What is the total air changes per hour and minimum outdoor air changes per hour in the OTs?
Air changes are largely for the control of airborne organisms by dilution. Way back in the 1970’s 15 air changes of 100% outside air was the norm and mandate. (Srichitra Medical Centre, Trivandrum & Hinduja Hospital, Mumbai). In 1974, studies were made in two running neurosurgical operating theaters at St Mary’s Hospital, Rochester, MN under a research grant from U.S. Dept. of Health. The theatres had turbulent air distribution systems and established that the variable airborne particulates in the theatre were at least 30% more in the case of 15 100% outside air changes as compared to 25 recirculated changes with 30% being outside air. It was also seen that 25-30 air changes produced optimum results. Figure 1 shows the trend lines. ASHRAE revised the guidelines thereafter to 5 outside air changes out of 25 total air changes. In an operating theatre, the greatest amount of contamination is generated by the operating team, as result of their activities during surgery.
