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

Hazards of Isoflurane

Health effects from a short-term exposure to an anesthetic gas may include any of the following:

  • Irritation to the eyes, skin or respiratory tract;
  • Cough or sore throat;
  • Headache;
  • Drowsiness or dizziness;
  • Asphyxia;
  • Unconsciousness. 

The health effects from long-term exposure to anesthetic gases are largely unknown. Halogenated anesthetics, in particular, have been associated with reproductive problems in women and developmental defects in their offspring.

Exposure Limit

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, for halogenated anesthetics. At that time, isoflurane use was not in widespread use. 

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

Environmental Health & Safety is available to conduct a hazard assessment of anesthetic gas use in surgery suites and/or lab spaces. EHS can also provide exposure monitoring, using sampling badges. EHS will make recommendations to help eliminate or reduce exposure. If you would like to talk to someone regarding anesthetic gas use in your lab or have exposure monitoring conducted, please contact safety@uvm.edu.

Pregnant Workers

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

General Room Ventilation

Animal surgeries, euthanasia, and perfusions must be performed in a lab with, at a minimum, general room ventilation that includes a supply and exhaust.  Labs typically are designed to have 8-12 fresh air changes per hour (ACH). Labs are designed to be negative (in air pressure) to the hallway. Animal surgery areas should be designed to be negative to adjacent areas.  It is recommended that animal surgery suites have higher air changes per hour than a typical lab.

Engineering Controls Required

Whenever possible, anesthetic gas use should be conducted in a lab area with, ata minimum, local ventilation. Most labs have a chemical fume hood that can be used to eliminate the risk of a user's exposure to an anesthetic gas during induction, surgery, and animal recovery.

Chemical Fume Hoods

Whenever possible, a chemical fume hood should be used to do the following:

  • When opening a bottle of anesthetic,
  • When attaching a fill key to a bottle, and
  • When filling the vaporizer (even when using the port key). 

Air sampling conducted 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.  Environmental Health & Safety recommends the use of a chemical fume hood for animal surgery, whenever possible, to provide the lowest risk of anesthetic gas exposure to a user.

Backdraft Tables

When designing or re-designing an animal surgery suite, backdraft tables are a great option to provide protection to users, without the barrier of a fume hood sash.  Backdraft tables pull air away from the user's breathing zone through vented slots at the back of the table. Air is then exhausted through the building's ventilation system. There are existing backdraft tables that are specifically designed for animal surgery.

Downdraft Table (large and small)

Downdraft tables are another local exhaust ventilation alternative. It is best to use a downdrfat table that also has backdraft ventilation.  However, the use of warming pads during surgery made reduce the effectiveness of large downdraft tables.  Downdraft tables pull air from the surface of the table downward, through holes in the table, and exhaust the dirty air below the table's work surface into a filtered unit. Placing diapers, warming pads, and other solid items on the work surface will reduce the effectiveness of this type of table.

Some small downdraft work stations are specifically designed for conducting surgery on small animals, such as mice and rats. These types of 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

A snorkel is a round piece of ductwork with a flange on the end that can be moved as close as possible to a anesthetic surgical area. Snorkels can be designed and installed by a local HVAC company and installed into an existing lab space. It can often be difficult to get a snorkel close enough to adequately remove all waste anesthetic gas, resulting in some exposure to the user, depending on how close the snorkel is to the animal nose cone. Have EHS conduct an assessment before use to ensure a potential exposure is eliminated or reduced.

Waste Gas Scavenging (when anesthetic gas use cannot be conducted using a chemical fume hood or local ventilation)

Whenever possible, surgeries should be completed in a chemical fume hood or by using a downdraft table with backdraft ventilation, or some another type of localized exhaust ventilation.  When connecting into local ventilation is not possible, the following solutions may be utilized.

Active Systems

Active systems actively extract waste anesthetic gas into an exhaust or charcoal filter-protected vacuum system and discharges it to a safe outdoor location.  This is the next best method only when localized ventilation is not possibleNOTE: Some waste anesthetic gas may desorb off of the charcoal filter.  In one test, levels of isoflurane, on average, found that 1.2 ppm desorbed from the charcoal filter.  After surgery is complete, active systems utilizing charcoal filters should be placed in a chemical fume hood, on a downdraft table or backdraft table so that waste anesthetic gases that desorb can be captured and exhausted properly.

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

In a passive system, charcoal canisters absorb waste gas which is pushed out of the anesthesia system.  Weigh canisters periodically and dispose of as laboratory waste when the sorbent is full. Immediately after each use, charcoal filters should be placed in a chemical fume hood to safely exhaust any waste gas that may desorb from the filters.  EHS 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.  Connect the key to the isoflurane container in a fume hood.

If the use of an anesthetic key filler is not possible, use an anesthetic anti-spill adapter. 

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 chemical fume hood or on top of a downdraft or backdraft table. Commercially available anesthesia systems interface with 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.