Air Barrier System for the Prevention of Surgical Site Infection

Surgical site infection (SSI) following prosthesis implantation and other invasive procedures is a serious complication leading to increased mortality, morbidity, and financial cost to patients and the U.S. healthcare infrastructure. Multiple studies have shown that the primary source of surgical site bacterial colonization is staphylococci shed from the skin of people present in the surgical theatre. These bacteria-carrying skin cells are aerosolized into the environment and deposit into surgical incisions. The innovations currently pursued in research and industry to combat nosocomial infection fall primarily into three categories: (1) developing new antimicrobial drugs and agents, (2) developing antimicrobial coatings for devices, and (3) implementing procedures to reduce the risk of cross-contamination. Significant resources are being allocated to prevent infections from developing post-operatively and to mitigate the effects of infection once microorganisms enter the body. However, there is little development of new technologies that can be employed in the operating room to prevent the initial intrusion into the surgery site. All modern surgical theatres utilize some form of air filtration. In a conventional flow system, air streams mix freely in the room. In an OR designed for laminar flow (LFOR), air emits from filters and proceeds into the room in relatively coherent streams. The benefit thought to be achieved by a LFOR, in principle, is that filtered air does not mix with contaminated air before reaching the surgery area. The difficulty in achieving the desired results in a LFOR lies in the fact that once the flow pattern enters the room, it is subjected to a very complex set of dynamics over a significant distance. Air is clean upon leaving the filter bank, but it enters a space laden with airborne bacteria and particulate matter shed from people in the OR. Nimbic Systems has developed a device, the Air Barrier System (ABS), which shields surgical sites from airborne contaminants in the operating room by creating a localized clean air field directly adjacent to and surrounding the incision site. The ABS consists of two components: a Filter and an air Nozzle with attached Hose. The Filter is a nonsterile reusable component which filters ambient operating room air and forces it through an exit port on the top of the unit. The Nozzle is attached on top of the incision drape adjacent to a surgical incision with Velcro® fastening pads. The end of the Hose is plugged into the Filter's air exit port. Contaminant-free air then flows through the Hose and Nozzle over the incision site. The ABS maintains this protective envelope of bacteria-free air over a wide range of patient and incision site geometries, yet the insertion of hands and instruments are not disrupted by the protective envelope. The ABS technology was extremely successful at reducing the presence of bacteria and other colony forming units at incision sites during Phase I study. In a randomized, prospective clinical study of 36 hip arthroplasty procedures, the ABS reduced the presence of colony forming units at incision sites by 84% versus ambient operating room levels. This will be a prospective randomized double-blind pilot trial of the ABS in three surgical specialty applications (total hip arthroplasty, lumbar laminectomy with instrumentation, and femoral-popliteal bypass graft). A cohort of 300 recruited patients will be randomly assigned, at a 1:1 ratio, to either a control group (no ABS) or experimental group (with ABS). The primary outcome of the trial is the occurrence of SSI by one year after surgery using the established CDC definitions and classifications of surgical site infection. Secondary outcomes include (1) measuring levels of colony forming units (CFU) present in the operating room air during surgical procedures to examine correlations with occurrence of SSI; (2) examining types of organisms that cause SSI in the two study groups; and (3) surgeon satisfaction with the ABS device. Patient characteristics and measures of operating room environment will be collected during surgery, and the patients' surgical sites will be clinically evaluated following surgery to identify potential superficial or deep SSI up to one year after surgery. The estimated occurrence of SSI in the control group is 6%, based on baseline data pertaining to the three studied types of surgery at the Michael E. DeBakey VA Medical Center. The anticipated rate of SSI in the experimental group is 3%. The proposed pilot study is designed to detect a clinically relevant reduction (i.e., a 50% reduction, from 6% to 3%) in the observed rate of SSI in patients who are exposed to the ABS vs. no ABS. The results of this proposed pilot trial will be used to construct a subsequent pivotal prospective, randomized, multi-center clinical trial.