Waste Anesthetic Gases as a Veterinary Workplace Hazard

Waste anesthetic gases (WAGs) are inhalant anesthetics that escape into the veterinary clinic environment instead of being properly captured by scavenging systems. Common WAGs include halogenated agents such as isoflurane, sevoflurane, desflurane, and halothane, as well as nitrous oxide.

WAGs can leak from anesthesia machines, vaporizers, breathing circuits, uncuffed endotracheal tubes, and malfunctioning scavenging systems. WAGs can also be exhaled by patients during recovery. In addition, spills during vaporizer filling can contribute to environmental contamination. Poorly fitted masks and inadequate ventilation in surgical areas lead to greater inhalation of WAGs.

Occupational exposure of veterinarians and their staff to WAGs can result in adverse health effects (1). The impact can be classified into two categories: short-term exposure (fatigue, headache, dizziness, irritability) and long-term exposure (eg, potential reproductive, neurological, and hematologic toxicoses).

Hematologic effects associated with chronic WAG exposure include decreased RBC counts, with conflicting results reported for WBCs. Liver and kidney effects have also been reported, including increased levels of liver enzymes (AST, ALT, GGT, ALP) in exposed people (2).

Reproductive effects of WAGs have been widely studied (3, 4, 5). Some reports suggest increased risks of miscarriage or preterm delivery in personnel who work long hours in inadequately ventilated operating rooms without scavenging systems. However, current evidence suggests that when proper scavenging systems and ventilation are in place, female veterinarians exposed to anesthetic gases do not have a higher risk of reproductive issues compared with females who are not exposed (6).

There is limited and inconsistent evidence regarding congenital abnormalities and other long-term effects of exposure to WAGs. Some studies have identified potential DNA (genotoxic) effects associated with prolonged exposure (7).

The US National Institute for Occupational Safety and Health (NIOSH) recommends exposure limits of 2 ppm of halogenated anesthetics used alone (not exceeding 1 hour) and 0.5 ppm if used in combination with nitrous oxide for 1 hour of exposure. For nitrous oxide alone, this value is 25 ppm, accounting for the time-weighted average concentration during the use of this anesthetic agent (8). Exposure limits in other countries vary.

Control of WAGs in veterinary clinics is crucial. The primary control methods to decrease exposure to these hazardous gases is substitution and prevention:

• Substitution of inhaled agents with total IV anesthesia (eg, using drugs like propofol) or use of regional/local anesthetic techniques should be considered. Replacing desflurane or nitrous oxide with sevoflurane and utilizing low-flow techniques can decrease environmental and occupational exposure to WAGs.

• Preventive steps include improving ventilation (local exhaust and general dilution) and maintaining anesthetic equipment to prevent leaks. A minimum of 15 air changes per hour in operating rooms and 6 air changes per hour in recovery rooms has been recommended (7).

Guidelines for the control of WAGs in the veterinary workplace focus on equipment maintenance (including leak tests and routine vaporizer servicing), scavenging systems, and proper workplace practices.

Safer handling practices include filling vaporizers in a well-ventilated area or hood, filling vaporizers at night, and delaying turning on a vaporizer until the circuit is fully connected to the patient. Minimizing exposure time, using face masks, and using closed induction chambers can also decrease WAG concentrations.

Staff training and adherence to safety protocols also play an important role in decreasing WAGs in the environment.