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Reprocessing of anaesthetic and ventilatory equipment
Journal
of Hospital
Infection
Reprocessing
(1995)
30 (Supplement),
of anaesthetic equipment
414420
and ventilatory
H. K. Geiss Institute
of Hygiene and Medical Microbiology, University of Heidelberg, Im Neuenheimer Feld 324, D-69120 Heidelberg, Germany
Summary:
Uniform and standardized recommendations for reprocessing of anaesthetic and ventilatory equipment are still lacking. The uncertainty in this field is underscored by the various methods which are described in the literature which include pasteurization, immersion baths, formaldehyde cabinets, automated washers/disinfectors and sterilization procedures like autoclaving, ethylene oxide and gaseous formaldehyde. Based on the classification of anaesthetic and ventilatory equipment as semi-critical items, high level disinfection must be regarded as the appropriate decontamination procedure. In contrast to automated washers the other above-mentioned disinfection procedures lack an integrated and all inclusive reprocessing cycle which consists of cleaning, disinfection, rinsing and drying. In view of the increasing demands of employee safety, environmental suitability, costeffectiveness and quality assurance in hospital hygiene, only automated washers/disinfectors-either based on hot water disinfection or chemothermic processing-fulfil the basic requirements for safe and standardized reprocessing of anaesthetic and ventilatory equipment.
Keywords: Anaesthetic washers/disinfectors.
equipment;
ventilatory
equipment;
disinfection;
Introduction
The risk of transmitting nosocomial pathogens from one patient to another by anaesthetic equipment was first considered by Waters in 1932. In the following decades clinical studies and case reports provided additional evidence that anaesthetic and respiratory equipment may play a significant role in causing nosocomial pneumonias. Several investigators demonstrated that during mechanical ventilation face masks, Y-pieces, ventilation hoses, water traps, and breathing bags easily become contaminated by the flow of moist air expired by the patient.lm3 However, it took almost 40 years until, in the late 1960s it became generally accepted that ventilatory hoses of anaesthetic machines and equipment for long-term ventilation must be decontaminated after every patient use. The most convincing proof for the efficacy of stringent disinfection of inhalation-therapy equipment was presented by the study of Pierce and colleagues in the mid-1960s.4 They demonstrated that the introduction of daily decontamination of reservoir nebulizers with 0.25% acetic acid reduced the incidence of necrotizing 0195-6701/95/060414+07
$08.00/O
Q 1995 The Hospital
414
Infection
Society
Disinfection
of ventilatory
equipment
415
pneumonia due to Gram-negative bacilli. Nevertheless, there continues to be ongoing discussion about what constitutes adequate treatment of anaesthetic and ventilatory items. To date there are no generally accepted recommendations as to whether this equipment should be sterilized or if disinfection may be sufficient. The first published guidelines were those of the American Operating Room Nurse’s Association which recommended in 1977 that the entire anaesthetic equipment, including breathing tubes, be terminally decontaminated, cleaned and sterilized after each use. However, this recommendation is in contrast to the more rational approach to disinfection and sterilization of patient-care items and equipment which was devised by Spaulding in 1968.’ This classification scheme divides all hospital equipment into three categories based on the degree of risk of infection involved in the use of these items. According to this classification all anaesthetic and ventilatory equipment falls into the category ‘semicritical’ which means that these objects do not enter sterile tissue or the vascular system but come only into contact with mucous membranes or non-intact skin and thus only have to undergo a high-level disinfection procedure. Despite this rational approach there continues to be uncertainty over adequate reprocessing and the variety of methods applied is high-lighted by two surveys from Canada. The first study in 1984 included 38 universityaffiliated hospitals and described only ‘cleaning of anaesthesia breathing circuits and tubings’.‘j Methods used comprised disinfection with glutaraldehyde (46%), green soap, chlorhexidine + alcohol (22%), and pasteurization (32%). Pasteurization in this context is described as the use of an automatic washing machine supplied with water at 77°C for a total exposure time of 10 min. The authors finally stated that either pasteuritation or glutaraldehyde disinfection after thorough cleaning are sufficient methods for reprocessing anaesthetic equipment. A second survey was performed in 1988 comprising 21 teaching hospitals in Ontario.7 Methods that were used for treating anaesthetic equipment are summarized as follows: single use, then discarded (33%); ethylene oxide sterilization (19%); disinfection [Pasteurmatic method (33%), cidematic method (lo%), soaking in cold germicide (5%)]. Based on these data the authors proposed different approaches for dealing with anaesthetic equipment as follows:7 1. single use followed by incineration: plastic items like bain circuits, oropharyngeal airways, tracheal and nasogastric tubes, and suction catheters; 2. ethylene oxide sterilization: ventilator bellows (once weekly); 3. steam sterilization at 170°C (sic!) for 10 min: laryngoscope blades, bain valves; 4. Pasteurmatic: face masks and rubber bag after each use. Additionally, the authors stated that ‘after an infectious case, all items, including anaesthetic valves and ventilator bellows, are removed from the
H. K. Geiss
416
anaesthetic machine which is then wiped down with bleach solution’. These examples help to illustrate the lack of conclusive and rational guidelines Nevertheless, standardized refor reprocessing this kind of equipment. commendations are necessary to satisfy basic requirements of hospital infection control. Reprocessing of anaesthetic and ventilatory equipment does not differ at all from the approach to other hospital material. The basic steps of decontamination and disinfection or sterilization include: 1. preparation of the items; 2. pre-cleaning; 3. disinfection or sterilization; 4. instrument care and maintenance, storing.
Preparation
for reprocessing
All systems must be disassembled completely to allow unrestricted contact of all parts with the disinfectant. Soda-lime from the carbon dioxide absorbers must be removed completely before reprocessing of lime canisters. Measuring instruments and pressure gauges must be processed separately according to the recommendations of the manufacturers. Manual cleaning Although in a modern hospital manual cleaning should be replaced by automatic processing because there is a permanent risk of injury and infectious hazards dealing with sharp and intricate instruments, manual cleaning is still a widely used practice. Cleaning as an inherent part of the reprocessing cycle is an essential prerequisite to disinfection and sterilization. The primary purpose of cleaning is to remove organic soil which may harbour great numbers of microorganisms. The water temperature used for cleaning should not exceed 45°C because higher temperatures lead to rapid coagulation of proteinaceous soil. These aggregations may form a protective layer for microorganisms during disinfection. Plastic items with closeable hollow spaces such as breathing masks or bellows must be kept tightly closed during cleaning and disinfection to avoid inadvertent access of liquids into these cavities. Ultrasound treatment Ultrasonic baths are highly efficient in cleaning external surfaces of intricate items, particularly where blood spillage and secretions have dried onto surfaces. However, the use of ultrasonication for cleaning of materials made of plastic is unsuitable because ultrasound waves are absorbed by plastics. Also internal mechanical parts of the ventilatory systems should not be treated by ultrasonication.
Disinfection
of ventilatory
equipment
Disinfection/sterilization Disinfection For disinfection of anaesthetic methods are described.
and ventilator
417
methods
equipment
four different
1. Soaking in germicides. A widely used practice which is often called ‘cold sterilization’ is the immersion of the different items in solutions containing disinfectants with varying concentrations. In most cases these disinfectants consist of aldehydes which per seexhibit a very good germicidal activity depending on use concentration and the duration of exposure or contact time. Thus, first of all, aldehyde-based immersion baths seem to be foolproof due to their obviously simple performance, material compatibility, and the fact that items can be processed on the spot. However, this method has a relatively high failure rate. Besides possible dosing errors and insufficient contact time, major disadvantages are toxicity, skin irritation and allergy as well as environmental concerns with all aldehydes. Gloves must be worn, immersion basins covered and the disinfectant stored and used away from busy areas. Fume cupboards or exhaust ventilation may be necessary to remove toxic vapours. Another typical failure is inadequate disinfection by insufficient contact with the disinfectant due to air trapping.’ All inner and outer surfaces must be in contact with the disinfectant. After the predetermined exposure time all items must be rinsed thoroughly to remove the remaining disinfectant. Using tap water may lead to recontamination which is critical if the items are not dried adequately. Weighing up all pros and cons of this disinfection method, negative aspects predominate and argue strongly against the widespread use of immersion baths in hospitals. 2. Formaldehye chambers. Another method, even far more outdated than immersion baths, employs formaldehyde chambers or cabinets. Their intended use is primarily to disinfect bulky items like anaesthetic machines, ventilators and incubators. However, the latter should not be treated in formaldehyde cabinets since it has been shown that residual formaldehyde concentrations in incubators reach toxic levels. Although vaporized formaldehyde is highly germicidal it is only effective on clean exposed surfaces. Items are preheated to approximately 40°C under defined humidity. Methanolized formalin is heated until formaldehyde vapour is generated which is then circulated through the chamber. After a cycle time of 3-6 h residual formaldehyde is neutralized with ammonia and the chamber is finally flushed with air. Even if, in comparison to immersion disinfection, process parameters are standardized, formaldehyde cabinets by and large can be regarded as unnecessary because there are safer alternatives to the use of gaseous formaldehyde for disinfection purposes.
418
H.
K. Geiss
While in French and German-speaking countries the 3. Pasteurization. term pasteurization is used only in connection with the preservation of food, English and American literature defines this process as using hot water at 77°C for 30 min to destroy all pathogenic microorganisms except bacterial spores.’ It is regarded as an alternative to chemical disinfection of respiratory therapy and anaesthetic equipment. As cleaning is not part and most process parameters are too of the decontamination process, variable, the use of pasteurizers is increasingly being discouraged in hospitals.” 4. Automated machine-based disinfection. A common feature of all above mentioned disinfection methods is that they lack a standardized procedure and that all items treated by either method must be pre-cleaned manually to ensure safe and complete removal of infecting organisms during the disinfection cycle. Therefore, the use of automated washers/disinfectors should be preferred over manual reprocessing because pre-cleaning, disinfection, rinsing and drying are performed during a single process cycle without repeated direct contact and manipulation by the staff. Originally deriving from household dishwashers these machines are nowadays highly specialized and automatic being equipped with microprocessor control systems which guarantee a standardized and reliable processing of all types of hospital equipment. They are offered in different sizes and in various models like single front door machines, pass-through machines, or as compartmentalized tunnel washers to meet all demands of the user. They are equipped with several rotary spray arms, jet sprays and racks containing spray nozzles which can hold lumened devices. Most units automatically process through a number of pre-wash, disinfection, rinse and drying cycles. The load is commonly rinsed in cool or tepid water to prevent organic soil from baking on before water temperature is increased to wash temperature. Automated measured dosing pumps add cleaning, disinfecting, neutralizing agents and even instrument milk. Drying is performed by high pressure hot air blowers which use sterile filtered fresh air. Different wire mesh stainless steel baskets and racks are available which enable processing of any kind of equipment. One of the newer machines is even fitted with a specific cleaning system for breathing bags. The special design of this jet nozzle enables rinsing and drying of the complete inner surface of these breathing bags. Two different types of disinfection are used: either applying only hot water at a temperature of 90°C for a holding time of 10 min, or chemothermic processing, i.e. the use of an aldehyde-based disinfectant at lower temperatures of about 60°C. Although the lower temperature has advantages concerning material compatibility there is some environmental uneasiness about the use of chemicals for disinfection. Furthermore, the success of chemothermic disinfection relies mainly on the design of the water spraying system, i.e.
Disinfection
of ventilatory
equipment
419
the ability of the disinfecting solution to have thorough contact with all inner and outer surfaces of the objects to be disinfected, which sometimes may be difficult and may be the reason for inadequate disinfection. Heat stress and related material damage in pure thermic processing can be avoided if the water temperature rises gradually, excluding sudden temperature changes, especially when hot air drying is performed. Thus hot water washers seem to have some advantages over chemothermic washers/disinfectors. Sterilization As mentioned above, sterilization of anaesthetic and ventilatory equipment is generally unnecessary. This is demonstrated by several studies which failed to show a lower infection rate if ventilatory equipment is sterilized in comparison to items which are only high-level disinfected.“-” However, if this equipment is sterilized for whatever reason, again steam is the preferred method. Using ethylene oxide or formaldehyde may pose significant toxicity problems as described in the literature.i%is If conventional autoclaving is used the following points should be kept in mind. 1. Plastic items with or without bags made of silicone elastomeres or natural rubber can be treated by steam sterilization. Due to the shorter exposure time a temperature of 134°C is preferred. Items made of thermoplastic materials should be steam sterilized only when this method is certified by the manufacturer. 2. During autoclaving of plastic items hollow spaces must be kept open to avoid damage by pressure changes. Holloware with valves must be free of water and air during sterilization, 3. Functional parts of the ventilatory systems can also be sterilized using a maximum temperature of 134°C. 4. The use of heat sterilization at 180°C cannot be applied to ventilatory equipment because excessive heat will irreversibly damage all items containing rubber elastomere parts. Conclusion
Reprocessing of anaesthetic and ventilatory equipment, despite the variety of technically different items, should pose no more major problems in hospitals. In view of the progress in machine technology during the last few years reprocessing of this equipment using either hot water washers or washers/disinfectors has become a very simple, reliable, economically and ecologically acceptable method which fulfils basic requirements of hospital infection control. Although these machines are quite expensive, the use of more and more delicate and intricate instruments, not only in the field of ventilatory equipment, but especially in minimal invasive surgery, necessitates a standardized and safe processing cycle. Additionally,
H.
420
Geiss
K.
issues of employee health argue strongly in favour of automated processing. We should all be concerned about infection prevention in patients but also about improving safety standards for health care workers who deal with contaminated patient-care items. References 1. Bonath
K, Geiss Langzeitbeatmung. 185. 2. Heeg P, Daschner
HK,
Jiirs
G,
Krier
Aniisthesiologie, F. Bacteriological
C.
Kontamination
Intensivmedizin investigations
von
Beatmungsgeraten
bei
und Notfallmedizin
1989; 24: 181-
on used
machines.
anesthesia
Hyg
Med 1986; 11: 470-472. 3. Malecka-Griggs B, Kennedy C, Ross B. Microbial burden in disposable and nondisposable ventilator circuits used for 24 and 48 h in intensive care units. J Clin Microbial 1989; 27: 495-503. 4. Pierce AK, Sanford JP, Thomas GD, Leonard JS. Long-term evaluation of decontamination of inhalation-therapy equipment and the occurrence of necrotizing pneumonia. N Engl r Med 1970; 282: 528-531. 5. Spaulding EH. Chemical disinfection of medical and surgical materials. In: Lawrence CA, Block SS, Eds. Disinfection, Sterilization and Preservation. Philadelphia: Lea & Febiger 1968; 517-531. 6. Barry AE, Noble MA, Marrie TJ, Paterson IJ. Cleaning of anaesthetic breathing circuits and tubings: a Canadian survey. Can Anaesthesiol Sot J 1984; 31: 572-575. 7. Brown RA, Bell R, Pine W, Bosnjak T. Sterilization of anaesthetic equipment. Can J Anaesthesia 1989; 36: 359-361. 8. Im SWK, Fung JPH, Yu DYC. Unusual dissemination of pseudomonads by ventilators. Anaesthesia 1982; 37: 1074-1077. 9. Rutala RW. Disinfection, sterilization and waste disposal. In: Wenzel RP, Ed. Prevention and Control of Nosocomial Infections. Baltimore: Williams & Wilkins 1993; 460-496. 10. Babb JR. Methods of cleaning and disinfection. Zentralsterilisation Central Service 1993; 1: 227-237. 11. Du Moulin CG, Saubermann AJ. The anaesthesia machine and circle system are not likely to be sources of bacterial contamination. Anesthesiology 1979; 47: 353-358. 12. Feeley TW, Hamilton WK, Xavier B, Moyers J, Eger EI. Sterile anesthesia breathing circuits do not prevent postoperative pulmonary infection. Anesthesiology 1981; 54: 369-372. 13. Belani KG, Priedkalns J. An epidemic of pseudomembranous laryngotracheitis. Anesthesiology 1977: 47: 530-531. Lawler PG. Inhalation of formaldehyde vapour. Anaesthesia 1980; 37: 1102-1103. Lipton B, Gutierrez R, Blaugrund S, Litwak RS, Rendell-Baker L. Irradiated PVC plastic and gas sterilization in the production of tracheal stenosis following tracheostomy.
Anesthes Analges 1971; 50: 578-586.
of Hospital
Infection
Reprocessing
(1995)
30 (Supplement),
of anaesthetic equipment
414420
and ventilatory
H. K. Geiss Institute
of Hygiene and Medical Microbiology, University of Heidelberg, Im Neuenheimer Feld 324, D-69120 Heidelberg, Germany
Summary:
Uniform and standardized recommendations for reprocessing of anaesthetic and ventilatory equipment are still lacking. The uncertainty in this field is underscored by the various methods which are described in the literature which include pasteurization, immersion baths, formaldehyde cabinets, automated washers/disinfectors and sterilization procedures like autoclaving, ethylene oxide and gaseous formaldehyde. Based on the classification of anaesthetic and ventilatory equipment as semi-critical items, high level disinfection must be regarded as the appropriate decontamination procedure. In contrast to automated washers the other above-mentioned disinfection procedures lack an integrated and all inclusive reprocessing cycle which consists of cleaning, disinfection, rinsing and drying. In view of the increasing demands of employee safety, environmental suitability, costeffectiveness and quality assurance in hospital hygiene, only automated washers/disinfectors-either based on hot water disinfection or chemothermic processing-fulfil the basic requirements for safe and standardized reprocessing of anaesthetic and ventilatory equipment.
Keywords: Anaesthetic washers/disinfectors.
equipment;
ventilatory
equipment;
disinfection;
Introduction
The risk of transmitting nosocomial pathogens from one patient to another by anaesthetic equipment was first considered by Waters in 1932. In the following decades clinical studies and case reports provided additional evidence that anaesthetic and respiratory equipment may play a significant role in causing nosocomial pneumonias. Several investigators demonstrated that during mechanical ventilation face masks, Y-pieces, ventilation hoses, water traps, and breathing bags easily become contaminated by the flow of moist air expired by the patient.lm3 However, it took almost 40 years until, in the late 1960s it became generally accepted that ventilatory hoses of anaesthetic machines and equipment for long-term ventilation must be decontaminated after every patient use. The most convincing proof for the efficacy of stringent disinfection of inhalation-therapy equipment was presented by the study of Pierce and colleagues in the mid-1960s.4 They demonstrated that the introduction of daily decontamination of reservoir nebulizers with 0.25% acetic acid reduced the incidence of necrotizing 0195-6701/95/060414+07
$08.00/O
Q 1995 The Hospital
414
Infection
Society
Disinfection
of ventilatory
equipment
415
pneumonia due to Gram-negative bacilli. Nevertheless, there continues to be ongoing discussion about what constitutes adequate treatment of anaesthetic and ventilatory items. To date there are no generally accepted recommendations as to whether this equipment should be sterilized or if disinfection may be sufficient. The first published guidelines were those of the American Operating Room Nurse’s Association which recommended in 1977 that the entire anaesthetic equipment, including breathing tubes, be terminally decontaminated, cleaned and sterilized after each use. However, this recommendation is in contrast to the more rational approach to disinfection and sterilization of patient-care items and equipment which was devised by Spaulding in 1968.’ This classification scheme divides all hospital equipment into three categories based on the degree of risk of infection involved in the use of these items. According to this classification all anaesthetic and ventilatory equipment falls into the category ‘semicritical’ which means that these objects do not enter sterile tissue or the vascular system but come only into contact with mucous membranes or non-intact skin and thus only have to undergo a high-level disinfection procedure. Despite this rational approach there continues to be uncertainty over adequate reprocessing and the variety of methods applied is high-lighted by two surveys from Canada. The first study in 1984 included 38 universityaffiliated hospitals and described only ‘cleaning of anaesthesia breathing circuits and tubings’.‘j Methods used comprised disinfection with glutaraldehyde (46%), green soap, chlorhexidine + alcohol (22%), and pasteurization (32%). Pasteurization in this context is described as the use of an automatic washing machine supplied with water at 77°C for a total exposure time of 10 min. The authors finally stated that either pasteuritation or glutaraldehyde disinfection after thorough cleaning are sufficient methods for reprocessing anaesthetic equipment. A second survey was performed in 1988 comprising 21 teaching hospitals in Ontario.7 Methods that were used for treating anaesthetic equipment are summarized as follows: single use, then discarded (33%); ethylene oxide sterilization (19%); disinfection [Pasteurmatic method (33%), cidematic method (lo%), soaking in cold germicide (5%)]. Based on these data the authors proposed different approaches for dealing with anaesthetic equipment as follows:7 1. single use followed by incineration: plastic items like bain circuits, oropharyngeal airways, tracheal and nasogastric tubes, and suction catheters; 2. ethylene oxide sterilization: ventilator bellows (once weekly); 3. steam sterilization at 170°C (sic!) for 10 min: laryngoscope blades, bain valves; 4. Pasteurmatic: face masks and rubber bag after each use. Additionally, the authors stated that ‘after an infectious case, all items, including anaesthetic valves and ventilator bellows, are removed from the
H. K. Geiss
416
anaesthetic machine which is then wiped down with bleach solution’. These examples help to illustrate the lack of conclusive and rational guidelines Nevertheless, standardized refor reprocessing this kind of equipment. commendations are necessary to satisfy basic requirements of hospital infection control. Reprocessing of anaesthetic and ventilatory equipment does not differ at all from the approach to other hospital material. The basic steps of decontamination and disinfection or sterilization include: 1. preparation of the items; 2. pre-cleaning; 3. disinfection or sterilization; 4. instrument care and maintenance, storing.
Preparation
for reprocessing
All systems must be disassembled completely to allow unrestricted contact of all parts with the disinfectant. Soda-lime from the carbon dioxide absorbers must be removed completely before reprocessing of lime canisters. Measuring instruments and pressure gauges must be processed separately according to the recommendations of the manufacturers. Manual cleaning Although in a modern hospital manual cleaning should be replaced by automatic processing because there is a permanent risk of injury and infectious hazards dealing with sharp and intricate instruments, manual cleaning is still a widely used practice. Cleaning as an inherent part of the reprocessing cycle is an essential prerequisite to disinfection and sterilization. The primary purpose of cleaning is to remove organic soil which may harbour great numbers of microorganisms. The water temperature used for cleaning should not exceed 45°C because higher temperatures lead to rapid coagulation of proteinaceous soil. These aggregations may form a protective layer for microorganisms during disinfection. Plastic items with closeable hollow spaces such as breathing masks or bellows must be kept tightly closed during cleaning and disinfection to avoid inadvertent access of liquids into these cavities. Ultrasound treatment Ultrasonic baths are highly efficient in cleaning external surfaces of intricate items, particularly where blood spillage and secretions have dried onto surfaces. However, the use of ultrasonication for cleaning of materials made of plastic is unsuitable because ultrasound waves are absorbed by plastics. Also internal mechanical parts of the ventilatory systems should not be treated by ultrasonication.
Disinfection
of ventilatory
equipment
Disinfection/sterilization Disinfection For disinfection of anaesthetic methods are described.
and ventilator
417
methods
equipment
four different
1. Soaking in germicides. A widely used practice which is often called ‘cold sterilization’ is the immersion of the different items in solutions containing disinfectants with varying concentrations. In most cases these disinfectants consist of aldehydes which per seexhibit a very good germicidal activity depending on use concentration and the duration of exposure or contact time. Thus, first of all, aldehyde-based immersion baths seem to be foolproof due to their obviously simple performance, material compatibility, and the fact that items can be processed on the spot. However, this method has a relatively high failure rate. Besides possible dosing errors and insufficient contact time, major disadvantages are toxicity, skin irritation and allergy as well as environmental concerns with all aldehydes. Gloves must be worn, immersion basins covered and the disinfectant stored and used away from busy areas. Fume cupboards or exhaust ventilation may be necessary to remove toxic vapours. Another typical failure is inadequate disinfection by insufficient contact with the disinfectant due to air trapping.’ All inner and outer surfaces must be in contact with the disinfectant. After the predetermined exposure time all items must be rinsed thoroughly to remove the remaining disinfectant. Using tap water may lead to recontamination which is critical if the items are not dried adequately. Weighing up all pros and cons of this disinfection method, negative aspects predominate and argue strongly against the widespread use of immersion baths in hospitals. 2. Formaldehye chambers. Another method, even far more outdated than immersion baths, employs formaldehyde chambers or cabinets. Their intended use is primarily to disinfect bulky items like anaesthetic machines, ventilators and incubators. However, the latter should not be treated in formaldehyde cabinets since it has been shown that residual formaldehyde concentrations in incubators reach toxic levels. Although vaporized formaldehyde is highly germicidal it is only effective on clean exposed surfaces. Items are preheated to approximately 40°C under defined humidity. Methanolized formalin is heated until formaldehyde vapour is generated which is then circulated through the chamber. After a cycle time of 3-6 h residual formaldehyde is neutralized with ammonia and the chamber is finally flushed with air. Even if, in comparison to immersion disinfection, process parameters are standardized, formaldehyde cabinets by and large can be regarded as unnecessary because there are safer alternatives to the use of gaseous formaldehyde for disinfection purposes.
418
H.
K. Geiss
While in French and German-speaking countries the 3. Pasteurization. term pasteurization is used only in connection with the preservation of food, English and American literature defines this process as using hot water at 77°C for 30 min to destroy all pathogenic microorganisms except bacterial spores.’ It is regarded as an alternative to chemical disinfection of respiratory therapy and anaesthetic equipment. As cleaning is not part and most process parameters are too of the decontamination process, variable, the use of pasteurizers is increasingly being discouraged in hospitals.” 4. Automated machine-based disinfection. A common feature of all above mentioned disinfection methods is that they lack a standardized procedure and that all items treated by either method must be pre-cleaned manually to ensure safe and complete removal of infecting organisms during the disinfection cycle. Therefore, the use of automated washers/disinfectors should be preferred over manual reprocessing because pre-cleaning, disinfection, rinsing and drying are performed during a single process cycle without repeated direct contact and manipulation by the staff. Originally deriving from household dishwashers these machines are nowadays highly specialized and automatic being equipped with microprocessor control systems which guarantee a standardized and reliable processing of all types of hospital equipment. They are offered in different sizes and in various models like single front door machines, pass-through machines, or as compartmentalized tunnel washers to meet all demands of the user. They are equipped with several rotary spray arms, jet sprays and racks containing spray nozzles which can hold lumened devices. Most units automatically process through a number of pre-wash, disinfection, rinse and drying cycles. The load is commonly rinsed in cool or tepid water to prevent organic soil from baking on before water temperature is increased to wash temperature. Automated measured dosing pumps add cleaning, disinfecting, neutralizing agents and even instrument milk. Drying is performed by high pressure hot air blowers which use sterile filtered fresh air. Different wire mesh stainless steel baskets and racks are available which enable processing of any kind of equipment. One of the newer machines is even fitted with a specific cleaning system for breathing bags. The special design of this jet nozzle enables rinsing and drying of the complete inner surface of these breathing bags. Two different types of disinfection are used: either applying only hot water at a temperature of 90°C for a holding time of 10 min, or chemothermic processing, i.e. the use of an aldehyde-based disinfectant at lower temperatures of about 60°C. Although the lower temperature has advantages concerning material compatibility there is some environmental uneasiness about the use of chemicals for disinfection. Furthermore, the success of chemothermic disinfection relies mainly on the design of the water spraying system, i.e.
Disinfection
of ventilatory
equipment
419
the ability of the disinfecting solution to have thorough contact with all inner and outer surfaces of the objects to be disinfected, which sometimes may be difficult and may be the reason for inadequate disinfection. Heat stress and related material damage in pure thermic processing can be avoided if the water temperature rises gradually, excluding sudden temperature changes, especially when hot air drying is performed. Thus hot water washers seem to have some advantages over chemothermic washers/disinfectors. Sterilization As mentioned above, sterilization of anaesthetic and ventilatory equipment is generally unnecessary. This is demonstrated by several studies which failed to show a lower infection rate if ventilatory equipment is sterilized in comparison to items which are only high-level disinfected.“-” However, if this equipment is sterilized for whatever reason, again steam is the preferred method. Using ethylene oxide or formaldehyde may pose significant toxicity problems as described in the literature.i%is If conventional autoclaving is used the following points should be kept in mind. 1. Plastic items with or without bags made of silicone elastomeres or natural rubber can be treated by steam sterilization. Due to the shorter exposure time a temperature of 134°C is preferred. Items made of thermoplastic materials should be steam sterilized only when this method is certified by the manufacturer. 2. During autoclaving of plastic items hollow spaces must be kept open to avoid damage by pressure changes. Holloware with valves must be free of water and air during sterilization, 3. Functional parts of the ventilatory systems can also be sterilized using a maximum temperature of 134°C. 4. The use of heat sterilization at 180°C cannot be applied to ventilatory equipment because excessive heat will irreversibly damage all items containing rubber elastomere parts. Conclusion
Reprocessing of anaesthetic and ventilatory equipment, despite the variety of technically different items, should pose no more major problems in hospitals. In view of the progress in machine technology during the last few years reprocessing of this equipment using either hot water washers or washers/disinfectors has become a very simple, reliable, economically and ecologically acceptable method which fulfils basic requirements of hospital infection control. Although these machines are quite expensive, the use of more and more delicate and intricate instruments, not only in the field of ventilatory equipment, but especially in minimal invasive surgery, necessitates a standardized and safe processing cycle. Additionally,
H.
420
Geiss
K.
issues of employee health argue strongly in favour of automated processing. We should all be concerned about infection prevention in patients but also about improving safety standards for health care workers who deal with contaminated patient-care items. References 1. Bonath
K, Geiss Langzeitbeatmung. 185. 2. Heeg P, Daschner
HK,
Jiirs
G,
Krier
Aniisthesiologie, F. Bacteriological
C.
Kontamination
Intensivmedizin investigations
von
Beatmungsgeraten
bei
und Notfallmedizin
1989; 24: 181-
on used
machines.
anesthesia
Hyg
Med 1986; 11: 470-472. 3. Malecka-Griggs B, Kennedy C, Ross B. Microbial burden in disposable and nondisposable ventilator circuits used for 24 and 48 h in intensive care units. J Clin Microbial 1989; 27: 495-503. 4. Pierce AK, Sanford JP, Thomas GD, Leonard JS. Long-term evaluation of decontamination of inhalation-therapy equipment and the occurrence of necrotizing pneumonia. N Engl r Med 1970; 282: 528-531. 5. Spaulding EH. Chemical disinfection of medical and surgical materials. In: Lawrence CA, Block SS, Eds. Disinfection, Sterilization and Preservation. Philadelphia: Lea & Febiger 1968; 517-531. 6. Barry AE, Noble MA, Marrie TJ, Paterson IJ. Cleaning of anaesthetic breathing circuits and tubings: a Canadian survey. Can Anaesthesiol Sot J 1984; 31: 572-575. 7. Brown RA, Bell R, Pine W, Bosnjak T. Sterilization of anaesthetic equipment. Can J Anaesthesia 1989; 36: 359-361. 8. Im SWK, Fung JPH, Yu DYC. Unusual dissemination of pseudomonads by ventilators. Anaesthesia 1982; 37: 1074-1077. 9. Rutala RW. Disinfection, sterilization and waste disposal. In: Wenzel RP, Ed. Prevention and Control of Nosocomial Infections. Baltimore: Williams & Wilkins 1993; 460-496. 10. Babb JR. Methods of cleaning and disinfection. Zentralsterilisation Central Service 1993; 1: 227-237. 11. Du Moulin CG, Saubermann AJ. The anaesthesia machine and circle system are not likely to be sources of bacterial contamination. Anesthesiology 1979; 47: 353-358. 12. Feeley TW, Hamilton WK, Xavier B, Moyers J, Eger EI. Sterile anesthesia breathing circuits do not prevent postoperative pulmonary infection. Anesthesiology 1981; 54: 369-372. 13. Belani KG, Priedkalns J. An epidemic of pseudomembranous laryngotracheitis. Anesthesiology 1977: 47: 530-531. Lawler PG. Inhalation of formaldehyde vapour. Anaesthesia 1980; 37: 1102-1103. Lipton B, Gutierrez R, Blaugrund S, Litwak RS, Rendell-Baker L. Irradiated PVC plastic and gas sterilization in the production of tracheal stenosis following tracheostomy.
Anesthes Analges 1971; 50: 578-586.