Aim. The aim of this study was to assess the influence of the true operating room (OR) ventilation on the risk of revision due to infection after primary total hip arthroplasty (THA) reported to the Norwegian Arthroplasty Register (NAR). Method. 40 orthopedic units were included during the period 2005 – 2015. The Unidirectional airflow (UDAF) systems were subdivided into small-area, low-volume, vertical UDAF (lvUDAF) (volume flow rate (VFR) (m. 3. /hour) <=10,000 and diffuser array size (DAS) (m. 2. ) <=10); large-area, high-volume, vertical UDAF (hvUDAF) (VFR >=10,000 and DAS >=10) and Horizontal UDAF (H-UDAF). The systems were compared to conventional, turbulent ventilation (CV) systems. The association between revision due to infection and OR ventilation was assessed using Cox regression models, with adjustments for sex, age, indication for surgery, ASA-classification, method of fixation, modularity of the components, duration of surgery, in addition to year of primary THA. All included THAs received systemic, antibiotic prophylaxis. Results. 51,292 primary THAs were eligible for assessment. 575 (1.1%) of these THAs had been revised due to infection. Compared to CV, there was similar risk of revision due to infection after THA performed in ORs with lvUDAF (RR=0.9, 95 % CI: 0.7–1.1) and with H-UDAF (RR=1.3, 95 % CI: 0.9–1.8). The risk of revision due to infection after THA performed in ORs with large-area hvUDAF-systems was lower (RR=0.8, 95% CI: 0.6–0.9, p=0.01) compared to CV. Conclusions. This study indicates that large-area, high-volume, vertical UDAF systems may be superior to conventional ventilation systems as a prophylactic measure against THA infection. This emphasizes the importance of assessing the big diversity of different ventilation systems when studying effect measures

Introduction. Infection is disastrous in arthroplasty surgery and requires multidisciplinary treatment and debilitating revision surgery. Between 80-90% of bacterial wound contaminants originate from colony forming units (CFUs) present in operating room air, originating from bacteria shed by personnel present in the operating environment. Steps to reduce bacterial shedding should reduce wound contamination. These steps include the use of unidirectional laminar airflow systems and the introduction of theatre attire modelled on this principle (e.g. total body exhaust suits). Our unit introduced the use of the Stryker Sterishield Personal Protection System helmet used with laminar flow theatre systems. This study compares an enclosed helmet system used with standard gowns, with standard hood and mask attire. Method. 12 simulated hip arthroplasties were performed, six using disposable sterile impermeable gown, hood and mask and a further 6 using a Sterishield helmet and hood. Each 20 minute operation consisted of arm and head movements simulating movements during surgery. Air was sampled at wound level on a sterile draped operating table using a Casella slit sampler, sampling at 700l/minute. Samples were incubated on Blood agar for 48 hours at 37°c and the CFUs grown were counted. Results. Mean number of CFUs for the helmet was 9.33 with hood and mask attire having 49.16 CFUs (S. Ds 6.34 and 26.17; p value 0.0126). In all cases a coagulase negative staphylococcus was isolated. Conclusion. Although the sample size was small, we demonstrated a fivefold increase in the number of CFUs shed when using hood and mask attire compared to personal helmet and sterile hood. We conclude that the helmet system is superior to non-sterile hood and mask at reducing bacterial shedding by theatre personnel