Effects of operating room layout and ventilation system on ultrafine particle transport and deposition

The main role of Heat Ventilation and Air Conditioning (HVAC) systems in Operating Rooms (ORs) is to ensure the desired thermo-hygrometric conditions and indoor air quality, minimizing the risk of air contamination. The main sources of contamination inside ORs, during surgical operations, are Colony-Forming Units (CFUs), fine particles and ultrafine particles (UFPs), which could cause surgical site infections or health issues for the medical staff. The present work aims at increasing the scientific knowledge concerning numerical modelling of the UFP transport and deposition in ORs, analysing the effectiveness of three different ventilation systems. A numerical methodology, validated in previous works, has been used to study UFP transport and deposition inside three actual ORs, two of them equipped with a Laminar AirFlow (LAF) system and one with a Turbulent Mixing Airflow (TMA) system. Both the LAF and the TMA systems effectively evacuate the UFPs, ensuring a particle deposition rate significantly lower than the evacuation rate. The installation of extraction grilles near the surgical table allows obtaining an improvement of UFP evacuation. Due to the not perfect symmetry of OR layouts and surgical wound position, a preferred way for UFP transport can be observed. The instrument table position should be chosen consequently, to reduce UFP, CFU and contaminant deposition. The UFP concentrations at surgical staff head height cannot be neglected for health-related risks.