An environmental survey of compliance with Occupational Exposure Standards (OES) for anaesthetic gases

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1 An environmental survey of compliance with Occupational Exposure Standards (OES) for anaesthetic gases K. A. Henderson 1 and I. P. Matthews 2 1 Environmental Adviser, Health and Safety Unit, and 2 Reader, Epidemiology and Public Health, University of Wales College of Medicine, Heath Park, Cardiff CF14 4XN, UK Summary Environmental monitoring of nitrous oxide and volatile agents was carried out between August 1996 and October 1997 within operating theatre areas in eight hospitals within the Bro Taf Health Authority. Static monitoring and personal sampling were undertaken to assess compliance with the Occupational Exposure Standards introduced in January 1996 by the Health and Safety Executive for anaesthetic agents. The monitoring concentrated on nitrous oxide with the results showing that compliance was being achieved. Limited monitoring was carried out of the volatile agents, which again were well below the Occupational Exposure Limits. Monitoring was also carried out in nontheatre areas in which anaesthetic agents were used. The results show that many of these locations, such as delivery suites and radiology units, have inadequate ventilation and no anaesthetic gas scavenging, both of which combined to produce levels that exceeded the standards. Keywords Anaesthetics, gases; trace concentrations. Anaesthetics, volatiles; trace concentrations. Operating rooms; exhaust systems.... Correspondence to: Dr I. P. Matthews Accepted: 16 April 1999 Occupational Exposure Standards (OES) were introduced for the four main anaesthetic gases in January 1996: nitrous oxide 100 ppm; halothane 10 ppm; iso urane 50 ppm and en urane 50 ppm [1]. These form part of the Control of Substances Hazardous to Health Regulations 1994 (COSHH) [2], with limits based on an 8 h time-weighted average (TWA). The limits were set as a consequence of alleged adverse effects associated with human exposures [3, 4]. The aim of the environmental survey was to establish whether there was compliance with the standards set for the anaesthetic agents. Methods The survey was carried out in all eight hospitals with operating theatres within the Bro Taf Health Authority in South Wales. Exposure to nitrous oxide was monitored in the anaesthetic room, operating theatre and the recovery room. A total of 81 static monitoring sessions and 97 personal samples were completed for nitrous oxide. A total of 374 anaesthetic inductions were monitored and each monitoring session was carried out for the duration of the operating theatre list. In addition to the main study, two subsidiary studies were undertaken. The rst measured volatile levels in two hospitals and the second investigated the use of anaesthetics outside the operating theatre within hospitals in Cardiff. Static monitoring was carried out using a Foxboro MIRAN 1B infrared spectrophotometer. Wherever possible the MIRAN was placed within 3 m of the anaesthetic machine. Gases are brought into the analyser by the ambient air pump at a rate of 30 l.min 1. A squirrel datalogger attached to the MIRAN was set to record at 10 s intervals in the anaesthetic room and operating theatre and at 1 min intervals in the recovery room. Nitrous oxide was sampled at a wavelength of 4.68 mm and iso urane was sampled at a wavelength of 8.84 mm. When possible, the static monitoring in the anaesthetic room and the operating theatre was carried out for the 941

2 K. A. Henderson and I. P. Matthews Compliance with OES for anaesthetic gases Anaesthesia, 1999, 54, pages 941±947 duration of an operating list. Static monitoring in the recovery room was for the duration of the working day. Personal sampling was carried out following the National Institute of Occupational Safety and Hygiene (NIOSH) sampling method 6600 [5]. This method was chosen because it was the most practical method of personal monitoring for this particular study and the results could be analysed immediately after the monitoring had been undertaken. A Negretti personal sampling pump connected to a 1 l reservoir bag was attached to the anaesthetist in order to obtain a sample of the working atmosphere within the breathing zone. The reservoir bags were left on for 20 min, either during the anaesthetic induction, or in theatre or the recovery room. The contents of the reservoir bags were then analysed using the MIRAN. In the operating theatre, samples were taken during the operation but did not include the transfer time into theatre or exit from the theatre, since this would not present a true picture of the working atmosphere. In the recovery room personal samples were taken from recovery room staff who were in the breathing zone of recovering patients. Results The results show that there is compliance with the standards set (Tables 1 and 2). High levels of nitrous oxide were observed during the monitoring although the TWA levels lay within the OES. Ambient and personal levels of nitrous oxide were lowest in the operating theatres where the most effective methods of control are in place. Personal sampling recorded higher levels in recovery rooms; this re ects the levels of waste anaesthetic gases being exhaled and the close proximity of the recovery staff to the patients. Provision of active gas scavenging in at least some recovery rooms may be desirable. A subsidiary study of the volatile agents in two hospitals, Table 1 Static monitoring of nitrous oxide Anaesthetic room Operating theatre Recovery room Peak Mean Time Peak Mean Time Peak Mean Time Hospital (ppm) (ppm) (min) (ppm) (ppm) (min) (ppm) (ppm) (min) Large teaching ± ± ± Day surgery ± ± ± ± ± ± Emergency and trauma ± ± ± ± ± ± ± ± ± Orthopaedic ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Large general ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Large general ± ± ± ± ± ± Small general ± ± ± General ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 942

3 K. A. Henderson and I. P. Matthews Compliance with OES for anaesthetic gases Table 2 Personal sampling of nitrous oxide and iso urane Iso urane Nitrous oxide Grand No. locations Mean level Range No. locations mean level Range Location monitored (ppm) (ppm) monitored (ppm) (ppm) Anaesthetic room (0±126) 12 1 (0±2) Operating theatre (0±97) 3 3 (2±3) Recovery room (4±114) 6 1 (0±2) Figure 1 Levels of nitrous oxide in the delivery suites of (a) hospital 1 and (b) hospital 2. (a) Average reading ˆ 480 ppm (35 min), occupational exposure limit ˆ 100 ppm (8 h time-weighted average). (b) Average reading ˆ 214 ppm (2 h), occupational exposure limit ˆ 100 ppm (8 h time-weighted average). 943

4 K. A. Henderson and I. P. Matthews Compliance with OES for anaesthetic gases Anaesthesia, 1999, 54, pages 941±947 Figure 2 Levels of (a) halothane and (b) nitrous oxide in the CT scanner room. (a) Average reading ˆ 21 ppm (30 min), occupational exposure limit ˆ 10 ppm (8 h time-weighted average). (b) Average reading ˆ 787 ppm, occupational exposure limit ˆ 100 ppm (8 h time-weighted average). measured by static monitoring gave grand mean levels of iso urane, in six anaesthetic rooms (0.5 ppm), ve operating theatres (0.5 ppm) and three recovery rooms (0.5 ppm). The personal samples obtained for iso urane were very low, with little difference between the anaesthetic room, operating theatre and the recovery room samples (Table 2). The second of the subsidiary studies looked at exposure in radiology and delivery suites. When nitrous oxide was the agent monitored, on a number of occasions the levels recorded over a relatively short period resulted in levels exceeding the 8 h TWA of 100 ppm. Figure 1(a,b) shows the levels achieved in delivery suites with no gas scavenging while entonox was being used. These gures re ect the high levels of waste anaesthetic gas that midwives are exposed to on a regular basis. Figure 2(a,b) shows the levels recorded in a CT scanner suite during a gaseous induction. This area did not have any gas scavenging so that very high levels of both nitrous oxide 944

5 K. A. Henderson and I. P. Matthews Compliance with OES for anaesthetic gases and halothane were recorded. Figure 3, from a radiotherapy unit, shows the levels of nitrous oxide in an unscavenged anaesthetic room and operating theatre. One personal sample from the anaesthetist in the CT scanner room showed the levels of exposure to nitrous oxide over a relatively short period would give almost the entire occupational exposure `dose' for the whole working day. During the survey it became apparent that anaesthetic practice in uenced the level of gases signi cantly. Figure 4 shows a monitoring session carried out in an anaesthetic room. On this occasion, two anaesthetists were alternating to induce anaesthesia. The graph highlights the different techniques employed, showing the difference between turning the gases off during intubation (the lower peaks) and leaving them on during this procedure (the higher Figure 3 Levels of nitrous oxide in the anaesthetic room and operating theatre (oncology hospital). Figure 4 Levels of nitrous oxide in the anaesthetic room (general hospital). Average reading ˆ 19 ppm (3.5 h), occupational exposure limit ˆ 100 ppm (8 h time-weighted average). 945

6 K. A. Henderson and I. P. Matthews Compliance with OES for anaesthetic gases Anaesthesia, 1999, 54, pages 941±947 Figure 5 Nitrous oxide levels before and after anaesthetic gas scavenging is switched on. peaks). Figure 5 shows the differences between anaesthetic inductions carried out with the anaesthetic gas scavenging switched on and switched off. On this occasion it was a complete oversight; however, it provided valuable information about the extent of the in uence of gas scavenging on the pollution generated during anaesthetic induction. With the scavenging switched on, it could be predicted that the pollution levels could be reduced by almost 50%. Discussion The research showed that compliance was being achieved for nitrous oxide in theatre areas and that it can be assumed that the levels generated from the volatile agents are usually well below the occupational exposure limits for each of the agents. It is accepted in the guidance document `Anaesthetic agents: controlling exposure under COSHH' that where nitrous oxide and volatile agents are being used together, if nitrous oxide is below the levels set, the levels of volatile agent are also being controlled. However, areas outside the operating theatre, such as delivery suites and radiology suites, were not complying. This was mainly as a result of lack of control measures and inadequate ventilation. Control measures are known to be effective [6, 7]. Clinical directors and consultants responsible for nontheatre locations should therefore assess exposures and methods for their control in order to comply with legislation. The survey aimed to investigate a cross-section of operating lists and therefore did not concentrate on any one type of surgery. However, it became apparent from the monitoring carried out that paediatric anaesthesia was one area in which improvements could be made. Currently there is no satisfactory form of anaesthetic gas scavenging for paediatric anaesthesia. A solution to this problem could reduce pollution levels in a high proportion of paediatric lists and this needs urgent attention. Anaesthetists who chose not to use nitrous oxide did so because they preferred to use oxygen and air. More anaesthetists would possibly choose to use oxygen and air during induction if air was available in the anaesthetic room. Of the hospitals monitored, 80% did not have the facility to use air on the anaesthetic machine. During the study, it was found that few anaesthetists were familiar with the occupational exposure standards, set in the UK, for the substances that they work with daily. It is recognised that each anaesthetist develops a personal technique when carrying out a procedure. However, some simple measures to reduce pollution were identi ed, such as turning off the gas ow during intubation, and ensuring that the gases are turned off before transferring the patient into the theatre. These simple procedures are not always being carried out at the moment. References 1 Health Services Advisory Committee. Anaesthetic Agents: Controlling exposure under COSHH. London: HMSO, Control of Substances Hazardous to Health (COSHH) Regulations. Approved Codes of Practice. London: HMSO, 1994, ISBN

7 K. A. Henderson and I. P. Matthews Compliance with OES for anaesthetic gases 3 Rodgers B. Exposure to waste anesthetic gases. American Association of Occupational Health Nurses Journal 1996; 34: 574±9. 4 Yagiela JA. Health hazards and nitrous oxide: a time for reappraisal. Anaesthetic Progress 1991; 38: 1±11. 5 National Institute of Occupational Safety and Health. Analytical Method 6600, Davernport HT, Halsey MJ, Wardley-Smith B, Bateman PE. Occupational exposure to anaesthetics in 20 hospitals. Anaesthesia 1980; 35: Ilsley AH, Crea J, Cousins MJ. Assessment of waste anaesthetic gas scavenging systems under simulated conditions of operation. Anaesthesia and Intensive Care 1980; 8: 52±