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Abstract

Occupational exposure to high concentrations of anesthetic gases (more than 500 ppm of nitrous oxide and more than 15 ppm of halothane and enflurane) can cause neurobehavioral effects in operating room personnel. Factors such as stress and work organization play an additional role in reducing performance capacities. It is still unclear whether these conditions may become the predominant factor in behavioral impairment when exposure to anesthetic gases is reduced; in addition, we wished to ascertain the extent of neurobehavioral and neuroendocrine effects at relatively low levels of exposure to such gases. Therefore the same group of 30 operating room personnel was examined with neurobehavioral tests during gaseous and nongaseous anesthesia. In this way, the neuropsychological performance was examined under the same stress conditions, but with different exposure levels to anesthetic gases. Serum cortisol was measured as an additional “biological stress indicator.” Prolactin secretion was examined to study possible interference of anesthetic gases with the dopaminergic system. The results were compared with those in a control group of 20 hospital workers from other departments, with similar characteristics in respect of age, sex, and education. During work with gaseous anesthesia, average airborne concentrations (geometric mean) of nitrous oxide were 50.9 ppm (SD 20.8) on the first day of the working week, and 54.2 ppm (SD 22.1) on the last day of the working week, whereas average urinary nitrous oxide (geometric mean) were 21.54 micrograms/l on the first day of the working week and 25.67 micrograms/l on the last day of the working week. The operating room workers showed slower reaction times at the end of the week with gaseous anesthesia, compared with workers using nongaseous anesthesia and the control group. At the same time they also showed increased secretion of prolactin, whereas cortisol remained unchanged. Therefore, it can be concluded that lower levels of exposure to anesthetic gases (and not only high exposure levels) cause an impairment of neurobehavioral performance, with the action of stress being less relevant. The mechanism of anesthetics’ neurotoxic action seems to be related to interference with the dopaminergic system.

*Original abstract online at https://link.springer.com/article/10.1007%2FBF00381630

 

Excerpt

Introduction

According to experimental and field studies, exposure to more than 500 ppm of nitrous oxide(N 2O) and more than 15 ppm of haJothane and enflurane can cause performance impairment in neurobehavioral exammations (Bruce and Bach 1975, 1976; Smith and Shirley 1978; Allison et al. 1979; Edling 1980; Mahoney et al. 1988. Control of exposure to anesthetic gases has received increased attention since the mid-1970s, when scavenging devices were fitted on anesthesia machines to vent the gases from the operating room. In the U.S. the National Institute for Occupational Safety andn Health (NIOSH) recommended in 1977 that exposure to N2O be limited to a time-weighted average (TWA) air concentration of 25 ppm, whereas the American Conference of Governmental Industrial Hygienists proposed a threshold limit value (TLV) of 50 ppm (ACGIH 1976). In 1989, the Italian Ministry of Health recommended a TLV-TWA of 100 and 50ppm, for already existing and for newly constructed operating rooms respectively (Ministero Sanita). The subsequent improvement of ventilation systems in workplaces led to a general decrease in exposure levels in most hospitals. Further neurobehav1oral field studies were subsequently conducted at concentration levels generally lower than 100 ppm of N 20, These studies showed that factors other than anesthetic gases, such as stress and work organization, may play an important role in determining performance impairment under these exposure conditions (Stollery 1988; Gilioii et al. 1992, Lucchini et al. 1995). Stress conditions activate the hypothalamic-adrenal system and cause hypersecretion of corticosteroids and catecholamines. When. in their daily activities, humans are subjected to mental, physical, or diverse environmental stresses, cortisol levels increase. These external stimuli provoke secretory peaks that interact with the physiological fluctuations due to circadian rhythm (Branderberger 1992; Tarui and Nakamura 1991; Lundberg et al. 1990). Therefore, serum cortisol can be used as a biological indicator or stress.

Recently, it was hypothesized that anesthetic gases have a similar mechanism of neurotoxic action to organic solvents. In fact. both substances might interfere with the dopaminergic system, which is very important in arousal and mood modulation. The tuberoinfundibular
system may be a specific target for these substances and/or their metabolites dissolved into the bloodstream, since it is not protected by the bloodbrain barrier. Moreover, the pituitary function can be selectively vulnerable and this effect is specifically shown by changes in prolactin (PRL) secretion, which is tonically modulated by the dopaminergic system (Mutti et at 1993).

Based on these observations, neurobehavioral functions, PRL secretion and serum cortisol were studied in operating room workers exposed to anesthetic gases at different times of the working week.

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