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Summary There are some basic requirements for air conditioning systems in operating theatres. 1. Obviously the regulation of temperature and humidity is necessary, but cleaning of fresh air and circulating air is much more important. 2. Concerning cleaning, a high standard of filtration of air is demanded to avoid contamination of wounds. 3. So far only HEPA-filters, a technical description, give security and safety. They filter particles down to under 1 ~tm and have a filtration rate of more than 99.9~ 4. The ventilation rate is directly related to the germ concentration in the air. The higher the ventilation rate the cleaner the air during working. 5. To avoid turbulences unidirectional or uniform flow is necessary. This technique has become popular as the laminar flow technique. To get such a flow an air flow velocity of 0 45 + 0.1 m/s is necessary. 35745
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6. The arrangement of the different working places in an operating theatre is very important. Instrument tables and the operation field itself have to be in the zone of first air. 7. One of the commonest germ dispersion sources is the human body. Proper dressing and behaviour have to be observed. The airflow behind a person (in laminar cross flow) or under a person (in laminar down flow for instance when the neurosurgeon bends his head over the operating field) has to be regarded as contaminated. 8. Hygienic controls must be made in the operation theatre when unused and also under working conditions, in a sophisticated manner. If all these points are respected a real clean room technique is possible with considerable lowering of the risk of infection for the patient. Obviously all the other rules of hygiene, i.e., asepsis and antisepsis, elaborated since the days of Lister, have to be strictly respected. General Remarks Air conditioning systems have the function of regulating the tem- perature and the humidity of the air. They supply fresh air, and guarantee that supplied and circulating air is clean (Schiitz 1970). This is very important in rooms in which fine instruments or devices are produced or assembled, for instance in spacecraft technology as well as in rooms in which human or animal tissues are surgically dissected and medical or surgical treatment is applied (intensive care units, operating theatres). The following remarks are based on the knowledge of specialists. They are the result of the work of hygienists, technicians, and engineers and of discussions with those who have studied the problems of hospitalization and infection.
As a neurosurgeon I can add only a few of my own experiences to this basic knowledge. The regulation of air temperature and air humidity seems to be relatively simple compared with the requirements of clean room technique. There arise only very special and small problems like those of the operation-microscope when the eye-pieces often become fogged. With the clean room technique there are a lot of problems of technical as well as of medical or financial natures. If we speak about air conditioning systems we have to deal mainly with the problems of clean room technology. The modern hospital technology has received some very important stimuli from spacecraft technology. For the production of very fine and delicate instruments and devices it was necessary to produce and to handle them in very clean rooms (Regenscheit 1959, Whitfield 1962). For this purpose the laminar air flow technique was developed. It was assigned to medicine somewhat later when Austin and Timmer- man (1965), Charnley (1964), and Whitcomb (1969) published their first results. Allocation of severely ill patients to intensive care units and ac- cumulation of very difficult longlasting operations, sometimes in badly nourished tissues, have raised the risk of infection. The same occurs in old operating rooms in which the frequency of operations is increased. So, in recent years, a series of infections, for instance in Germany in a gynaecological hospital in Hamburg (Thomsen and Krebs 1972), led the attention of hygienists, architects, engineers, and technicians to the problems of hospital infection (Sattel and Peiper 1977, Winkler et al. 1972). Under the conditions of an operation a much higher germ contamination of the air in the operating room has been demonstrated (Botzenhart and Riiden 1973, Wanner 1972, 1974). In our own department an investigation on complications in lumbar disc operations (Schepelmann, Greiner, and Pia 1977) showed (Table 1) that 18.8~ of patients had some slight inflammation or a serious infection of the wound (in eight cases the infection was sub- fascial). In 1.5~ of the cases spondylitis complicated the disc surgery. One reason for this high incidence of infections seems to be the fact that the operation table stands in the used air zone of an over- crowded operation theatre, which was designed and built for only one operating table, and has been generally used as a two-table Table 1. Complication Rate in Lumbar-Disc-Operations as Published by F. Schepelmann, L. Greiner, and H. W. Pia Abs. %