A longitudinal study for investigating the exposure level of anesthetics that impairs neurobehavioral performance

There is conflicting evidence on the level of anesthetics that impairs neurobehavioral performance, leading to differences in exposure standards (25 or 50 ppm for N2O). Thirty-eight operating room nurses and 23 unexposed nurses were asked to provide information on confounding variables: age, gender, years of schooling, alcohol and coffee consumption, smoking, length of work, symptoms (Euroquest) and results of Block Design test. Afterward, all workers were repeatedly examined (on Monday and Friday of a working week, before and after workshift) for stress and arousal (Mood Scale) and complex reaction times (Color Word Vigilance, CWV), the latter being the outcome. Individual exposure was assessed through urinary end-shift concentrations of nitrous oxide (N2O) and isoflurane. According to the highest value of urinary excretion of N2O in the week, exposed workers were subdivided in three groups (<13; ≥13 and <27; and ≥27 μg/l). The values of 13 and 27 μg/l correspond to environmental concentrations of 25 and 50 ppm, respectively. In order to take into account the pre-existing abilities of exposed and reference workers, and investigate the neurobehavioral changes over time, longitudinal data were analyzed by a two-stage regression model and analysis of variance for repeated measures (MANOVA). The former method, controlling for confounding factors and Monday morning CWV (which conveyed the pre-existing ability of the subjects), showed that, with respect to unexposed nurses, reaction times were significantly (p < 0.020) higher only in workers with urinary N2O ≥ 27 μg/l. Therefore, at MANOVA, all subjects were categorized in two classes (N2O urinary concentrations < or ≥27 μg/l), and CWV results were adjusted for the confounding variables and effects of stress and arousal, taken concurrently with CWV. CWV significantly (p < 0.039) decreased over a working week (indicating a learning effect) in workers with urinary N2O < 27 μg/l, while remained steady (indicating impairment of neurobehavioral performance) in those with urinary N2O > 27 μg/l.