Reducing Operating Room Infections from the Top Down
HVAC recommendations in the proposed 2006 AIA Guidelines for Design and Construction of Hospital and Healthcare Facilities seek to lessen the number of surgical-site infections.
Surgical-site infections (SSIs) are the third most frequently reported type of iatrogenic infection. SSIs have been estimated to result in $1 billion to $10 billion in direct and indirect medical costs each year, as reported by Susan Cantrell in Healthcare Purchasing News , March 2006 ( www.hpnonline.com/inside/2006-03/0603infectionconnection.html ).
Quoted in that article, Dr. Ronald Lee Nichols of the Tulane University School of Medicine highlighted several important factors in SSIs:
"The most critical factor in post-operative infection is the sound judgment and proper technique of the surgical team and the general health and disease state of the patient. Other factors influence the development of post-operative wound infection, especially in clean procedures, for which the infection rate (less than 3%) is generally low. Infections in these patients may be due solely to airborne exogenous microorganisms." (For more on this topic, see "Emerging Infectious Diseases," Mar-Apr 2001, www.cdc.gov/ncidod/eid/vol7no2/nichols.htm ).
Alhough the risk of infection is proportionately small when compared with successful surgery outcomes, even a low infection rate is too high. Hospitals may soon be required to disclose infection rates. For example, as reported by Allison Aubrey on May 11, 2006 in her story "States push to disclose hospital infection rates," on NPR's Morning Edition, Pennsylvania is now requiring every hospital to disclose infection rates. Quoted in that report, Marc Volavka, director of Pennsylvania's Health Care Cost Containment Council, hopes to spare future patients from hospital-acquired infections.
The 2006 AIA hospital and health-care guidelines are referenced by architects, engineers and health-care professionals throughout the United States and in other countries who are planning new or renovated health-care construction. Authorities in 42 states, the Joint Commission for the Accreditation of Healthcare Organizations and several federal agencies use the guidelines as a reference code or standard when reviewing construction designs and plans and completed health-care facilities.
The 2006 draft of the guidelines proposes that changes should be made to the design standards of operating rooms, specifically air-diffusion strategies, that should minimize the risk of wound-site infection. Additionally, ASHRAE is working on a rough proposal—Standard 170, Ventilation of Health Care Facilities —that will corroborate the AIA guidelines proposed changes.
Following the new HVAC rules
The current 2001 AIA guidelines are not specific about the type of diffusers to be used in operating rooms. They call for supply ceiling outlets located near the center of the work area. Also, at least two air return outlets, located near the floor level in two locations as remotely from each other as practical, are required. Ceiling diffusers currently installed in ORs vary from one health-care institution to another. Some use standard aspirating diffusers—diffusers that entrain room air—some use a mix of linear and non-aspirating diffusers, and some use all non-aspirating diffusers, which direct air downward from the ceiling without entraining room air.
The draft version of the 2006 guidelines recommends using non-aspirating diffusers with a face velocity of 25 to 35 feet per minute to be located near center of the work area.
A paper titled "Comparison of Operating Room Ventilation Systems in the Protection of Surgical Sites" (Memarzadeh and Manning, ASHRAE Transactions 108 [Pt.2], 2002) suggests that the main factor in ventilation system design is control of the operating room's central region. The authors concluded that the diffuser array should be large enough to cover the main heat-dissipating objects.
In light of these recommendations, careful coordination is essential among the medical equipment team, the medical staff, the architect, the mechanical engineer and the electrical engineer. The goal is to design a diffuser array large enough to include properly placed ceiling-mounted medical equipment—surgical lights, boom, columns, monitors, etc.—and room lighting to cover the area occupied by the surgical team. This array should provide a unidirectional flow pattern in the work area, forcing the particulates to be removed from the surgical site. Essentially, the medical equipment location must be optimized to accommodate diffuser placement above the center work area.
Memarzadeh and Manning also call for the primary supply diffuser array to be installed as follows:
"The airflow shall be unidirectional and downwards, and the average velocity of the diffusers shall be 25 to 35 fpm. The diffusers shall be concentrated to provide an airflow pattern over the patient and surgical team."
"The area of the primary supply diffuser array shall be an area that extends 12 to 18 in. on each side beyond the footprint of the surgical table. Up to 30% of the primary supply diffuser array area may be allocated for non-diffuser uses such as lights, gas columns, etc."
"Additional supply diffusers may be required to provide additional ventilation to the OR to achieve environmental requirements relating to temperature, humidity, etc. "
"The room shall be provided with at least two low sidewall return grilles, with the bottom of these grilles installed approximately 6 in. above the floor."
The proposed AIA guidelines also call for a more unidirectional airflow, which won't mix the air in the room. Instead, air—and the contaminants within—will be forced away from the surgical table toward air returns located near the floor. At least two air returns are still mandated. Air movement reduction will diminish the quantity of contaminants and keep air turbulence down. In this way, the system will work on the same principle as that of a cleanroom. The application of the proposed guidelines in the construction of new ORs should help minimize the numbers of wound-site infections.
Impact on users
Passage of this proposal, which is expected in early summer, will impact virtually every new and remodeling surgical facility project. However, existing surgical centers are typically grandfathered in and may not need to be remodeled.
Additionally, these proposed 2006 guidelines changes in OR air distribution are the first major changes in more than 20 years. It will take time for state or local building codes to adopt the new guidelines.
For some mechanical engineers and facility owners, this proposed change may mean business as usual, as their standard design practices already take into account the changes proposed in the 2006 guidelines.
Regardless, these requirements will potentially impact the way surgical room engineers design future ORs, as the options available to the designers are now limited.
Design engineers, architects and facility owners need to anticipate the necessary changes to accommodate surgical equipment on the ceiling, along with specified materials and additional construction costs.
In the end, hopefully the increase in costs as a result of the new design standards may be balanced by fewer lawsuits associated with surgical-site infections. But because some SSIs may be caused by particles that enter the body through the wound site and should be preventable with better airflow in the surgical room and proper filtration, the proposed guidelines are in the best interest of health-care facilities and the patients they care for.