Phrenic nerve function and its relationship to atelectasis after coronary artery bypass surgery.

Atelectasis following coronary artery bypass surgery (CAB) occurs in the majority of patients. To determine the importance of operative variables in the development of postoperative atelectasis and the incidence of phrenic nerve injury caused by topical cold cardioplegic solution, we studied 57 patients (53 male, four female) undergoing CAB. Their mean age, +/- SD, was 58 +/- 13 years. Transcutaneous stimulation was used to evaluate phrenic nerve function preoperatively and postoperatively in 52 patients. An unequivocal paresis of the phrenic nerve was documented in five patients. In an additional 27 patients, the amplitude of the compound diaphragm action potential was reduced postoperatively. However, methodologic limitations did not allow the conclusion that this was secondary to a phrenic axonal degeneration. Discriminant analysis of intraoperative variables showed more severe atelectasis with a larger number of grafts, with a longer operative and bypass time, when the pleural space was entered, when a right atrial drain and a cardiac insulating pad were not used, and with a lower body temperature. It is concluded that phrenic paresis may occur after CAB and topical cold cardioplegia, but that other factors must explain the atelectasis found in the majority of patients.