BACTERIOSTATIC BREATHING CIRCUIT FILTRATION DOES NOT EFFECT POST-OPERATIVE WOUND INFECTION RATES IN CARDIAC SURGERY

Abstract

S138 INTRO: Numerous studies have reported anesthesia machine [1,2] and breathing circuit [2,3] bacterial contamination. Some investigators have suggested the organisms contaminating the anesthesia machines may be partly responsible for post-operative wound infections [3]. High efficiency microbial filters have been found effective in preventing cross contamination from machine to patient and from patient to machine when placed at the Y connector of a standard circle system [3]. This study was designed to determine if breathing circuit bacteriostatic filtration is effective in reducing the incidence of post operative wound infections in patients presenting for elective cardiac surgery. METHODS: Institutional IRB approval was obtained. All adult patients presenting for elective cardiac surgery were randomized to one of two groups. Group FIL had an intertech HEPA filter (Sims Medical Systems, Keene, NH) (filtration efficiency=99.9999+%) placed at the Y Connector of the anesthesia circle system. Group NoF had no filtration or heat/moisture exchange devices. Institutional standards for pre-operative antibiotic treatment and sterile patient preparation were uniform for both patient groups. A power analysis was conducted prior to the start of the study to determine the number of patients necessary to detect a 50% reduction in post-operative wound infections (alpha=0.05, beta=0.2). Statistical significance was determined using Fishers exact test. RESULTS: A total of 259 patients were randomized: 117 patients into group FIL and 142 patients were into group NoF. There were a total of 7 (2.70%)post-operative wound infections: 4 infections (3.42%) in group FIL and 3 infections (2.11%) in group NoF, P=0.62. All were sternal infections, either Staphylococcus epidermidis or Staph. aureus, with equal distribution of pathogens between groups. A post study power analysis was performed to verify sample size selections. Post study power is 0.90. CONCLUSIONS: This study did not demonstrate a reduction in post-operative wound infection rates with the use of bacteriostatic breathing circuit filtration. Although the occurrence of post-operative wound infections is a rare event the sample size and subsequent power analysis of this study allows us to conclude that there is a 90% likelihood that breathing circuit filtration offers no protection against post-operative wound infections. This study was sponsored in part by a grant from Sims Medical Systems, Keene, NH.