adequate relaxation for endotracheal intubation, making dosing unpredictable. Some authors feel that muscle relax-ants are best avoided in these patients, recommending that potent inhaled agents will provide adequate relaxation for most procedures. Some patients may not tolerate the cardiovascular depression associated with these agents and may require a balanced technique with muscle relaxants. Small incremental doses of intermediate-acting nondepolar-izing muscle relaxants may be titrated with the assistance of peripheral nerve stimulation. Vecuronium, cisatracurium, and mivacurium have short elimination half-lives and may not require antagonism at the end of surgery.

Residual postoperative neuromuscular blockade pres-ents another controversy. Some feel that continued ventila-tion until adequate strength has returned is the safest management for these patients. Others feel that anti-cholinesterases (with an antimuscarinic) may be titrated in small doses to nerve stimulation response. Administration of excessive amounts of an anticholinesterases risks cholin-ergic crisis. The decision to antagonize residual postopera-tive neuromuscular blockade must be individualized, and the risk of cholinesterase inhibitors (cholinergic crisis, bradydysrhythmias, and increased secretions) must be weighed against the risk of postoperative ventilation. Respiratory distress may be treated intravenously with 1/30th of the usual oral pyridostigmine dose.

Other factors with slight neuromuscular blocking prop-erties can take on additional importance in the face of con-comitant MG (Table 27.1).

Tracheal extubation is often predicated on a tidal vol-ume of 6 mL/kg, negative inspiratory force of –25 cm H₂O, vital capacity of 15 mL/kg, and sustained head-lift for 5 seconds.