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Occupational exposure to inhaled anesthetic: Is it a concern for pregnant women?
Samar Shuhaiber; Gideon Koren, MD, FRCPC
Two of my pregnant patients are exposed to inhaled anesthetic on the job. One is an anesthetist, and the other is a veterinarian. They have both expressed concern about this exposure. How should I advise them?
Occupational exposure to waste anesthetic gas is not associated with increased risk of major malformations. Risk of spontaneous abortion might be slightly increased, however. This risk can be reduced, if not eliminated, by good gas scavenging systems.
Currently, 854 anesthetists practise in Ontario; 25% of them are women, and 46% of those are of childbearing age, according to the Ontario Physician Human Resources Data Centre at McMaster University in Hamilton, Ont. The College of Veterinarians of Ontario indicates there are 2745 practising veterinarians in the province; approximately 45% of them are women.1 Although there are numerous studies in the medical literature on the effects of occupational exposure to waste anesthetic gas (WAG) on the reproductive system, to date there have been no prospective controlled studies.
There are more data on the effects of exposure to WAG on pregnant women working in operating rooms than on those working in the veterinary field. Most existing evidence does not associate occupational exposure to WAG with increased risk of congenital malformations.2-11
Association with spontaneous abortion
A recent meta-analysis showed, however, that occupational exposure to WAG is associated with increased risk of spontaneous abortion (relative risk 1.48, 95% confidence interval 1.4 to 1.58).12 This meta-analysis included 19 studies of various designs with anesthetists, operating-room physicians and nurses, dental assistants, operating-room workers, hospital workers, health workers, and veterinarians and veterinary assistants as subjects. Most of the studies included in the meta-analysis were conducted before WAG scavenging had become a legal requirement, and none of the studies attempted to establish a relationship between amount of exposure and magnitude of risk of spontaneous abortion. The most important limitation is that all the studies were retrospective.
In the veterinary field, Johnson et al13 have shown that even though the odds ratio (OR) for spontaneous abortion after exposure to WAG among female veterinarians and female veterinary assistants was greater than 1.0 when adjusted for use of diagnostic x-ray machines, it did not reach statistical significance. Schenker et al14 demonstrated that rates of spontaneous abortion and low birth weight infants were statistically similar among female veterinarians and lawyers.
It is a misconception that concentrations of WAG are much greater in veterinary facilities than in human operating rooms. Ward and Byland15 measured WAG levels of 2 parts per million (ppm) in veterinary facilities and 10 ppm in human hospitals. Even though average room size in veterinary practice is smaller, operating times are short, and doors of veterinary surgery rooms are normally left open to allow technicians to work concurrently in other rooms.15 In addition, veterinary staff spend only a small portion of their working time performing surgeries.15 Despite all these factors, the level of WAG in veterinary facilities depends primarily on the presence of gas scavenging systems, good anesthetic practices, and periodic examination and maintenance of anesthetic machines.
Most of the studies did not differentiate between the various inhaled anesthetics because subjects were anesthetists, operating room staff, or hospital staff who were exposed to mixtures of gases. A few studies examined the association between occupational exposure to nitrous oxide and spontaneous abortion among dental assistants and midwives.
Studies on dental staff’s exposure to WAG had conflicting results. Cohen et al16 showed an increased risk of spontaneous abortion among dental assistants exposed to nitrous oxide (Pvalue not reported). Heidam,17 on the other hand, showed no increased risk for dental assistants either practising in private clinics or working in dental school services (OR 0.4). Last, Rowland et al18 demonstrated increased risk of spontaneous abortion among dental assistants exposed to nitrous oxide for 3 or more hours weekly in places without scavenging systems.
A study of Swedish midwives exposed to nitrous oxide in more than 50% of deliveries showed no increased risk of spontaneous abortion (OR 0.95). The effect of WAG scavenging was excluded because many midwives were unsure about whether such equipment had been present in the delivery rooms.19
These findings clearly indicate that the question of whether occupational exposure to nitrous oxide increases risk of spontaneous abortion is complicated. The answer depends on the field in which nitrous oxide is being used because this dictates duration of exposure and anesthetic techniques used.
Pregnant patients should aim to minimize their exposure to WAG by always using scavenging systems, by periodically testing anesthetic machines for gas leaks, and by not emptying or filling vaporizers. We also recommend good anesthetic techniques including use of cuffed endotracheal tubes whenever feasible, avoiding use of anesthetic chambers or masks (veterinary staff), and maintaining connections between animals and anesthetic machines such that animals breathe pure oxygen for a few minutes once vaporizers are switched off (veterinary staff). Monitoring WAG is possible through air sampling, dosimeter badges, and portable infrared analyzers, but monitoring is costly and, therefore, not routinely practised.
Currently, the Motherisk Program at The Hospital for Sick
Children, in collaboration with the Ontario Veterinary Medical
Association and the Ontario Association of Veterinary Technicians, is
conducting the first prospective study of occupational exposures of
veterinary staff during pregnancy; inhaled anesthetics are one of the
exposures. If you have patients who work in veterinarians’ offices and
would like to enrol them in our study, call or direct your patients to
call Samar Shuhaiber at (416) 813-6780.
- Osborne D. Changing gender demographics. J Ont Vet Med Assoc 1999;18(5):15.
- Lauwerys R, Siddons M, Misson CB, Borlee I, Bouckaert A, Lechat MF, et al. Anaesthetic health hazards among Belgian nurses and physicians. Int Arch Occup Environ Health 1981;48(2):195-203.
- Rosenberg PH, Vanttinen H. Occupational hazards to reproduction and health in anaesthetists and paediatricians. Acta Anaesthesiol Scand 1978;22:202-7.
- Ad Hoc Committee on the effect of trace anesthetics on health of operating room personnel, American Society of Anesthesiologists. Occupational disease among operating room personnel: national study. Anesthesiology 1974;41(4):321-40.
- Tomlin PJ. Health problems of anaesthetists and their families in the West Midlands. BMJ 1979;1:779-84.
- Spence AA, Cohen EN, Brown BW Jr, Knill-Jones RP, Himmelberger DU. Occupational hazards for operating room–based physicians. Analysis of data from the United States and the United Kingdom. JAMA 1977;238:955-9.
- Hemminki K, Kyyrönen P, Lindbohm ML. Spontaneous abortions and malformations in the offspring of nurses exposed to anaesthetic gases, cytostatic drugs, and other potential hazards in hospitals, based on registered information of outcome. J Epidemiol Community Health 1985;39(2):141-7.
- Sass-Kortsak AM, Purdham JT, Bozek PR, Murphy JH. Exposure of hospital operating room personnel to potentially harmful environmental agents. Am Ind Hyg Assoc J 1992;53(3):203-9.
- Axelsson G, Rylander R. Exposure to anaesthetic gases and spontaneous abortion: response bias in a postal questionnaire study. Int J Epidemiol 1982;11:250-6.
- Rosenberg P, Kirves A. Miscarriages among operating theatre staff. Acta Anaesthesiol Scand Suppl 1973;53:37-42.
- Cohen EN, Bellville JW, Brown BW Jr. Anesthesia, pregnancy, and miscarriage: a study of operating room nurses and anesthetists. Anesthesiology 1971;35(4):343-7.
- Boivin J. Risk of spontaneous abortion in women occupationally exposed to anaesthetic gases: a meta-analysis. Occup Environ Med 1997;54:541-8.
- Johnson JA, Buchan RM, Reif JS. Effect of waste gas and vapor exposure on reproductive outcome in veterinary personnel. Am Ind Hyg Assoc J 1987;48(1):62-6.
- Schenker MB, Samuels SJ, Green RS, Wiggins P. Adverse reproductive outcomes among female veterinarians. Am J Epidemiol 1990;132:96-106.
- Ward GS, Byland RR. Concentration of halothane in veterinary operating and treatment rooms. J Am Vet Med Assoc 1982;180:174-7.
- Cohen EN, Gift HC, Brown BW, Greenfield W, Wu ML, Jones TW, et al. Occupational disease in dentistry and chronic exposure to trace anesthetic gases. J Am Dent Assoc 1980;101(1):21-31.
- Heidam HZ. Spontaneous abortion among dental assistants, factory workers, painters and gardening workers: a follow-up study. J Epidemiol Community Health 1984;38:149-55.
- Rowland AS, Baird DD, Shore DL, Weinberg CR, Savitz DA, Wilcox AJ. Nitrous oxide and spontaneous abortion in female dental assistants. Am J Epidemiol 1995;141:531-8.
- Axelesson G, Ahlborg G Jr, Bodin L. Shift work, nitrous oxide exposure and spontaneous abortion among Swedish midwives. Occup Environ Med 1996;53:374-8.