Pneumonia after cardiac surgery is predictable by tracheal aspirates but cannot be prevented by prolonged antibiotic prophylaxis

Background. The purpose of this study was to assess the value of tracheal a spirate as a predictor of pneumonia after coronary artery bypass grafting a nd to evaluate the efficacy of prolonged perioperative antibiotic prophylax is. Methods. Tracheal aspirates of 500 patients undergoing coronary artery bypa ss grafting were taken immediately after intubation and analyzed for microo rganisms by Gram stain and semiquantitative microbiologic cultures. All pat ients received 2 g ceftriaxone as a single-dose perioperative antibiotic pr ophylaxis before operation. Results of Gram stains were available before the patients were transferred to the intensive care unit. After the results were known, both groups of pa tients (positive Gram stain, group I; negative Gram stain, group 2) were ra ndomly assigned to either conventional antibiotic prophylaxis (A), consisti ng of ceftriaxone 2 g on postoperative day 1, or prolonged antibiotic proph ylaxis (B), with ticarcillin + clavulanic acid 3 x 5.2 g during 72 hours. R esults. From 500 patients, 91 had a positive Gram stain whereas 409 had a n egative one. The incidence of pneumonia was significantly higher in patient s with preoperative positive tracheal aspirates (15.3%) than in patients wi th a negative one (3.6%; p < 0.01). However, prolonged prophylaxis did not reduce the rate of postoperative pneumonia, which was as high as 13% in unt reated positive patients versus 17% in treated positive patients, and 2% in untreated negative patients versus 4% in treated patients. In patients who had pneumonia, there was a high correlation between the microorganisms fou nd in preoperative aspirates and those observed when aspirates were repeate d (100% correlation in patients with conventional antibiotic prophylaxis an d 87% in those with prolonged prophylaxis). Conclusions. Early postoperative pneumonia (< 7 days) is most likely caused by microorganisms that colonize the respiratory tract before operation. Th e risk of pulmonary infection after coronary artery bypass grafting can be predicted from the preoperative tracheal aspirates. Prolonged perioperative antibiotic prophylaxis has no efficacy in reducing the incidence of pulmon ary infections. (C) 2001 by The Society of Thoracic Surgeons.