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SUMMARY OF WORKSHOP OBJECTIVES AND CONCLUSIONS I. Current State of Knowledge on Airborne Contamination of Clean Wounds. A. Summary People in the operating room are the major source of operating room airborne bacteria. Each person sheds bacteria from skin and mucous membranes at a relatively constant rate which varies from person to person and which in- creases with increased activity. These bacteria are mainly gram-positive and they are agglomerated on nonliving particles larger than two microns in size. A few individuals shed relatively large numbers of microorganisms into the air and these type-specific bacteria have been associated with postoperative infec- tions of clean wounds. Contamination of clean surgical wounds by microorganisms of the same type found in the operating room air has been demonstrated on repeated occasions. The relationship of this contamination "to subsequent sepsis" is problematical because of the difficulty in separating contamination of the wound by airborne bacteria from contamination from other sources such as the patient or breaks in sterile techniques. B. Conclusions 1. Airborne bacteria in the operating room derive from people and not from the external environment. 2. Airborne bacteria in the operating room do contaminate surgical wounds and are a definite source of infection in clean refined wounds, particularly in high-risk patients and in surgery requir- ing implantation of foreign materials. The degree of their signifi- cance in production of postoperative sepsis has not been quantified. 3. A few people, known as "shedders," persistently shed large numbers of bacteria and have been associated with significantly increased postoperative rates of infection. II. Available Techniques for Estimating Bacterial Contamination of Air. A. Summary Although nonliving airborne concentrations of particulate matter may bear some relationship to airborne bacterial concentrations, it is the concen- tration of airborne microorganisms (as opposed to particles) which is relevant
to the etiology of postoperative sepsis. Therefore, attention will be directed only to techniques which measure the amount of airborne bacterial contamination. 1. Settle Plates - These are sterile agar plates exposed to air for varying periods of time. After incubation, numbers of bacterial colonies are calculated for time exposure and area. Their effi- ciency depends upon direct settling of bacteria or impingement of bacteria carried in air currents onto the agar surface. Settle plates are relatively inexpensive, easy to use, and seem most ap- plicable to the turbulent, low air exchange systems of most modern operating rooms. However, they are probably not accurate in mea- suring bacteria in high-volume directional airflow systems because the physical presence of the plate acts as an air foil which shunts air away from the surface of the plate. 2. Surface Sampling - Using a swab, suction probe, or contact plate, surfaces may be sampled for types of resident bacteria. This is a useful method in determining the amount of environmental fallout of bacteria after exposure of sterile surfaces to the air. 3. Active Air Sampling - Many devices have been developed which actively pump air from the operating theater which is then impinged onto a sterile agar plate, or drawn through sterile liquid culture media, or suctioned through a gelatin membrane of limited pore size. Infor- mation may be obtained relative to particle size and numbers of viable organisms per unit volume of air. However, the volume of air sampled is usually relatively small and organisms may be lost through desic- cation if large volumes are sampled. B. Conclusions 1. Although many methods for sampling airborne bacterial concentrations were described, no paper compared the merits of the various sampling techniques. Information presented at the workshop would not allow recommendation of a specific technique to monitor future evaluations of airborne bacteria.
III. Methods for Reducing Bacterial Contamination of Air A. Summary Methods for reducing the amount of air bacterial contamination in the operating room may be divided into traditional and new categories. 1. Traditional Methods a. Air conditioning systems which provide: 1) air exchange rates of at least 12 per hour; 2) air introduction near ceiling; air exit near floor; 3) mechanical filtration of air before entering room; 4) scheduled filter maintenance; 5) humidity control at approximately 50 percent; 6) temperature control at approximately 70 deg. F. b. Reduction of personnel in operating room. c. Reduction of personnel activity and talking. d. Exclusion of personnel with infection. e. Requirement for all personnel to wear adequate head cover and nose and mouth mask. 2. Newer Methods a. Air conditioning systems 1) clean rooms: unidirectional, high or low velocity, using High Efficiency Particulate Air (HEPA) filters; a) full room or room within a room type; b) horizontal or vertical flow types. 2) local airborne bacteria control a) plastic bubble isolator; b) local high velocity, HEPA filter type (see text); c) ultraviolet light. B. Conclusions 1. There was general agreement that the traditional methods should be recommended for all operating theaters.
2. A specific recommendation for more generalized application of one or more of the newer systems could not be made at this time because of the experimental nature of the systems and the lack of hard statistical data which establishes unequivocably that any of the newer systems in themselves contribute to reduced postoperative infection rates. IV. Effectiveness of Techniques for Controlling Operating Room Airborne Contamination A. Summary As previously noted, it is established that bacterial contamination of the operating room air and sterile surfaces does occur during surgery. A significant portion of the sterile surface contamination results from airborne fallout of bacteria. Quantification of contamination is relatively consistent for each technique in each individual operating room from day to day and case to case. However, the data derived are much less dependable when the amount of contamination is compared between operating rooms or between institutions because of many variables inherent in sampling. These variables include: 1. different operative procedures; 2. different air handling systems; 3. different barrier gown and drape systems; 4. differences in numbers of personnel, personnel activity, and shedding patterns; 5. different sampling and culturing techniques, such as sampling devices, locations of sampling, length of sampling, and differ- ing culture media. For these reasons, the data from individual system evaluations can be accepted but comparison of data for differing systems from different inves- tigators is much more difficult. It should be noted that those papers reporting comparative postoper- ative sepsis rates of patients operated in a regular operating room versus sur- gery done in one of the newer systems uniformly showed lower rates for patients done in the newer systems. However, in none of these series was it conclusively demonstrated that the reduced airborne bacterial concentrations were the sole
7 variable associated with the lowered infection rates. It should be noted that recent papers presented at the meeting of the American Academy of Orthopaedic Surgeons in New Orleans in January 1976, reported zero infection rates without the use of "newer systems." B. Conclusions 1. A specific order of effectiveness for each system could not be ascertained at this time. 2. The Workshop participants generally agreed on the following observations and recommendations: a. Improved control of operating room personnel activity pat- terns, and impermeable drapes and garments, can signifi- cantly reduce operating room airborne bacterial concentra- tions. These principles apply in both conventional and newer system operating rooms. b. Conventional air conditioning systems should be checked frequently for filter efficiency, filter cleanliness, and room pressurization. c. Clean rooms of the HEPA filter, laminar air flow, high velocity type reduce airborne bacterial concentrations at least 80 percent when personnel wear conventional garments. Contamination is further reduced when personnel wear im- proved barrier garments. The use of helmet-aspirator- improved barrier gown systems will reduce the level of air- borne bacterial contamination at least 90 percent. The walled, vertical flow system seems to be most efficient. d. Personnel aspirator systems cannot be endorsed unequivocally because of their impracticality. However, their effective- ness in reducing shed bacteria is accepted. e. Low Velocity (25-35 ft/min) HEPA Directional Airflow Systems are considered effective in reducing operating room airborne bacterial concentrations. ⢠f. For the clean, refined, high-risk wound, supplemental pro- tection with perioperative antibiotics or air treatment systems is recommended.
Ultraviolet light is an acceptable method for reducing operating room airborne bacteria, but sufficient data are not available to justify recommending its widespread ap- aplication to operating rooms at the present time.
