Abstract
Several investigators have proposed criteria to predict the need for postoperative mechanical ventilation in patients with myasthenia gravis. Kimura et al. recently described the Shinshu University scoring system which is applied to Japanese patients. They identified eight risk factors-myasthenia and/or cholinergic crisis, respiratory disease, bulbar palsy, thymoma, operability, other complications, pyridostigmine dosage, and % vital capacity.
We tested the value of this scoring system retrospectively in 74 patients with myasthenia gravis who recieved thymectomy. Sixty-four patients out of 74 (86.5%) were predicted accurately by the scoring system. However, six patients, predicted not to need controlled ventilation, needed prolonged postoperative ventilatory support. Of these 6 patients, two had seriously reduced % vital capacity of less than 59%, one had a progressive exacerbation of myasthenic symptoms before surgery, and one encountered bulbar weakness with menstruation.
This study aimed to propose new criteria and a modified scoring system. We applied the statistical technique of multivariate discriminant analysis to select the most useful preoperative variables for identifying with myasthenia gravis patients who need mechanical ventilation. Using this new scoring system, a prediction of the postoperative need for ventilatory support was accurately achieved in 94.6%, and false negative could be reduced in only two cases.
