Effect of switching off unidirectional downflow systems of operating theaters during prolonged inactivity on the period before the operating theater can safely be used

Background: Switching off air handling systems in operating theaters during periods of prolonged inactivity (eg, nights, weekends) can produce a substantial reduction of energy expenditure. However, little evidence is available regarding the effect of switching off the air handling system during periods of prolonged inactivity on the air quality in operating theaters during operational periods. The aim of this study is to determine the amount of time needed after restarting the ventilation system to return to a stable situation, with air quality at least equal to the situation before switching off the system. Methods: Measurements were performed in 3 operating theaters, all of them equipped with a unidirectional downflow (UDF) system. Measurements (particle counts of emitted particles with a particle size ≥0.5 μm) were taken during the start-up of the ventilation system to determine when prespecified degrees of protection were achieved. Temperature readings were taken to determine when a stable temperature difference between the periphery and the protected area was reached, signifying achievement of a stable condition. Results: After starting up the system, the protected area achieved the required degrees of protection within 20 minutes (95% upper confidence limit). A stable temperature difference was achieved within 23 minutes (95% upper confidence limit). Both findings lie well within the period of 25 minutes normally required for preparations before the start of surgical procedures. Conclusions: Switching off the ventilation system during prolonged inactivity (during the night and weekend) has no negative effect on the air quality in UDF operating theaters during normal operational hours.

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