Air Barrier System for the Prevention of Surgical Site Infection (ABS)

Airborne particles are present in all indoor environments including the operating room. Most of these particles come from the surgical staff moving around in the room, positioning of the patient during surgery, and the movement of surgical equipment and supplies. While the amount of particulate in an operating room is much, much less than is found in a typical home or public space, some particulate is usually present no matter how the room and air are cleaned and filtered. Typically these few particulate cause no problems, but the goal is always to have the cleanest air possible during surgery. The Air Barrier System (ABS) consists of a reusable blower and a sterile nozzle. The blower feeds filtered air into the sterile disposable nozzle, which disperses a constant stream of gentle, high purity air over the surgical incision. This stream of air forms a shield over the surgical area to prevent airborne particulate from settling into the open wound. This is particularly critical for long-duration surgeries, such as procedures that involve the implantation of a prosthesis. The main objective of this research study is to determine whether the ABS can reduce the potential for surgical site infection during total hip replacement, spinal fusion, or lower extremity bypass grafting procedures. These procedures were chosen because each is a long-duration procedure which involves implantation of prosthesis.

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.

The Air Barrier System will be employed throughout the surgical procedure for this group of patients.

ABS is a device that emits a stream of purified air over the surgical site creating a barrier that prevents the intrusion of bacteria.

Fewer patients in the Air Barrier System group will have implant infection compared to the Control group. Diagnosis of SSI was made by a physician who was masked to the patients' group assignment and not involved in the patients' care by evaluating medical records using the standard and extremely widely used (clinically, epidemiologically, and in research) CDC criteria*, which categorize SSI into superficial incisional, deep incisional, and organ/space/implant levels. Superficial and deep incisional infections were defined and reported as "incisional" infections, whereas organ/space/implant level infections were defined and reported as "implant" infections. *See Mangram AJ, et al. Guideline for prevention of surgical site infection, 1999: Hospital Infection Control Practices Advisory Committee. Infect Control Hosp Epidemiol 1999;20:250-278.

Comparison of Levels of Airborne CFU Measured at Incision Sites Between the Control and Air Barrier System Groups

Airborne CFU samplers will be used to monitor bacterial populations at the location immediately adjacent to the surgical site. Air will be drawn through a length of PVC tubing onto agar plates at ten minute intervals. Plates will be incubated for 36 hours at 35 degrees Celsius. Staining and morphological identification will be used to identify and count viable bacteria.

Patient will be clinically evaluated to identify potential implant SSI through daily visits during the hospital stay, at subsequent clinic visits and hospital stays, or telephonically on a monthly basis for one year. If encounter indicates the potential presence of SSI, physician will make diagnosis of SSI using the CDC criteria. Organ/space/implant level infections were defined and reported as "implant" infections.

Patient will be clinically evaluated to identify potential incisional SSI through daily visits during the hospital stay, at subsequent clinic visits and hospital stays, or telephonically on a monthly basis for one year. If encounter indicates the potential presence of SSI, physician will make diagnosis of SSI using the CDC criteria. Superficial and deep incisional infections were defined and reported as "incisional" infections.

Inclusion Criteria: This study will recruit adult patients undergoing total hip arthroplasty, lumbar fusion with instrumentation, or femoral-popliteal bypass graft surgical procedures. Exclusion Criteria: The presence of any of the following factors will exclude patients from enrollment in the study: History of prior prosthesis infection Active infection.

Darouiche RO, Green DM, Harrington MA, Ehni BL, Kougias P, Bechara CF, O'Connor DP. Association of Airborne Microorganisms in the Operating Room With Implant Infections: A Randomized Controlled Trial. Infect Control Hosp Epidemiol. 2017 Jan;38(1):3-10. doi: 10.1017/ice.2016.240. Epub 2016 Oct 26.