HVAC System in the Operating Room
This Design Guide continues to recommend 100 % outside air for Surgical HVAC systems. Air change CFM requirements are
increased to a minimum of 20 air changes per hour. This increase reflects the fact that a minimum of 20 air changes are necessary in
modern surgical rooms to handle the generated cooling load.
VA experience, based on historical data collection of surgical performance measures, demonstrates the VA systems and practices
provide outcomes equivalent to the best in the industry. The VA ventilation system provides equivalent performance to the system
recommended by the American Society of Heating, Refrigerating & Air-Conditioning Engineers (ASHRAE) standard which is more
commonly used. The ASHRAE system requires a minimum of 5 air changes of outside air, 20 air changes of recirculated air, for a
minimum total of 25 total air changes in the surgical room. It is recognized that design guides should be tools for discussion for
architects, engineers, designers and health care professionals to use in fashioning facilities to best meet local needs, under the
umbrella of providing the best environment possible for Veterans' health care. Therefore, VA is expanding its data collection on
surgical infection rates and energy usage. Until such time as further study leads to revision of current VA standards, the 100 %
outside air requirement remains in effect.
Supply Air: In addition to keeping the remaining Operating Room as clean as possible, the air supply system must be designed to
minimize the entrance of airborne bacteria into the sterile field as well as the area occupied by the anesthesiology staff. This is
accomplished by washing these areas with a vertical column of slow moving sterile air emanating from a supply air plenum directly
above the operating table. In addition to this plenum, a surrounding array of slot diffusers is adjusted to direct the air at an outward
angle toward the perimeter of the Operating Room. A pseudo-laminar flow system is the desired result.
It is highly desirable to identify the supply air zone described above by installing a patch of flooring material that is a different color
from the rest of the room. This patch should be located in the center of the Operating Room by aligning it with the slot diffusers
above. This will indicate the sterile field.
Air supplied to the Operating Room as mentioned above is supplemented with additional clean air entering the Operating Room from
the clean core. Operating Rooms and Clean Corridors shall both be maintained under positive pressure.
Exhaust Air/Return Air: During an operation, all of the space from the floor itself to a distance 15'' (380 mm) above is considered
contaminated. Therefore, all exhaust/return grilles must be positioned low on the wall approximately 18'' (460 mm) above floor. The
Operating Room exhaust system should include a minimum of two low exhaust/return air grills located in opposite corners to
minimize recirculation of contaminated air within the Operating Room.
Design Guide - Surgical Service
Page 11 of 14
Date: August 2005
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