Effects of two regimens of antibiotic prophylaxis on colonizing flora of the respiratory tract in patients with cardiovascular surgery

Introduction

Antibiotic prophylaxis in cardiovascular (CV) surgery has greatly reduced the rate of postoperative infections. First-generation or second-generation cefalosporines are used for this purpose. Our hospital changed its antibiotic prophylaxis protocol for elective CV surgery in June 2007 from cefuroxime to cefazolin in accordance with national guidelines [1]. The aim of this study was to explore the effect of changing this antibiotic prophylaxis protocol on microbial flora in sputum.

Methods

Retrospective study. All patients admitted >10 days on the ICU after elective CV surgery between 1 June 2006 and 1 June 2007 (Group 1) were compared with the same group of patients between 1 July 2007 and 1 August 2008 (Group 2). Patients received single-dose prophylaxis (bypass surgery), or 2 days of prophylaxis (cardiac prosthetic surgery). Group 1 received cefuroxime and Group 2 received cefazolin. Patients did not receive selective digestive tract decontamination. Isolated pathogens from elective sputum cultures of all patients were registered and compared between groups after dividing pathogens into six classes based on the profile of intrinsic antibiotic susceptibility. Comparative data between groups were analyzed with Pearson's Χ test.

Results

One hundred and fifty-eight patients had positive sputum cultures. Comparing total amounts of positive cultures, there was no significant difference between colonization with pathogenic micro-organisms between Group 1 (n = 77 patients) and Group 2 (n = 76 patients). In Group 1 more colonization with pathogens from class 4 (β-lactamase-producing Enterobacteriaceae and Pseudomonas aeruginosa) was observed compared with Group 2 (45% vs 34%, P = 0.079). This nonsignificant difference between groups was mainly attributable to a difference in colonization with Pseudomonas. In the other classes of pathogens, no differences were observed. No difference in postoperative wound infections was noted between groups.

Conclusions

Prophylactic use of cefazolin instead of cefuroxime after CV surgery resulted in a trend towards reduction of colonization of the respiratory tract with intrinsic β-lactam-resistant microbial flora in patients with prolonged ICU stay, without adverse effects on the incidence of postoperative wound infection.