Impact of laminar air flow on operating room contamination, and surgical wound infection rates in clean and contaminated surgery

The study took place at 917-beds Italian teaching hospital with 15 Operating Rooms (OR), from January 2001 to December 2013. To evaluate the potential impact of LAF, the surveillance period has been divided into two phases: 2001–2003 period, with ORs equipped with low-turbulence displacement air flow supply air systems, versus the 2004–2013 period, with ORs equipped with laminar air flow supply. Relevant information was collected by physicians of the Hospital Hygiene Service as follows: type of procedure, perioperative antibiotic prophylaxis administration, duration of procedure, wound contamination class, and patient's ASA score. Microbiological laboratory data, and readmission episodes were used for post-discharge surveillance. A Surface Air System sampler was used to assess air microbial contamination; at least 7 samplings (minimum one cubic meter, each) at 5–10 min of distance have been taken. Environmental sampling on surfaces was carried out by RODAC surface plates, and contact of at least 10 s. Air particulate count was assessed by continuous samplings at 1,5 m from the floor at the center of the room, or near the surgeon. Two multivariable logistic regression models, stratified by contamination class (clean plus clean contaminated, and contaminated plus dirty wounds), were designed to evaluate the potential, independent effect of OR ventilation system, adjusting for factors usually associated to SSI. Selection of the variables to be included in the final logistic regression analysis was based on bivariate associations between the selected variables and SSI. During the study period, 71,655 surgical procedures underwent epidemiological surveillance, with a cumulative incidence of SSI of 2.26% (N = 1618), with significant differences between the two periods. The average, and maximum number of particles in the OPERATIONAL setting were significantly higher during Period A with respect to Period B, as well as bacterial contamination of the operating table and of surgical light. Independent risk factors for SSI at multivariate analysis included patients' increasing ASA score, and duration of the procedures; while procedures performed under the LAF system, and those receiving adequate antibiotic prophylaxis were at lower risk of developing SSIs. Moreover, LAF was protective along all the considered contamination classes, after adjusting for other variables, ranging from OR 0.57 (95%CI, 0.48–0.68) in clean and clean contaminated surgery, to OR 0.31 (95%CI, 0.17–0.56) in contaminated and dirty surgery. The results show that procedures performed with adequate antibiotic prophylaxis,5 and under an active LAF ventilation system were at reduced risk of infection, independently from other well-established risk factors. In fact, LAF was effective among both clean, and contaminated/dirty surgical procedures, thus adding to the literature that has sometimes reported conflicting results. The protective role of the LAF is in accordance with other studies where authors found lower bacterial and particle concentration in operative fields in surgical procedures under LAF6, 7 and 8 also if the direct correlation between particulate and microbial contamination has been debated.9 The results also support the findings that the level of bacteria is correlated with duration of surgery in clean procedures.10 Despite the lack of evidence of direct influence of air quality in the single procedure, the present study is reinforced by the large number of procedures included, under real-operational conditions. Nevertheless, we have to highlight that in the above experience, no major changes in professional behavior, as well as in other not-controlled infection control measures, have occurred between the two periods under study. Creating safe environments and monitoring their performances is crucial in securing patients safety.