Anesthetic Waste Gas

Adopted: February 9, 2010

Last Review Date: October 10, 2017

I.  Purpose

The purpose of this policy is to protect the health of persons working with or near anesthetic gases used to sedate or euthanize animals at the University of Montana. Volatile anesthetic waste gases should be minimized through training in anesthetic administration, using the smallest amount of anesthesia necessary, maintaining anesthetic equipment in proper working order, scavenging anesthetic waste gases, and monitoring worker exposure.

II. Procedure

    A.  Approved Inhalant Anesthetic Agents

1.  Isoflurane is the only approved volatile halogenated anesthetic agents at the
     University of Montana.  Isoflurane may be used for both anesthesia and
     euthanasia with proper approval from the Institutional Animal Care and Use
2.  Nitrous oxide is not approved for use in any facilities at the University of Montana. 
     Its primary indication in veterinary medicine is as an adjunct to inhalant
     anesthesia for added relaxation and analgesia.  However, there are a variety of
     alternative injectable sedatives and analgesics that are efficacious and do not
     present health risks to personnel.

    B.  Anesthetic Training

1.  Training to ensure the safety of animals being anesthetized and of the persons in
     the area must be provided by the principal investigator (PI), Attending
     Veterinarian, Laboratory Animal Resources (LAR) staff, or a trained and
     experienced scientific laboratory member approved under the animal use
     protocol (AUP). 
2.  Training should include checking the anesthetic circuit for leaks, operating
     vaporizers at their lowest settings necessary for maintaining adequate anesthesia,
     use of scavenging equipment, and animal monitoring. 

   C.  Equipment Maintenance

1.  Vaporizers are fully cleaned and calibrated by an authorized exchange service
     center every other year.  In the years between the exchange, vaporizers are
     examined by a certified technician using leak and delivery accuracy testing on
2.  In both cases, vaporizers are marked with a sticker indicating the date of testing
     or the date of next needed maintenance. 
3.  Maintenance is scheduled through LAR or verification provided in writing to the
     Facility Manager.

   D.  Waste Gas Scavenging

1.  When using an anesthetic vaporizer, waste gas should be scavenged actively
     through a house vacuum, passively using a charcoal canister, or actively and
     passively [e.g., active anesthetic evacuation system (A.E.S., Surgivet) feeding a
     charcoal canister]. 
2.  Endotracheal tubes should have cuffs to prevent leakage, and animal face
     masks should fit snugly.
3.  When using the open-drop method in the laboratory (e.g., a closed jar containing
     gauze with anesthetic dripped on the gauze), it must be performed in a fume
     hood. Care should be taken to ensure that the liquid anesthetic does not come
     into direct contact with the animal.
4.  In the field, use of the open-drop method requires adequate ventilation, holding
     the jar at arm’s length when opening, and using a jar/container with a volume of
     500-1000 ml. Care should be taken to ensure that the liquid anesthetic does not
     directly contact the animal.

   E.  Worker Exposure Monitoring

1.  In the absence of established national guidelines for isoflurane, it is our practice to
     use 2 ppm as an institutional recommended exposure limit (REL).  Monitoring of
     personnel using badges clipped to clothing in the breathing zone will be done for
     all new anesthetic equipment and each new area of anesthetic use to verify that
     typical exposures are below the REL.  Changes in equipment or experimental
     conditions warrant additional monitoring.  It is the responsibility of the PI to inform
     the IACUC of such changes.
2.  The United States Department of Labor, Occupational Safety and Health
     Administration has published a document entitled "Anesthetic Gases: Guidelines
     for Workplace Exposures" at
    According to this document,

"In 1997, the National Institute for Occupational Safety and Health (NIOSH) … recommended that no worker should be exposed at ceiling concentrations greater than 2 ppm of any halogenated anesthetic agent over a sampling period not to exceed one hour (NIOSH 1977).  In 1989, the American Conference of Governmental Industrial Hygienists (ACGIH) assigned a threshold limit value-time-weighted average (TLV-TWA) for . . . halothane and enflurane, and are 50 ppm and 75 ppm, respectively. No NIOSH recommended exposure limits (REL) exist for the three most currently used anesthetics (isoflurane, desflurane, and sevoflurane). The levels of risk for isoflurane, desflurane, and sevoflurane have not been established. Since there are limited data, occupational exposure limits for these agents have not been determined. Therefore, until more information is available, it is prudent to attempt to minimize occupational exposure to these as with all anesthetic agents."