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anesthetic gases

Anesthetic Gases

Potential workplace exposures to anesthetic gases in research lab settings occur in stand‐alone procedure rooms, veterinary and lab animal facilities. Engineering, work practice, and administrative controls that help reduce these exposures in all anesthetizing locations, are identified and discussed below.

The NIOSH REL for nitrous oxide, when nitrous oxide is used as the sole inhaled anesthetic agent, is 25 parts per million (ppm) measured as a time‐weighted average (TWA) during the period of anesthetic administration (NIOSH 1977). NIOSH also recommends 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. In 1989, the American Conference of Governmental Industrial Hygienists (ACGIH) assigned a threshold limit value‐time‐weighted average (TLV‐TWA) for nitrous oxide of 50 ppm for a normal 8‐hour workday. ACGIH TLV‐TWAs also exist for halothane and enflurane, and are 50 ppm and 75 ppm, respectively.

No anesthesia machine system is totally leak‐free (Emergency Care Research Institute 1991). Leakage may originate from both the high‐pressure and low‐pressure systems of the anesthesia or analgesia machine. The use of induction chambers and bell jars also can expose the researcher to unscavenged waste anesthetic gas (WAG).

Possible health effects of overexposure to anesthetic gas may include, but are not limited to:
•    Acute effects: Drowsiness, irritability, depression, headaches, dizziness, and nausea, as well as problems with coordination, audiovisual ability, and judgment.
•    Chronic effects: Liver and kidney disease, and adverse reproductive effects.

Work Practices

  1. Prepare for anesthetic gas use:
    • Inspect anesthesia equipment and scavenging system.
    • Verify equipment (e.g., fume hood and vaporizer) is currently certified and in proper working condition.
    • Ensure vaporizer is filled with the specific anesthetic agent for which it is designed and certified. Fill vaporizer using an anti‐spill bottle adaptor OR conduct filling in fume hood. When filling, wear chemical‐resistant gloves, a lab coat, and eye protection.
    • Check for leaks, defects, and damage in anesthesia equipment (including hoses and valves) and scavenging system by pressure testing or by running oxygen through machine and then spraying suspected leaks with soapy water or Snoop. b.
  2. Prepare charcoal canisters for use:
  •          Charcoal canisters must be weighed before and after each use to ensure they are within manufacturer’s              specified limits (e.g., <50 grams above the initial weight); record the date and weight on the canister                      and/or  user log.
  •          Confirm that the canister is correctly plugged into the breathing system. Use charcoal canisters according          to manufacturer’s recommendations.
  •          Ensure the canister holes are not obstructed. Canisters should be used upright,                                                                regardless of where gas exit holes are. For example, F/Air canister has exhaust ports at                                                  the bottom and requires a canister holder to elevate the canister above the surface of the counter,                          allowing gas to pass through unobstructed.

 

  1. Specific safe work practice for anesthetic inductions:
    • Open‐drop anesthetic procedures are not recommended but, if necessary, shall be conducted within a chemical fume hood.
    • Do not turn on the vaporizer until the animal is in the induction chamber.
    • Purge the induction chamber with oxygen for 5 to 15 seconds prior to opening the chamber and retrieving the anesthetized animal.
    • Keep the vaporizer turned off or the nosecone plugged until the animal is properly positioned in the nose cone.
    • Turn off the vaporizer or plug the nosecone before taking the animal out of the nose cone.
    • Co‐administration of anesthetic and/or analgesic agents will allow lower isoflurane usage.
    • Minimize WAG leakage from the nose cone by selecting the best‐fitting nose cone. Nose cone diaphragms are available from vendors in various sizes to optimize fit. A modified diaphragm may be made from the finger of a powder‐free nitrile surgical glove to increase the nose cone fitting. Modified nosecone with a diaphragm is recommended for the passive scavenging system only.
    • Oxygen flow rate and anesthetic concentration should be as low as possible to minimize anesthetic gas usage. This is highly variable and dependent on strain, age, sex, analgesics used, and individual animal.
    • Keep WAG capture/collection devices positioned as close as possible to potential points of release (e.g., at animal nosecone).


 

  1. Keep the researcher’s breathing zone at maximal distance away from the animal nosecone, as gas concentrations decrease rapidly with distance.
  2. Personal protective equipment

Standard PPE for isoflurane use consists of chemical‐resistant gloves, lab coats, and safety glasses. Additional PPE may be needed depending on other chemical/physical/biological agents used in the research protocol

  1. Waste Management:
    • Manage unused/expired anesthetic gases and liquids as hazardous waste: Create hazardous waste pickup tags using E‐trax.
    • Manage spent charcoal canisters as non‐hazardous waste: Seal, bag, and label canisters as “non‐hazardous waste” (include disposal date, contact name, and phone number). Request pickup of used canisters through E‐trax.
  2. Equipment Maintenance

Anesthesia machines and vaporizers are to be calibrated and certified as recommended by manufacturer (typically biannually). Contact DLAR for additional guidance.

Engineering Controls

  1. Always work in a well‐ventilated area with at least 6 room air changes per hour regardless of gas capture/scavenging methods in use. Labs on campus are designed to have air change rates of 6 or greater. If anesthetic gases are to be used outside of a lab setting, contact labsafety@uky.edu for consultation.
  2. Prior to anesthesia induction, the anesthesia machine (if used) and its components/accessories should be made ready for use. All parts of the machine should be in good working order with all accessory equipment and necessary supplies on hand. The waste gas disposal system should be connected, hoses visually inspected for obstructions or kinks, and proper operation determined. Machine fittings, inlets, connections, gaskets shall also be inspected for wear and tear. Ensure the vaporizer is properly connected and not misaligned.
  3. An appropriate anesthetic gas scavenging system is the first line of defense and the preferred method of control to protect employees from exposure to anesthetic gases. An effective anesthetic gas scavenging system traps waste gases at the site of overflow from the breathing circuit and disposes of these gases to the outside atmosphere. Removal of excess anesthetic gases from the anesthesia circuit can be accomplished by either active or passive scavenging. When a vacuum or source of negative pressure is connected to the scavenging interface, the system is described as an active system. When a vacuum or negative pressure is not used, the system is described as a passive system.  The following controls are listed in order of most effective waste gas control to less effective.
  1. Active capture/scavenging:
    1. Chemical Fume hood: Work in a CFH for best WAG capture performance.
    2.  Active scavenging devices (ducted): WAG collection devices (e.g., snorkel trunk, EVAC‐4) are recommended to be ducted to the building exhaust system. Do NOT use the house vacuum as a means of active scavenging.
    3. Active scavenging devices (ductless): Where WAG collection devices cannot be ducted to the building exhaust system, use a manufacturer recommended air cleaning extraction system with an activated charcoal adsorption unit to actively scavenge WAG. NOTE: Charcoal adsorption units CANNOT be used with nitrous oxide.
    4. Passive scavenging:
      1.  Do NOT use passive scavenging with nitrous oxide. Charcoal canisters: This method relies on positive pressure from the anesthesia machine and the anesthetized animal’s exhalation to push WAGs into gas adsorption units (i.e., canisters). Any leaks in passive scavenging systems, such as an inadequate seal on the induction chamber cover, tubing, or nose cones, can cause WAG to leak into the work area. Passive scavenging is not recommended for small animal surgery of greater than 3 hours or for stereotaxic surgery of any duration. If using passive scavenging systems, connect one charcoal canister to the animal nosecone and another to the induction chamber.

 

If options for scavenging are limited, personal respiratory protection may be necessary for researcher health protection. Contact the UK Department of Occupational Health and Safety for consultation.

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