Study reveals how OR ventilation, patient positioning impact surgical site infection risk

Editor's Note

Optimizing patient positioning can help reduce the risk of surgical site infections due to airborne contaminants in positive-pressure ORs, according to a study published August 12 in Nature: Scientific Reports.

Maintaining higher pressure than adjacent spaces prevents entry of contaminants from environments external to the OR. For this study, researchers used computational fluid dynamics to help identify the optimum overpressure for efficient operation while reducing the risk of surgical site infections (SSIs). Based on comparisons of four OR schemes for patient location, they concluded that a modified 90-degree angle, significantly reduces contaminant concentrations (CO2 and particles) in the OR. This optimized positioning, aligned with the proper arrangement of exhaust outlets, plays a crucial role in minimizing the risk of SSIs.

Other key findings include:

• The number and positioning of surgical staff significantly impacted air quality and contaminant levels. The study evaluated eight different configurations with varying numbers of staff and supply velocities. It was found that the OR could maintain acceptable cleanliness levels with up to ten staff members, provided the supply velocity was at least 0.53 m/s or 33 air changes per hour (ACH). However, improper positioning of staff, particularly near exhaust outlets, could create turbulence and hinder contaminant removal, thereby increasing the risk of SSIs.
• Although surgical masks contributed to a cleaner environment around the operating table, they did not significantly alter the overall particle dispersion paths. 
• Supply velocity and ACH were found to be critical parameters in maintaining optimal room pressure and cleanliness. The research recommends a supply velocity of 0.56 m/s, room pressure of 5.89 Pa, and 35 ACH for the investigated OR to achieve the best balance between cleanliness and the operational efficiency of the ventilation system. Higher velocities and pressures led to overpressure issues, which could reduce fan efficiency, increase noise and vibration, and potentially shorten the lifespan of the HVAC system.
• Researchers proposed modifying the supply surface area to manage overpressure effectively. Enlarging the supply area allowed for lower supply velocities while maintaining high positive room pressure and achieving the desired ACH. This modification resulted in a cleaner environment without negatively impacting the ventilation system’s efficiency or lifespan, further reducing the risk of SSIs.