Anesthetic Gas Use

Halogenated anesthetics, such as isoflurane, are used as an animal anesthetic. These anesthetics are effected for the most part free of adverse effects on the animals to which they are administered. 

Hazards of Isoflurane

Health effects from short-term exposure include:  irritation to the eyes, skin, respiratory tract; cough, sore throat; headach, drowsiness, dizziness, asphyxia, and unconsciousness.  The health effectes from long-term exposure are largely unknown.  Halogenated anesthetics, in general, have been associated with reproductive problems in women and developmental defects in their offspring.

In 1977, the National Institute of Occupational Safety and Health (NIOSH) established an exposure limit of 2 parts per million (ppm), for no greater than one hour, on the halogenated anesthetics.  At that time, isoflurane use was not widespread.  According to the Occupational Safety and Health Administration (OSHA), "the weight of the evidence regarding potential health risks from exposure to anesthetic agents in unscavenged environments suggests that clinicians need to be concerned... a responsible approach to worker health and safety dictates that any exposure to waste and trace gases should be kept to the lowest practical level."

Risk Assessments and Exposure Monitoring

Risk Management and Safety staff are available to assess your surgery suite or work space to determine any risks of over exposure to anesthetic gases.  Safety staff can also provide exposure monitoring, using sampling badges, to determine whether a worker may be over exposed to anesthetic gases.  If results show an over-exposure Safety staff will work with the lab on solutions to reduce worker's exposure.  If you would like to talk to someone regarding the possible epxosure to anesthetic gas in your lab or to have exposure monitoring completed, please contact

Pregnant Workers

If you are pregnant or become pregnant while working in a lab at UVM, you should consult with your physician for their recommendations.  A SDS for the anesthetic gases utilitized as well as any other hazardous materials (chemicals, infectious materials, radioactive materials, physical hazards) you use in the lab should be shared with your physician.  Based on recommendations of your physician, alternative accommodations may be arranged. Arrangements may include performing surgery in an alternate work space, wearing respiratory protection while working with anesthetic gases, or limiting your exposure during the pregnancy. For more information, please see the safety guidelines for pregnant women in UVM's laboratories.

Steps to Minimize Exposures During Isoflurane Use:

General Room Ventilation

Animal surgeries, euthanasia, and perfusions must be performed in labs with general room ventilation that includes supply and exhaust.  Labs should have 10-12 fresh air changes per hour and be negative in air pressure with respect to adjacent areas.  It is recommended that animal surgery suites have higher air changes than a typical lab.

Local Ventilation

Whenever possible, anesthetic gas use should be conducted in a laboratory area with local ventilation.  Most labs have a fume hood accessible that could be used to reduce the risk of exposure to anesthetic gas during induction, surgery, and animal recovery.

Fume Hoods

Whenever possible, fume hoods should be used when opening bottles of anesthetics, when attaching fill keys to bottles, and when filling the vaporizer (even when using the port key).  Air sampling found levels of anesthetic gases to be as high as 31 ppm when opening a bottle of isoflurane and as high as 8 ppm when using a fill key to fill a vaporizor.  Risk Management & Safety recommend the use of fume hoods for animal surgery whenever possible, provide the lowest risk of anesthetic gas exposure to the laboratory worker.

Backdraft Tables

When re-designing an animal surgery suite, backdraft tables are another option that provides protection to laboratory workers, without the barrier of a fume hood sash.  Backdraft tables pull air away from the worker's breathing zone through slots at the back of the table and is exhausted through the building's ventilation system.  There are backdraft tables that are specifically designed for animal surgery.

Downdraft Table (large and small)

Downdraft tables may be another local exhaust ventilation alternative.  However, the use of warming pads during surgery made reduce the effectiveness of large downdraft tables.  Downdraft tables pull air from above the worker and exhaust the air below the table's work surface.  Placing diapers, warming pads, and other solid items on the work surface will reduce the effectiveness of the table.

Small downdraft work stations are specifically designed for surgery on small animals such as mice and rats.  These work stations have incorporated the necessary warming pads, while still providing downdraft exhaust to pull waste anesthetic gases away from the researcher's breathing zone.

Slot ventilation

Slot ventilation is similar to a backdraft table, but can often be designed and installed by a HVAC company in an existing lab space, rather than purchasing a unit with table included. 


Snorkel ventilation is a round piece of ducting that can be moved as close as possible to a surgerical area.  These can also be designed and installed by a HVAC company into an existing lab space.  However, it is often difficult to get snorkels close enough to adequately remove all waste anesthetic gas, resulting in some exposure to the worker, depending on how close the snorkel is to the animal nose cone. 

Waste Gas Scavenging (when anesthetic gas use cannot be completed using local ventilation)

Whenever possible, surgeries should be completed in a fume hood, on a downdraft table, with backdraft ventilation, or other localized exhaust ventilation.  When connecting into local ventilation is not possible, the following solutions may be utilized.

Active Systems - Actively extracts waste gas to an exhaust or chacoal filter protected vacuum system and discharges it to a safe outdoor location. This is the next best method when localized ventilation is not possible.  Be aware that some waste anesthetic gas may desorb off the charcoal filter.  In one test, we found levels on average of isoflurane 1.2 ppm desorbing from the filter.  After surgery is complete, active systems utilizing charcoal filters should be placed in a fume hood, on a downdraft table or backdraft table so that waste anesthetic gases that desorb can be captured. 

Combination Passive/Active Systems - Collects waste gas which is pushed out of anesthesia system and actively pushes it to a safe outdoor location.

Passive System - Charcoal canisters absorb waste gas which is pushed out of the anesthesia system.  Weigh canisters periodically and dispose as hazardous waste when sorbent it full.  Immediately after each use, charcoal filters should be placed in a fume hood, as some waste gas may desorb from the filters.  Risk Management and Safety does not recommend the use of passive systems. 

Vaporizer Filling

The best method to reduce exposure to isoflurane while filling the vaporizer is to fill in a fume hood or over a downdraft or backdraft table.

When possible, have the vaporizor modified to use an anesthetic key filler (example on near right).  Connect the key to the isoflurane container in a fume hood.

If the use of an anesthetic key filler is not possible, use an anti-spill adapter (example on far right).

Induction Chamber

The highest exposure during surgery has been found when opening the induction chamber. Reducing your exposure during this step will greatly reduce your overall exposure.

Whenever possible, induce the rodent in an induction chamber inside a fume hood, on backdraft table, or adjacent to slot ventilation.

Alternately, use a gasketed chamber with exhaust port to scavenge waste gas and flush isoflurane from chamber with oxygen before opening. When sampling was conducted, we found the average concentration of isoflurane released from the induction chamber when opened was over the 2.0 ppm REL. 

Always turn off the anesthetic gas before opening the induction chamber.  Another solution is to utilize an induction chamber with active exhaust over the box opening that is designed to exhaust waste gas upon opening the chamber.

Anesthesia Machine Use

Researchers are provided the most protection when the anesthesia machine is used in a fume hood or on a downdraft or backdraft table.

Use commercially available anesthesia system interfaces or custom interfaces to collect waste gases at their source.

Regularly leak test the chamber, system, interfaces, and charcoal canister using a refrigerant leak detector.
If you smell isoflurane or the detector responds, exposures need to be better controlled.

Nose Cone

Nose cones should be chosen based on the size of the animal to be anesthetized.  Do not use a nose cone that is too large or too small for the animal. 

A good nose cone option is one with a diaphragm that can provide a seal around the nose of the animal.  Nose cones that allow for waste gas to be exhausted are the best method of reducing exposure to waste gas. 


Anyone using anesthetic gases for animal surgery, euthanasia, or perfusions must be trained in the proper procedure and safe use of the equipment prior to completing the procedure on their own.  Each lab is responsible for conducting this lab-specific training and documenting the training in their Lab Safety Notebook.