Operating Theatre Ventilation Systems and Their Performance in Contamination Control: "At Rest" and "In Operation" Particle and Microbial Measurements Made in an Italian Large and Multi-Year Inspection Campaign

Abstract

In Operating Theatres (OT), the ventilation system plays an important role in controlling airborne contamination and reducing the risks of Surgical Site Infections (SSIs). The air cleanliness is really crucial in this field and different measurements are used in order to characterize the situation in terms of both airborne microbiological pollutants and particle size and concentration. Although the ventilation systems and airborne contamination are strictly linked, different air diffusion schemes (in particular, the Partial Unidirectional Airflow, P-UDAF, and the Mixing Airflow, MAF) and various design parameters are used, and there is still no consensus on real performance and optimum solutions. This study presents measurements procedures and results obtained during Inspection and Periodic Performance Testing (1228 observations) in a large sample of Italian OTs (175 OTs in 31 Italian hospitals) in their operative life (period from 2010 to 2018). The inspections were made after a cleaning procedure, both in "at-rest" conditions and "in operation" state. Inert and microbial contamination data (in air and on surfaces) are analyzed and commented according to four relevant air diffusion schemes and design classes. Related data on Recovery Time (RT) and personnel presence were picked up and are commented. The results confirm that the ventilation systems are able to maintain the targeted performance levels in the OT operative life. However, they attest that significant differences in real OT contamination control capabilities do exist and could be ascribed to various design choices and to different operation and maintenance practices. The study shows and confirms that the air diffusion scheme and the design airflow rate are critical factors. Beside large variations in measurements, the performance values, in terms of control of airborne particle and microbial contamination (in air and on surfaces), for P-UDAF systems are better than those that were assessed for the MAF air diffusion solution. The average performances do increase with increasing airflows, and the results offer a better insight on this relationship leading to some possible optimization.

Keywords: microbiological contamination; mixing airflow; operating theatres; particle contamination; unidirectional airflow; ventilation systems.

Figure 1

Average airborne particle concentration vs. ACH in “at-rest” conditions for the 175 investigated OTs. Cumulated values for particles ≥0.5 µm.

Figure 2

Average microbiological air contamination vs. air changes per hour (ACH) in “at-rest” conditions for the 175 investigated OTs.

Figure 3

Recovery Time vs. ACH in “at-rest” conditions. Values of the 175 investigated OTs.

Figure 4

Average microbiological air contamination vs. ACH in “operational” conditions for the 175 investigated OTs.

Figure 5

Average microbiological air contamination vs. personnel crowd index in “operational” conditions for different ventilation systems. Values for 175 investigated OTs.

Figure 6

Average microbiological surface contamination in different OT locations under “at rest” conditions after cleaning procedures. Position 1 = surgical table, Position 2 = scialytic lamp, Position 3 = surgical instruments table, Position 4 = anesthesia tower.