Anesthetic Gases

Anesthetic gases have been associated with toxic and chromosomal effects on the users. Investigations have shown that many of the anesthesia machines used in veterinary medicine have leaks that contribute to operating room contamination. Many others do not have appropriate scavenging attachments to remove escaping gases. Personnel have been frequently observed carelessly using equipment or handling anesthetic agents in a manner contributing to excessive exposure. Proper maintenance of equipment and careful use of gaseous anesthetic agents can significantly reduce waste gas levels and exposure of personnel (18).

In Austria, operating room personnel exposed to an 8-hour time-weighted average of 12.8 ppm nitrous oxide and 5.3 ppm isoflurane had a mean frequency of sister chromatid exchanges significantly higher than controls (19).

In Colorado, a survey of veterinarians in an 11-county region indicated that inhalation anesthetics were used in 80.8% of the 210 practices. Exposures to waste anesthetics in veterinary practices were far less than reported in human hospitals. Waste anesthetic concentrations were affected by size of the patient, type of breathing system, and use of scavenging systems. Dilution ventilation had no effect on breathing zone concentrations. The endo-tracheal tube and occasionally the anesthetic machine were the major sources of leakage of anesthetic gases (20).

In Canada, concerns were raised by several workers from veterinary clinics in Manitoba regarding potential exposure to isoflurane and halothane during anesthetic administration. No guideline have been established for isoflurane by the American Conference of Governmental Industrial Hygienist (ACGIH) or a permissible exposure limit by the Occupational Safety and Health Administration (OSHA) or a recommended exposure limit (REL) by the National Institute for Occupational Safety and Health (NIOSH). The ACGIH threshold limit value (TLV) time-weighted average (TWA) for halothane is 50 ppm and NIOSH has established 2 ppm as a recommended level based on a 1-hour sampling; OSHA has established no guideline for halothane. All veterinary clinics inspected had installed the passive waste gas scavenging system. Veterinarians' personal exposures for isoflurane ranged from 1.3 to 13 ppm, and for their assistants, personal exposures ranged from 1.2 to 9 ppm. Veterinarians' personal exposures for halothane ranged from 0.7 to 12 ppm; for their assistants, personal exposures ranged from 0.4 to 3.2 ppm. One clinic had significant leaks in the anesthetic gas delivery lines. Personal halothane exposure for the veterinarian at this clinic was 7.2 to 65 ppm. Peak exposures were recorded when the cuffed endotracheal tube was removed from the animal. Equipment leaks were minimal when the system was maintained at its optimum operating condition (21).

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