Document O1rbo13rReYnj6JoOZkVZrzoL

222 CHAPTER 13 1948 Guide , cyclopropane, one of the best but most difficult gases to handle. The use of helium as a diluent in the total gaseous mixture controls the oxygen concentration by displacement and, because of its flame quenching proper ties, it is the ideal gas for this purpose. In addition,.a gaseous mixture containing helium is more difficult to ignite by electric discharges and this quality also increases the safety factor of anesthetic administration. Operating Room Conditions Little is known about 'optimum air conditions for maintaining normal body temperatures during anesthesia and the immediate post-operative period.. An anesthetized patient displays dilation of blood vessels in the skin resulting in profuse sweating and (it has been believed) inability to regulate body temperature. From this it was concluded that all anesthetized patients suffered considerable heat loss, although there may be iittle more than 0.8 F Variation in the rectal temperature during the course of the operation16. The severe physiological effects, such as excessive sweating and rapid pulse, of high operating room temperatures on attendants and patients during the hot months signify the need for proper cooling. A comparison of surgeons' statements who operate in both air conditioned and non-air conditioned rooms strongly indicates that the recuperative power of the patient is greater when operated upon in air conditioned rooms18. Although the comfortable air conditions for the operators are not identical with those for the patient, it is usually not difficult to compro mise within a range of 55 to 60 per cent relative humidity and 72 to 80 F temperature. The work just cited reported that 68 to 70 F effective temperature not only furnished comfort for the operating room workers, but apparently prevented exhaustion of the patient as evidenced by rapid convalescence in the recovery ward. Additional heat may be furnished to the patient locally or by suitable covering according to body tempera ture in individual cases. In the control of airborne infection in the operating room the prevention of dispersal of infectious materials into the air, control of dust and proper ventilation supersede attempts to remove or kill pathogenic organisms. The bacterial content of conditioned operating rooms is generally lower than that of non-conditioned rooms. Bacterial counts aboard an air conditioned submarine were found to be exceptionally low and not cumulative with time although all of the air was recirculated for more than 12 hours17 without replenishment. The removal of bacteria by the process of air cooling and condensation of moisture out of air merits further study18. The degree of air contamination can be reduced by proper ventilation if velocity of air over the floor does not exceed 50 fpm. Research is in progress on the use of filtered air flowing through a system of mechanical cleaners which protect the patient against infection from attendants and from bacteria-containing air in the corridor or ward 1S. Operations may be postponed on allergic patients during asthmatic manifestations through fear of complications. The removal of air-borne allergens, therefore, is in some cases an important function of the air conditioning system in preparing patients for operation. Central system air conditioning plants and unit air conditioners prove satisfactory in operating rooms when producing between 8 and' 12 air changes per hour of filtered and properly conditioned air without recircu lation during .the course of anesthesia. A separate exhaust fan system is Air Conditioning in the Prevention and Treatment of Disease -------------------- ^-------------------------------- ----------------------------------------- ---------------- --- :-- 223 usually necessary to confine and remove the gases and odors. Double windows are desirable and often necessary to prevent condensation and frosting on the glass in cold weather and to minimize drafts. The air flow of 8 to 12 air changes in operating rooms should: (1) reduce the concen tration of the anesthetic to well below the pharmacologic threshold in the vicinity of the operating personnel, (2) remove the great amounts of heat and sometimes moisture, from sterilizing equipment if inside the operating room, from the powerful surgical lights, from solar heat, andfrom the bodies of the operatives, and (3) provide extra capacity for quickly preparing the room for emergency operations. Much can be gained by thermal insulation of sterilizing equipment and by thorough exhaust ventilation of sterilizing rooms adjoining the operating rooms. Too great a difference in temperature between the operating room and the final hospital destination of the patient, including corridors and elevators, is conducive to infections of the upper part of the respiratory tract and post-operative pneumonia. A suggested remedy is a recovery ward in which conditions closely approximate those of the operating room and in which the patients remain from one to four days. Satis factory conditions in the recovery ward not only hasten convalescence, but dispel the fear frequently found in patients who must undergo operations during the hot seasons. Experience has shown that a few hours after the operation the tem perature of the post-operative room can be decreased a few degrees below that of an overheated operating room to stimulate recovery. NURSERIES FOR PREMATURE INFANTS One of the most important requirements in the care of premature infants is the stabilization of body temperature. This is necessary because their heat regulating systems are not fully developed; the metabolism is low and the infants generally exhibit marked inability to maintain normal body temperatures. The resistance to infection is low and mortality rate high. Air Conditioning Requirements The optimum air conditions for growth and development of premature infants were determined by extensive research20 at the Children's Hospital, Boston, Mass., using four valid criteria, namely, stability of. body tem perature, gain in weight, incidence of digestive syndromes, and mortality. Individual temperature requirements varied widely (from 72 to 100 F) according to the constitutional state of the infants and body weights. The optimum relative humidity was about 65 per cent, and the air movement less than 20 fpm. A single nursery conditioned to 77 F and 65 per cent relative humidity was found to fulfill satisfactorily the requirements of the majority of premature infants. Additional heat for weak (or debilitated) infants may be furnished in the cribs or by means of electric incubators placed inside the conditioned nursery, and the temperature adjusted according to individual requirements. In this way multiplicity of chambers and of air conditioning apparatus is obviated; the infants in the heated beds derive the benefit of breathing cool humid air, and the nurses and doctors need not expose themselves to extreme conditions. Importance of Humidity: Although external heat is an important factor in the maintenance of normal body temperature, humidity appears