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) 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 was defined as the recovery degree (RD), cleanliness recovery rate (CRR) and air change effectiveness (ACE).

Findings: The CV, cDV and TcAF 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 and at the centre point (C3) of the TcAF, higher RD and CRR 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) by a factor of 10-100 and the local air change rate (CRR) by between 42% and 81%.