Evaluation of the draeger anaesthetic equipment washing machine (ANDA 9002)

rournal

of Hospital

Infection

(1989)

13, 399411

EQUIPMENT

Evaluation

REPORT

of the Draeger Washing Machine

R. S. Miles,

R. Wolfe,

Anaesthetic Equipment (ANDA 9002)

IN. Malcolm-Smith*

and G. Bowick’f

Department of Bacteriology, University of Edinburgh, *Department of Anaesthetics, and 7 Works Department, Royal Injirmary of Edinburgh, Edinburgh, UK Summary: An evaluation was made of an anaesthetic equipment washing machine. Our results largely substantiated the manufacturers claims. A clean, dry, disinfected load could be produced within 75 min. After minor modifications were made to the machine by the manufacturers, potential users were satisfied with its performance. We recommend consideration of this type of equipment for use in hospitals. Keywords:

Anaesthetic

equipment;

washer/disinfectors.

Introduction Many hospitals clean and reprocess a wide range of equipment in washing machines. Such machines are usually expected to disinfect the load during either the washing and rinsing or drying cycles and it is generally agreed that heat is the most satisfactory disinfecting agent. The process is controllable, often automated and avoids the use of potentially toxic chemical agents. Choosing a satisfactory machine, one that is suitable for a particular function, is a difficult task. Until recently, methods of measuring the cleaning and disinfecting efhciency of machines did not agree and few possessed the necessary expertise to make these assessments. Fortunately, some guidelines are now available (Collins et al., 1986), although these refer to bedpan washers. Microbiologists, when assessing machines, must still satisfy themselves that the cleaning and disinfection performance is satisfactory. Further, engineers and users of the processed equipment must also be satisfied with machine performance. It has been generally accepted for some years that anaesthetic equipment and breathing circuits should be clean and free from contamination with Correspondence Teviot Place,

019556701/89/040399+

to: R. S. Miles, Edinburgh EH8

Department 9AG, UK

of Bacteriology,

II s03.00/0

University

of Edinburgh

Medical

0 1989 The Hospnal

399

Infemon

School,

Socey

400

R. S. Miles

et

al.

potential respiratory pathogens (Lumley, 1976). There is, however, no firm evidence that the provision of sterile, rather than simply clean anaesthetic circuits, will reduce infection (Feeley et al., 1980). In November 1985, Hospital Planning Note 7, [Scottish Home and Health Department (SHHD), 19851, which add ressed the problems associated with the cleaning and disinfection of patient connected medical equipment, was issued to the Scottish Health Service. The note recommends the use of low-temperature steam with or without formaldehyde for the decontamination of heat sensitive items such as anaesthetic equipment. Draeger Medical Ltd, in collaboration with Miele of West Germany, have manufactured a cabinet washing machine which they claim can wash, disinfect and dry anaesthetic equipment. This paper reports on the evaluation of the Draeger Anaesthetic Equipment Washing Machine (ANDA 9002). Materials

and

methods

The ANDA 9002 is a fixed-location, front-loading machine with an exterior and chamber constructed of stainless steel. The machine is designed with two electrically interlocked doors and the version tested included a built-in drying unit with a steam and hot-air condenser. A water softener is incorporated into the machine and dispenser units for washing powder, rinsing and antifoaming agents are provided. The load configuration in the machine is shown in Figure 1 and diagrammatically in Figure 2. Individual items used as a test load were as follows. On the upper manifold: Ll-4.5 uncuffed red rubber endotracheal tube; L2--8.5 latex armoured endotracheal tube; L3-black rubber catheter mount and fitting; L4-8.5 cuffed red rubber endotracheal tube; LS-size 2 airway; L6-9.5 cuffed red rubber endotracheal tube; L8-6.0 cuffed Oxford red rubber endotracheal tube; L9--5.5 latex armoured cuffed endotracheal tube; LlO-catheter mount + Portex connector; Rl -Size 2 black rubber airway; R2-9.5 red rubber cuffed endotracheal tube; R3-9.5 red rubber cuffed endotracheal tube; R4-Size 4 plastic airway; R5Catheter mount; R6-10.0 cuffed red rubber endotracheal tube; R7-Size 4 plastic airway; R8--10.0 cuffed Oxford red rubber endotracheal tube; R99.5 red rubber cuffed endotracheal tube; RlO-9.5 red rubber cuffed endotracheal tube. On the lower manifold: Bl-1.1 m black rubber respiratory hose; B21.1 m black rubber respiratory hose; B3-latex (non-disposable) Bennett & Siemans respiratory hose; B4-1.1 m black rubber respiratory hose; B51.1 m black rubber respiratory hose; B6-latex (non disposable) Bennett & Siemans respiratory hose; B7-Bain circuit (disposable); BS-1.1 m black rubber respiratory hose; B9-1.1 m black rubber respiratory hose; BlO1 m Vygon disposable hose; F1 -soda lime canister; F2-soda lime canister;

Anaesthetic

Figure

1. The

ANDA

equipment

9002

washing

anaesthetic

equipment

machine

washing

401

machine.

Ll L2 L3 L4 L5 LS

Upper

Figure 2. Diagrammatic short horizontal jets with is an open mesh shelf.

manifold

representation holding clips,

of manifolds Bl-10 curved

viewed from above. Ll-10 and Rl-10 spray jets, Fl&8 vertical jets, Tray area

402

R. S. Miles

et al.

F3-4 litre reservoir bag; F4-4 litre reservoir bag; FS-2 litre reservoir bag; F6-2 litre reservoir bag; F7-4 litre reservoir bag; F8-4 litre reservoir bag. On the tray: Soda lime canister top, 3 black rubber face masks (Leyland, Warne and Rendall Baker types), 1 airway, 1 Ambu face mask, 1 child’s facemask, 1 laryngoscope blade and bulb, 2 McGill suction unions, 1 childs airway (size 0), Heidbrink valve block, 1 childs Water’s canister (in 3 sections), Black rubber bung, Ohmeda Mark 4a CO, absorber (disassembled). Other configurations are available from the manufacturer. The load insert is of a roll-in, roll-out design. Tests of heat distribution Items washed in the ANDA 9002 are exposed to washing temperatures above 70°C on two occasions during the cycle. The machine controls allow for independent variation of these two peaks of temperature (Tl, the wash cycle and T2, the rinse cycle). The duration of exposure to these temperatures is determined by use of a pre-punched plastic-control-card system. The system allows for variation of Tl and T2 between 70°C and 95°C for any desired length of time. A dial on the control panel allows presetting of the drying time. The drying temperature is set by the manufacturers at 90°C. Temperatures were recorded using a Honeywell twelve-pen thermocouple recorder. Thermocouples were taped in position at one of the following groups of sites: Group A: L6-at the centre of the endotracheal tube, B7-at the distal (furthest from manifold) end of the Bain circuit, F4-inside the reservoir bag, Tray-inside the body of a Leyland face mask, BS-at the proximal (nearest manifold) end of the black rubber respiratory hose, to the wall adjacent to the machine (ambient temperature) and cemented in position in the final water inlet to the machine. Group B: load insert-water inlet, load insert-air inlet, Rl-at the centre of black rubber airway, FE&inside the reservoir bag, free in chamber, fixed to outside of door and in the hot water supply. Group C: B8-at the proximal end of the black rubber respiratory hose, B8-at the centre of the black rubber respiratory hose, BS-at the distal end of the black rubber respiratory hose, F7-inside the reservoir bag, F7-outside surface of reservoir bag, LlO-inside Portex connector and in the air vent to the drain at the bottom of the chamber. Forty-nine machine cycles were tested with thermocouples in Group A positions, incorporating the following variables: (i) Tl temperatures between 70°C and 95°C in 5” steps; (ii) T2 temperatures between 70°C and 95°C in 5” steps; (iii) Tl holding times of either 3, 5, 7.5, 10, 12 or 15 min; (iv) T2 holding times of either 3 or 5 min with drying times of 5545 min. Ten machine cycles were tested with thermocouples in Groups B and C positions with TI set at 70°C for 5 min, T2 at 90°C for 3 min and with a drying time of 30 min.

Anaesthetic

Eficacy

equipment

washing

machine

403

of cleaning

Two standard soils were formulated to determine the cleaning ability of the machine. The Miles & Wolfe, Edinburgh, formula consisted of Egg yolk 100 ml, sheep blood 10% and hog mucin 2%. The Collins and Connelly, Birmingham, formula was made up of 5 g plain flour, 5 g hog mucin, 20 ml horse serum, 20 ml distilled water, 2% safranine solution (1 ml) and O-1 ml benzalkonium solution (used as a preservative but not included for tests where organisms were added to the soil). Soil was applied using an artists brush (a no. 7 pro-arte series B fine quality round) and allowed to dry at room temperature. Soil was applied to the following items: to the internal and external surfaces of the proximal and distal ends of the endotracheal tubes at positions L,, L, and R, and to the internal surface of the catheter mount at L,, on the upper manifold; to1 the proximal and distal ends of the respiratory hoses at B,, B,, B, and B,,, and to the Bain circuit at B, on the lower manifold. Items of equipment on thle tray that were test soiled included the black rubber bung, the Ambu face mask (internally and externally at the junction of the body and the pneumatic cuff), around the bulb area of the laryngoscope blade, the internal surface of the McGill suction union, the Heidbrink valve block, the internal surface of the two airways, the internal surfaces of a child’s face mask and the Leyland black rubber face mask and to the patient circuit connection area of the Mark 4a Absorber. The Birmingham soil is stickier than Edinburgh soil. Eleven cycles were run using Birmingham soil-for two of these, the soil was not allowed to dry onto items before washing. Twenty-three cycles were tested using Edinburgh soil-for one of these the soil was not allowed to dry. Internal soiling of two respiratory hoses at the centre of their length (B4 & BS) and of the centre of the length of one endotracheal tube (R2), followed by resealing of the tube using autoclave tape, was carried out during one cycle. In total, thirty-four cycles were tested with soil applied as detailed (but not at every site for all cycles). The cycles were tested over a range of temperatures and times, as detailed in the section on heat distribution. On the advice of the manufacturers, Extran M41 (British Drug Houses) was used as the detergent and M21 (BDH) as the rinse agent. A further fourteen cycles with soiled items were tested without detergent over a range of temperatures and times.

Heat disinfection using test organisms Streptococcus faecalis NCTC 10927 was cultured

overnight at 37°C in 20 ml Oxoid nutrient broth No 2. This culture was then pipetted into O-4 ml or 0.5 ml or 0.25 ml polypropylene microcentrifuge tubes with push fit caps (Alpha Laboratories). The test pieces contained about 10’ organisms/ml. The culture tubes were then attached to items in the washing machine using autoclave tape. After the machine cycles, Miles & Misra counts were

404

R. S. Miles

et al.

made on blood agar on the contents of the tubes. Direct culture from the tubes on to blood agar incubated at 37°C was also carried out. No growth of S. faecalis on the plates indicated that disinfection had been achieved. Control tubes of test organisms were taped to the wall of the room in which the washing machine was situated, and were similarly cultured. The test organisms were sited: F, and F,--inside the soda lime canisters; B,-at the distal end of the respiratory hose; Bs-at the proximal end of the respiratory hose; B,-at the distal end of the Bain circuit; L,, R, and R,-at the distal ends of the endotracheal tubes; R,-to the external surface of the airway and to the inside of the body of the Ambu mask and to the valve block on the tray. Thirty-six cycles were tested with culture tubes sited as detailed (but not at every site for all cycles). The cycles were tested over a range of temperatures and times as detailed in the section on heat distribution. Eight cycles were tested with S. fuecalis (approx. lo7 organisms/ml) incorporated in the Edinburgh soil. Areas of soiling as detailed above were sampled with a cotton swab moistened in nutrient broth (Oxoid) after washing cycles were completed. Swabs were cultured on blood agar and incubated at 37°C overnight. Control swabs were taken from items soiled but not washed and left at room temperature during the machine cycle. Drying of washed items A total of fifty-nine cycles

were

assessed.

Metering of water and energy consumption The services to the ANDA 9002 were metered using a kWh meter of the three electrical phases supplying the machine and individual on the hot- and cold-water supplies.

on each meters

Safety and design features An assessment was made. User satisfaction with machine performance Items of anaesthetic equipment, as shown in Tables I and II were repeatedly washed in the machine over a period of three months. Artificial soil was applied as detailed previously. New representative examples of equipment in current use in theatres in the UK were chosen for tests of the rate of deterioration. Some examples of new disposable equipment were included as it had been suggested that these might be used on more than one occasion following washing. These new items were located in manifold positions B,, B,, B,, B,, B,,; L,, L,, L,, L,, L,, L,; R,; F, and all items on the tray were included. Assessments were made of cleanliness and of the rate of deterioration of items. Particular attention was paid to the relationship between deterioration of items and washing times and temperatures.

Anaesthetic Table

equipment

1. Deterioration

washing

of equipment

Major *l *2. *3. *4. 5. 6.

machine following

405

washing

Minor Plastic airways Rubber airways Red rubber E/T tubes Latex E/T tubes Leyland face masks Disposable respiratory

* = no deterioration

1. Catheter mount and fitting 2. Sieman respiratory hose 3. Laryngoscope bulb

hoses

of replacement

test items

after

redesign

of upper

manifold.

12IlIO-

I

I7

9876-

/ i-5

I

54-

/

3-

\ qA4Ll

2-

I-

I

I2-

II-

IO-

0

IO 20

30

40

50

60

70 80

90

100

120

il0

Degrees

14c

130

centlgrode

Figure 3. Thermocouple readings with leads in Group B positions showing uniform temperature rise with negligible spread on reaching set Tl and T2 temperatures. l-5 thermocouples taped to load insert air and water inlets, to airway Rl, to reservoir bag at F8 and free in chamber. 6 thermocouple taped to outer surface of door, 7------thermocouple in hot water supply.

R. S. Miles

406

et al.

Results

Heat distribution Forty-nine machine cycles were tested with thermocouples in Group A positions and these cycles were used to establish guidelines to a satisfactory standard of machine performance. Ten cycles were tested with thermocouples in Group B and C positions. Group B positions provided close grouping of thermocouples (Figure 3) and the results were very similar to those obtained for Group A positions. Group C positions recorded temperatures at different sites on two load items during the drying stage (Figure 4). These latter ten cycles were run with set Tl (70°C for 5 min), and T2 (90°C for 3 min) temperatures and times (30 min drying time) close to those which would be used in a practical installation.

II I 8 7

6

: 5

4 !

0

Figure variation

IO

20

30

40 Degrees

50 60 centigrade

4. Thermocouple readings with leads in in the load during drying stage. 1 centre of hose at B8, 3 . . . . distal end reservoir bag at F7, 5 -----~ outside surface of in the air vent to the connector at LIO, 7 -

70

SO

90

Group C positions showing temperature proximal end of respiratory hose at B8, 2 of hose at B8, 4 -. - inside surface of reservoir bag at F7, 6 - ~ inside Portex chamber drain.

Anaesthetic

equipment

washing

407

machine

In all cycles it was evident that the temperature spread in the chamber was both even and well controlled. The set temperatures Tl and T2 were reached and held to within 1 or 2°C for the time determined by the programme card (Figure 3). Temperature rise was uniform, with negligible temperature spread on reaching set temperatures Tl and T2 for all The washing and rinsing locations measured in the evaluation. temperatures and times could be reliably achieved if the water temperature and pump-circulating pressure were maintained. There were considerable and non-repeatable variation s in temperature in the load throughout the drying stage (Figure 4). This was expected because air i.s used as the heattransfer medium and was not considered a defect, as long as the load could be shown to be consistently dry on completion of a standard operational cycle. The ambient room temperature stayed remarkably constant at between 28°C and 3O”C, indicating that the condenser system installed in the machine was effective. Cleaning eficiency Forty-eight machine cycles were tested over a range of Tl and T2 temperatures and times with soiled items in the load. For thirty-four cycles the recommended detergent was used and for fourteen cycles no detergent was used. Only three failures were noted-on a single occasion traces of soil were noticed in the interior of an airway placed in the tray for washing and on two occasions traces of soil were detected on an Ambu mask at the junction of the body and the detachable pneumatic cuff. (This mask was also set on the mesh tray for washing.) These failures occurred in cycles where Tl temperatures and times were 70°C for 5 min, 80°C for 7.5 min and 95°C for 15 min. No failures were recorded when cycles were run without detergent powder in the mac:hine and no failures were recorded in items washed on the manifolds of the machine. At no time during the evaluation were traces of detergent powdler detected on load items. Heat disinfection Thirty-six machine cycles were run with test pieces taped to items in the load. The cycles were tested over a wide range (70”-95°C) of temperatures and times (3-l 5 min). A further eight cycles were tested over a similar range of temperatures and times with S. faecalis incorporated into the Edinburgh soil. Disinfection was obtained in all cycles. Control test pieces and control swabs from soiled but unwashed items all yielded growths of S. faecalis. Drying of washed items A total of fifty-nine cycles were assessed. unsatisfactorily wet or damp after cycle occasions. T2 temperatures for these cycles drying times of 5-45 min. Thirty-five cycles yielded a dry load and in

The machine load remained completion on twenty-four ranged from 70”-90°C with these

cycles

the minimum

T2

408

R. S. Miles

et al.

temperature and drying times which provided a dry load were 80°C for 30min or 90°C for 20min. These machine settings were, however, unsatisfactory in other cycles. It was found that a T2 temperature of 90°C with a drying time of 30 min consistently produced a dry load. A washing, disinfecting and drying cycle using these settings, and with a Tl temperature of 7O”C, was consistently completed in 75 min. Water and energy consumption Five machine cycles were evaluated and the electrical consumption ranged from 4.6-5.3 kWh with an average of 5 kWh. Slightly less electricity was used when consumption was measured while the machine was still hot after a previous cycle. Hot-water consumption was consistently 54 litres per cycle and cold-water consumption ranged from 190-198 litres per cycle with an average of 194 litres. Safety and design features The general standard of construction of the machine was good with a stainless steel housing and a high standard of finish. The individual components of the machine appeared, in general, to be of a quality which should ensure a good service life while not requiring excessive maintenance. The machine does conform to current electrical standards and is safe in operation with adequate interlocks provided. The load insert is adequately located between the interlocking doors and misalignment was not practically possible. The maximum recorded temperature of the door surfaces during cycles was 41°C. User satisfaction Artificial soil was used to contaminate equipment in parts vulnerable to contamination during normal clinical usage. Residual soiling was detected on only three occasions, as detailed previously. Alteration in shape, consistency or function, to the extent that equipment became totally unserviceable, was classified as major deterioration. Visible changes in colour or consistency but where the equipment remained usable, were deemed minor deteriorations. The results are shown in Table I. All items held in clips (Ll-10 & Rl-10) were damaged after a single wash and were distorted by the combined effects of heat and the pressure of the holding clips. Only the catheter mount escaped serious damage as it was held by its firm junctional part. Disposable hoses lost their even consistency and the walls developed areas of weakness which could predispose to kinking. Non-disposable plastic hoses tended to darken and harden slightly but remained functional. After five machine cycles, Leyland face masks developed stickiness of the rubber of the pneumatic cuff, and the cuff itself became loosened from the body of the mask because of deterioration of the adhesive. The rubber insulating washer of the bulb in the laryngoscope blade showed deterioration after about

Anaesthetic

equipment

washing

machine

409

twenty machine cycles, although the bulb remained functional. It had, however, ceased to function by the end of the evaluation period. No differences in the pattern of deterioration could be observed in relation to different temperatures and times of the washing, rinsing and drying cycles. Other items were washed repeatedly for more than 70 cycles without deterioration. The infant size (Size 0) airway was washed off the open mesh tray on several occasions. This was prevented by providing a stainless steel cage on the tray. The machine could be loaded in 10-l 5 min by operating department attendants or other ancillary staff. Unloading took about 10 min, but the evaluation did not include estimation of time required for packaging. Discussion

No standard time/temperature relationship is agreed for washer/ disinfectors for anaesthetic equipment although Deverill and Dutt (1980) have made recommendations for the disinfection of anaesthetic equipment. Gurevich et al. (1983) considered that hot water machine-assisted cleaning of respirator tubing was less effective than chemical disinfection. Guidelines do exist for bedpan washers (Collins & Phelps, 1984), for hospital dishwashers [Department of Health and Social Security (DHSS), 19811 and for hospital laundry washers (DHSS, 1971). During this evaluation the attainment of similar standards to those suggested for bedpan washers were accepted as evidence of adequate heat disinfection. Biological tests of broth cultures of S. faecalis (Nilehn, 1972; Ayliffe, Collins & Deverill, 1974) provided further useful evidence of thermal disinfection. The results of the evaluation were most encouraging. Cleaning of items in the load was generally very satisfactory over a wide range of Tl (wash cycle) temperatures and times. The three failures that occurred were in single items from an entire load and the items were all placed on the open mesh tray for washing. It proved impossible to reproduce the failure to decontaminate an airway placed on the tray, and the failure to clean soil from an Ambu mask at the junction of body and cuff was considered insignificant by the users. It was concluded that the washer was extremely effective but if items with a lumen are washed on the mesh tray they should be examined carefully before clinical use. The temperature (Tl) of the wash cycle was not seen to be critical and an arbitrary temperature of 70°C was chosen and is suggested for a practical installation. The Tl time was also not critical and a time of 5 min was considered suitable. Thermal disinfection, as judlged by the results of the biological tests, was entirely satisfactory over a wide range (70-95”(Z) of temperatures and times (3-l 5 min). The temperature of the rinse or disinfecting cycle (T2) was not critical in

410

Et. S. Miles

et

al.

terms of disinfection but was seen to be important in obtaining a dry load. A minimum T2 temperature of 90°C was found to be essential for this and it was found that, in conjunction with a drying time of 30 min, a satisfactory total cycle time of 7.5 min could be achieved. The T2 time was not critical and a 3-min rinse cycle was considered adequate. Longer T2 times offered no reduction in the necessary drying time and simply prolonged the total cycle time. The design of the machine was satisfactory, although it was considered that the general layout of electrical components and the machine internal wiring could be more practical. The segregation between the electrical and water services could also be improved. The machine conforms to current electrical standards and any changes made would be only to ease maintenance and improve the overall visual impression given by the machine. A lockable cover over the adjustable Tl, T2 controls and the prepunched plastic control card slot would be advantageous in order to prevent unauthorised tampering with controls. One machine failure occurred during the early part of the evaluation when a hot-air hose to the base of the chamber became detached. This may have been loosened during transit or during installation. The cold water consumption of the machine (average per cycle 194 1) was much greater than that quoted by the manufacturers (15 1) for the basic machine. It appeared that this was due to water used by the built-in condenser. Serious distortion of items held in spring clips at positions Ll-10 and Rl-10 was noted after a single machine cycle. The problem was solved by redesigning the upper manifold to allow removal of the clips, trebling the length of the jets and angling the jet upwards at 45”. Black rubber face masks of Leyland type quickly became unserviceable when washed in this machine and we cannot recommend it for this purpose. Deterioration of Ambu type face masks was not detected. No attempt should be made to re-use disposable respiratory hose after washing in this machine. The claims made by the manufacturer with regard to the washing, disinfecting and drying of anaesthetic equipment, were, to a large extent, substantiated in this evaluation. It was concluded that a wash cycle of 5 min at 7O”C, with a rinse cycle of 3 min at 90°C followed by 30 min drying time, would consistently produce a clean, dry and disinfected load within 75 min. If this type of machine were to be installed in hospitals there would be no requirement for separate washing machines or low-temperature steam autoclaves and cabinet driers. Considerable capital and revenue saving would therefore accrue to the Health Service. We thank Ann Spencer the Common Services

for typing Agency.

the manuscript.

This

work

was supported

by a grant

from

Anaesthetic

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washing

machine

411

References Ayliffe,

G. A. J., Collins, B. J. and Deverill, C. E. A. (1974). Tests of disinfection by heat in a bedpan washing machine. Journal of Clinical Pathology 27, 76&763. Collins, B. J. and Phelps, M. (1984). The evaluation of bedpan washer/disinfectors. Journal of Sterile Services Management 2, 1 O-1 1. Collins, B. J., Phelps, M., Oates, K., Cripps, N., Viant, A. & Deverill, C. (Eds). (1986). Central Sterilising Club Report No. 1~ Washer/Disinfection Machines. Department of Health and Social Security. (1981). Health Service Catering Manual, “Hygiene” 2nd Edn., Catering and Dietetic Branch. London: HMSO. Department of Health and Social Security. (1971). Hospital laundry arrangements HM(71)49. London: HMSO. Deverill, C. E. A. & Dutt, K. K. (1980). Methods of decontamination of anaesthetic equipment: daily sessional exchange of circuits. Journal of Hospital Infection 1,165170. Feeley, T. W., Hamilton, W. K., Moyers, J., Xavier, B. & Eger, E. I. (1980). Sterile Breathing Circuits and post-operative infection. Anaesthesiology 53 (Suppl. 3), 392. Gurevich, I., Tafuro, P., Ristuccia, P., Hermann, J., Young, A. R. & Cunha, B. A. (1983). Disinfection of respirator tubing: a comparison of chemical versus hot water machineassisted processing. Journal of Hospital Infection 4, 199-208. Lumley, J. (1976). Decontamination of anaesthetic equipment and ventilators. British Journal of Anaesthesia 48, 3-8. Nilehn, B. (1972). A method for the quantitative microbiological check of heat decontaminators. Scandinavian Journal of Infectious Diseases 4, 245-253. Scottish Home and Health Department. (1985). Patient connected medical equipment service centre. Hospital Planning Note 7. London: HMSO.