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Anesthetic Gas And Pregnancy


Background: Studies of offspring of mothers exposed to anesthetic gases have shown associations with congenital anomalies reported by the mothers, but rarely in studies with objectively ascertained outcomes. We conducted a retrospective cohort study to examine associations between registry-ascertained congenital anomalies in offspring and anesthetic gas exposure of mothers employed as nurses.




anesthetic gas and pregnancy



Methods: A cohort of registered nurses in British Columbia, Canada, was linked to records of births and congenital anomalies from 1990 to 2000. Exposures were assessed via a survey of anesthetic gas use in all hospitals in the province and records of nurses' jobs, departments, and hospitals.


Results: Departments most frequently reporting anesthetic gas use were operating rooms, post-anesthetic recovery rooms, and maternity units. In the cohort of 15,317 live-borne children of 9,433 mothers, 1,079 had congenital anomalies. Anomalies were associated with ever and probable maternal exposure to halogenated gases (ORs: 1.49, 95% CI: 1.04-2.13; and 2.61, 95% CI: 1.31-5.18, respectively) and to nitrous oxide (ORs: 1.42, 95% CI: 1.05-1.94; and 1.82, 95% CI: 1.11-2.99). Anomalies most frequently associated with exposure were those of the heart (OR, halogenated gases: 2.31, 95% CI: 1.07-4.97) and integument (OR, halogenated gases: 3.56, 95% CI: 1.53-8.32; OR, nitrous oxide: 3.02, 95% CI: 1.37-6.64). Gases most frequently associated with anomalies were halothane (predominantly used early in the study period), isoflurane, and sevoflurane (predominantly used later in the period).


Work in operating theaters means exposure to high levels of stress and possible exposure to trace concentrations of waste anesthetic gases. Early in the 1970's concern arose about the possible effects of the risks of exposure to trace concentrations of waste anesthetic gases exerting effects upon nervous system and other body functions. Evidence for the reality of these concerns was seemingly confirmed by articles showing that:


All these general health and reproductive problems were attributed to trace concentrations of waste anesthetic gases in the operating theater air. Accordingly, an ad hoc committee of the American Society of Anesthesiologists (ASA) advised measures to reduce the trace concentrations of anesthetic gases in operating theaters (ASA advisory 1974). However, critical analyses of these studies during the later years of the 1980's revealed many of them to be seriously flawed. The main problem with all these earlier studies was that they were retrospective studies based upon voluntary responses to questionaires. Not everyone responds to such questionaires, and those most likely to respond are those who have had problems. This is why the results of these earlier studies were never confirmed by subsequent properly conducted prospective studies (Tannenbaum 1985, Mazze 1985, Buring 1985). So what is the truth regarding exposure to trace concentrations of waste anesthetic gases?


Pregnancy is an important life event, so it is only natural for everyone to be concerned. A pregnant woman has many questions, hopes, and fears. All hope for the delivery of a happy healthy baby. But not all pregnancies end this way. So what are the normal incidences, or percentage chances of events such as miscarriage, of ectopic pregnancy, of stillbirth, or of giving birth to a child with a birth defect?


The table below gives the percentage chances for miscarriage, ectopic pregnancy, and stillbirth for all births in Denmark from 1978 to 1992 (Nybo Andersen-2000). These statistics are comparable to those of other developed Western countries.


This table clearly shows that the most ideal age range for a woman to have children is in her 20's. Increasing maternal age is strongly associated with increased chance of miscarriage or ectopic pregnancy. Factors other than age predisposing to miscarriage are:


Most women working in the stressful environment of operating theaters are younger women in their reproductive years. The tables above clearly show there is about a 10% chance of miscarriage and a 3% chance of giving birth to a child with a birth deficit in the general populations of countries distributed across the world. These figures are significant. They mean that in any operating theater complex where many women work, one or more of these women will certainly experience a miscarriage or give birth to a child with a birth defect, even if there is no pollution of the air with trace concentrations of waste anesthetic gases.


So what is the current state of knowledge regarding the effects of trace concentrations of anesthetic gases? Careful analyses of all studies reveals there is no relationship between the presence of trace concentrations of waste anesthetic gases and abnormal health in people working in operating theaters. There is no increased chance of miscarriage, or of giving birth to babies with birth defects by women working in operating theaters, nor in the female partners of men working in operating theaters. In fact, careful review of studies performed during the 1970's reveal them to be flawed, and subsequent studies fail to show any relationship between cancer, liver and kidney disease, and disturbances of pregnancy related to trace concentrations of waste anesthetic gases (McGregor 2000).


Trace concentrations of anesthetic gases in the atmosphere of operating theaters have no known adverse effects on general health or pregnancy. Nonetheless, it is always better to limit exposure of trace concentrations of anesthetic gases to low concentrations you know are low, rather than take the chance of health problems due to unknown concentrations of these same anesthetic gases. For this reason, many countries have instituted, and enforce, strict regulations for acceptable levels of trace concentrations of waste anesthetic gases in operating theaters (McGregor 2000a, Mazze 1985). This is simply good workplace practice to ensure the health and wellbeing of all working there.


Our findings indicated that the cell cycle disturbance of the neural progenitors in the fetal PFC contributed to aberrant proliferation and differentiation after maternal sevoflurane exposure, which may finally lead to the functional neurological impairments in adult offspring. Our study helped to understand the mechanism of postoperative neurological impairments after prenatal sevoflurane exposure and appealed people to consider the neurotoxicity of anesthetics when considering the benefits and risks of nonobstetric surgical procedures.


While some small degree of waste anesthetic gas exposure is almost inevitable in veterinary medicine, the National Institute for Occupational Health & Safety (NIOSH) recommends that concentrations of 2 ppm (parts per million) should not be exceeded in the workplace. In reality, however, there is no known safe exposure level.


If an anesthesia circuit is leaking waste anesthetic gases during surgery, for example, the surgeon and anesthetist may start to experience headaches, fatigue, or nausea early during the course of surgery. Long-term effects of waste anesthetic gas exposure, however, are more variable and difficult to quantify.


These can include liver damage, kidney damage, reproductive disorders, neurologic disorders, hematopoietic changes, and neoplasia. Although a number of studies have been performed regarding the effects of long-term waste anesthetic gas exposure, direct cause-effect relationships still have not been fully established. Therefore, it is ideal to minimize long-term waste anesthetic gas exposure as much as possible.


Effective scavenging is a crucial method of decreasing waste anesthetic gas exposure in the workplace. Scavenging systems remove waste anesthetic gases from the anesthesia breathing circuit and vent these gases to the outdoors.


A passive scavenging system operates without the use of suction, since the positive pressure of gas in the breathing circuit pushes waste anesthetic gases into the scavenging system. One-way valves in the interface help move waste anesthetic gases outdoors or into a non-recirculating air ventilation system. A passive scavenging system does not involve the use of a vacuum pump or suction.


While scavenging systems play a valuable role, veterinary team members must follow a number of additional guidelines to further decrease waste anesthetic gas exposure to themselves and their colleagues.


Close the breathing circuit (connect circuit and rebreathing bag, close pop-off valve, occlude y-piece) and pressurize the circuit (to approximately 30 cmH2O2). Observe to determine whether the pressure within the circuit holds or whether it falls quickly. A rapid decrease in pressure indicates a leak within the anesthetic circuit, which could lead to waste anesthetic gas exposure.


Box and mask inductions can allow large quantities of waste anesthetic gases to enter the veterinary treatment area. These inductions should be avoided unless absolutely necessary (for example, with exotic patients that cannot be intubated).


Even after five minutes on the anesthesia circuit, patients still exhale waste anesthetic gas in recovery. Recovery rooms can easily reach high waste anesthetic level gas levels when multiple pets are recovering from anesthesia simultaneously, especially if the room is small or lacks adequate circulation. Take this into account when determining where anesthetized pets will be recovered or designing a new practice.


It is impossible to avoid some waste anesthetic gas escape when refilling vaporizers. Vaporizers should be refilled in an empty, well-ventilated room at the end of the day, instead of in a busy treatment area at the start of the work day.


Employees should be regularly reminded of the risks of waste anesthetic gas exposure and how to minimize these risks. Management should ensure that recommendations are being followed on every anesthetic case performed in the practice.


While it is nearly impossible to avoid all waste anesthetic gas exposure, proper equipment and anesthesia monitoring techniques can significantly reduce this exposure and minimize risks to the veterinary team.


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