Occupational Exposure of Veterinarians to Waste Anesthetic Gases

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Abstract
An evaluation of anesthetic waste gas exposures was conducted in small private practice animal clinics throughout the Salt Lake Valley. The two most frequently used anesthetic gases, methoxyflurane and halothane, were chosen to be studied. Exposures during 38 surgeries were studied in a total of 10 facilities involving 13 veterinarians. Veterinarian breathing zones were sampled on a real-time basis with a Wilks Miran infrared analyzer. Several back-to-back surgeries were also monitored to determine the potential for gas build-up in the operating rooms. The monitoring results indicated that veterinarians have a significant exposure to anesthetic gases. Time-weighted averages over the anesthetic administration period ranged from 0.07 to 2.99 ppm for methoxyflurane and from 0.08 to 9.19 ppm for halothane. A low pressure leak test was performed on each piece of anesthesia equipment. Of the 20 machines checked, 55 percent did not meet the NIOSH recommendations concerning maximum leakage of 100 ml/min under 30 cm of water pressure. NIOSH further recommends that if leakage is greater than 1.0 1pm, the machines should not be used until repaired. Thirty percent of the units inspected exceeded this value. The oxygen flowrate, which determines the amount of anesthetic agent used, was not a function of animal size. This practice resulted in an excessive use of anesthetic agent for small animals. The halothane concentrations were higher than the methoxyflurane concentrations because of the out-of-circuit vaporizer design which requires higher oxygen flowrates. Overall, scavenging was found to be effective in reducing anesthetic gas exposures by 2.7-fold for methoxyflurane and 43-fold for halothane. However, during back-to-back surgeries a gradual build-up of anesthetic gas was found in the surgical rooms even with the use of scavenging equipment. This indicates a need for additional engineering controls. The use of a ceiling exhaust fan resulted in a 38-fold reduction in the exposure concentration. It appears that dilution air can provide effective control even for nonscavenged and poorly maintained anesthesia machines. It is recommended that a scavenging system along with good work practices and dilution ventilation be utilized to control anesthetic waste gas exposures in veterinary clinics.