Journal of Preventive Medicine

Introduction
Waste anesthetic gases (WAGs), despite their importance in medicine, are the most important source of air pollution in operating and recovery rooms [1, 2, 3]. A suitable approach to optimize the determination of occupational exposure to toxic substances and in accordance with the recommendations of the occupational safety and health administration is biological monitoring, which is far more important than determining the concentration of air pollutants, because, unlike environmental monitoring which only allows the measurement of the external dose by determining the average concentration of pollutants in the open air and cannot indicate the actual exposure [13], biological monitoring provides the possibility of evaluating the exposure to toxic chemicals in the work environment at certain times, through the measurement of appropriate indicators in biological samples [14]. Among the biological samples, to evaluate individual exposure to toxic pollutants, especially WAGs, measuring the concentration of compounds in the urine sample are more acceptable, due to simple and non-invasive sample collection and the fact that almost all toxic substances and their metabolites are excreted through urine [2]. The present study aims to determine the urinary concentration of WAGs (nitrous oxide, isoflurane, sevoflurane) and evaluate the toxic effects of long-term occupational exposure them in the operating room of a hospital in Shiraz, Iran.

Methods
This is a descriptive-analytical study with a cross-sectional design that was conducted in a large hospital located in Shiraz, Iran. A total of 60 people participated and divided into two groups of 30 including exposed and control groups. The exposed group included employees working in the operating and recovery rooms who had at least 3 years of exposure to anesthetic gases and were present in the operating room continuously in the past 3 months without leave. The people of the control group were selected from among the nurses of the inpatient departments and administrative staff who had no history of occupational or non-occupational exposure to any chemical compound. Demographic information was collected using a questionnaire. To measure the level of occupational exposure to WAGs, we used the method proposed by Accorsi et al. [2].

Results
In the exposed group, urinary concentration of nitrous oxide, isoflurane, and sevoflurane were 175.8±77.52, 4.95±3.43, and 15.03±16.06 μg/L of urine, respectively. However, none of the above WAGs were found in the urine samples taken from the control group. The mean concentration of all three WAGs was higher in the operating room staff than in the recovery room staff, and this difference was statistically significant only for nitrous oxide (P<0.05).

Conclusion
The mean urinary concentration of sevoflurane and especially nitrous oxide in the urine samples of operating and recovery room staff in the selected hospital is higher than their limit of detection, indicating that they are exposed to high concentrations of these WAGs during anesthesia and after surgery (exhalation of patients). The lack of proper and modern ventilation systems in the operating rooms and some unsafe actions by the staff, such as opening the gas flow before putting the anesthesia mask on the patient’s face, has caused the concentration of these pollutants, especially nitrous oxide, to be very high in the operating rooms. Therefore, to reduce the concentration of WAGs and the exposure of employees to them and the consequences of inhaling these gases, operating rooms should be equipped with a proper ventilation system (e.g. installing a local ventilation system above the anesthesia machine). Anesthesia machines and ventilators are among the most important sources of anesthetic gas leakage into the air of the operating room. Therefore, it is recommended to check them periodically (daily, weekly, monthly) and compile instructions for their maintenance and timely repair. Holding training classes on the limits of detection, ways of exposure, the role of ventilation system in reducing operating room air pollution, maintenance of equipment and devices in reducing operating, proper dispose of containers containing isoflurane and sevoflurane drugs, as well as the periodic examinations of operating room staff exposed to these pollutants should also be considered. Encouraging staff and implementing motivational programs to properly perform tasks and have appropriate behaviors such as cutting off the gas flow before removing the anesthesia mask from the patient’s face, closing the anesthesia machine when it is not in use, preventing the spilling of drugs in the work environment and quick cleaning, turning off the anesthesia machine when it is not in use, preventing the spilling of drugs in the work environment and quickly cleaning in case of spilling, and using anesthesia masks that fit the size of the patient’s face can also help reduce the amount of exposure to WAGs in operating rooms.

Ethical Considerations
Compliance with ethical guidelines
The protocol of the study was approved by the Ethics Committee of  Shiraz University of Medical Sciences, Shiraz, Iran (Code: IR.SUMS.RE C.1396.S388).

Funding
This study was financially supported by Shiraz University of Medical Sciences, Vice-Chancellor for Research and Technology (Grant No.: 96-01-04-14653) and also Iran National Science Foundation (Grant  No.: 96005391).

Authors' contributions
Methodology: Masoud Neghab; Investigation: Fatemeh Amiri, Alemeh Ebrahimi, Fariba Asadi Noghbi, and Fayegheh Zareei; Writing and final approval: Fatemeh Amiri.

Conflicts of interest
The authors declared no conflict of interest.

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