What is the effect of reducing the air change rate on the ventilation effectiveness in ultra-clean operating rooms?

Background The operating room (OR) department is one of the most energy-intensive departments of a hospital. The majority of ORs in the Netherlands have an air-handling installation with an ultra-clean ventilation system. However, not all surgeries require an ultra-clean OR. Aim To determine the effect of reducing the air change rate on the ventilation effectiveness in ultra-clean ORs. Methods Lower air volume ventilation effectiveness (VE Lv ) of conventional ventilation (CV), controlled dilution ventilation (cDV), temperature-controlled airflow (TcAF) and unidirectional airflow (UDAF) systems were evaluated within a 4 × 4 m measuring grid of 1 × 1 m. The VE Lv was defined as the recovery degree (RD), cleanliness recovery rate (CRR) and air change effectiveness (ACE). Findings The CV, cDV Lv and TcAF Lv ventilation systems showed a comparable mixing character in all areas (A, B and AB) when reducing the air change rate to 20/h. Ventilation effectiveness decreased when the air change rate was reduced, with the exception of the ACE. At all points for the UDAF-2 Lv and at the centre point (C3) of the TcAF Lv , higher RD 10Lv and CRR Lv were measured when compared with the other examined ventilation systems. Conclusions The ventilation effectiveness decreased when an ultra-clean OR with an ultra-clean ventilation air-supply system was switched to an air change rate of 20/h. Reducing the air change rate in the OR from an ultra-clean OR to a generic OR will reduce the recovery degree (RD 10 ) by a factor of 10–100 and the local air change rate (CRR) by between 42% and 81%.