How are patients with MG premedicated for surgery?
Optimization of the myasthenic patient’s
condition can markedly reduce the risk of surgery. Ideally, surgery is
performed during a period of remission when all other medical problems are
optimized. Careful preoperative eval-uation of respiratory parameters and
bulbar strength are necessary before prescribing premedication. Respiratory
muscle strength may be quantified through pulmonary function tests (i.e., tidal
volume, vital capacity, maximum breathing capacity, and inspiratory force).
Premedication should be used with caution and avoided in patients with bulbar
symptoms or respiratory difficulty. Anxiolysis may be achieved with small doses
of benzodiazepines in those patients whose myasthenia is under good control.
Opioid avoidance is sometimes recommended to prevent depressed respiratory
drive from further interfering with the potential for respiratory failure based
on myasthenic or cholinergic crisis.
Administration of anticholinesterases
preoperatively remains controversial. Some authors advocate withholding
anticholinesterases before surgical and anesthetic proce-dures that require
muscle relaxation. The patient’s baseline weakness facilitates muscle
relaxation, requiring little or no exogenous neuromuscular blockade. Withholding
anti-cholinesterases decreases the risk of drug interactions later. Such
interactions include partial antagonism of non-depolarizing muscle relaxants
and prolongation of the action of succinylcholine. Additionally, withholding
anti-cholinesterases eliminates cholinergic crisis as a cause of postoperative
respiratory failure. This approach does not work well for those patients who
are physically or psycho-logically dependent on anticholinesterases. Other
authors feel that these drugs may be given preoperatively without interfering
significantly with anesthetic and postoperative management.
The relative immobility associated with
hospitalization and surgery may produce a reduced requirement for
anti-cholinesterases.
Steroids should be continued in the
perioperative period for those patients on chronic therapy.
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