Inhalation Anesthesia Machine/Vaporizer/Waste Gas Maintenance

IACUC Policy: 049-05, Effective Date: 08/16/2013, Last Revision: 03/17/2023

Overview/Purpose

To ensure animal safety and reduce risk of anesthetic gas exposure to animals and personnel, proper maintenance of anesthesia equipment, appropriate waste scavenging systems, and safe administration techniques must be employed. Training is available, free of charge, through University Laboratory Animal Resources (ULAR).

The purpose of this policy is to outline the required preventative maintenance and performance evaluations for anesthetic machines used for animal research on campus.

Definition

• Anesthesia machine: the entire piece of equipment that is used to deliver precise amounts of inhaled anesthetic gas and/or a carrier gas (usually air, O2 or CO2, alone or in a mix). It consists of multiple parts (precision vaporizer, carrier gas regulators, flow meters, delivery/breathing circuits and scavenge systems and possibly a rebreathing reservoir (bag).
• Breathing circuit: the tubing that delivers the fresh gas/anesthetic gas mixture from the machine to the patient.
• Induction chamber: a transparent box or container that animals can be placed within to induce anesthesia by enveloping the animal with the anesthetic gas. Such chambers should be placed inside of a biosafety cabinet (BSC) or fume hood if not connected to an active scavenge system to draw off excess gas.
• Precision vaporizer: a component of the anesthesia machine used to hold and deliver the volatile anesthetic gas.
• Scavenge systems: these systems remove halogenated waste gas from the anesthetic system so they do not return to the patient or increase exposure to the personnel.
  • Active system: incorporates a vacuum to pull off waste gas.
  • Passive system: utilizes the assumption that anesthetic gases are heavier than air. Passive flow is used to carry the waste gas through a charcoal canister which can absorb the waste gas. E.g. F/AIR, VaporGuard
• Vaporizer calibration: a process of taking apart the precision vaporizer, cleaning the components and replacing worn gaskets and verifying gas outputs with a refractometer. Such an evaluation must be performed by a qualified vendor off-site (i.e. Patterson and Henry Schein).
• Vaporizer verification: This is a process of verifying the percentage of volatile gas that the vaporizer puts out at each setting. At any time, if the vaporizer falls outside of a 20% range it must be taken out of service and sent out for calibration.

Requirements

• Performance evaluation: before each use the entire machine must be visually checked by the operator for proper function and integrity. It is recommended a checklist (see appendix below) be available at the machine level but not required.
  • All tubing must be connected and free from leaks and kinks including breathing tubing/circuits and scavenge tubing.
  • Breathing bags (if used) must be intact and free from cracks.
  • The carrier gas tanks must fit snugly onto the regulator yoke with no leaks and have sufficient levels for the duration of the procedure.
  • A scavenge system must be in place and functioning properly. A passive system requires a record of the time or weight of the canister before each use to identify when it needs to be replaced. All exhaust holes on the canister must be unobstructed. When using an active system, ensure that the vacuum is turned on and working at an appropriate flow.
• Personnel must take all measures to avoid breathing in anesthetic gases.
  • Induction chambers should be connected to an active scavenge system or used inside of a BSC/Fume hood.
  • Nosecones must fit snugly to avoid the potential for leakage of gas around the nose and work should be done inside a BSC/Fume hood.
  • If using an endotracheal tube, ideally they should be cuffed, but if no cuff is available then ensure the proper size is being used to acquire a snug fit.
• Vaporizers must be verified every three years and calibration based on performance (>20% variation). Investigative staff are responsible for ensuring appropriate validation and calibration of all investigator owned machines. Requests for validation can be made through ULAR at https://research.osu.edu/research-responsibilities-and-compliance/animal-care-and-use/diem-rates-and-fees#SurgicalandTechnicalServiceFees

Additional Information/Guidance

Anesthesia Machine Checklist

1. Inhalant anesthetic level - (i.e. Isoflurane) sufficient for the duration of the procedure
2. The carrier gas tank(s) - must fit snugly onto the regular yoke with no leaks and should have sufficient levels for the duration of the procedure. (A back-up "FULL" tank is highly recommended)
3. Inspect breathing tubing/circuits - free of cracks and holes
4. Inspect breathing bags (if used) - intact and free from cracks
5. Inspect scavenge system - tubing should be free of cracks and holes.
   1. Passive System
      1. Exhaust holes on the canister are unobstructed
      2. Canister weight has been documented
      3. Biosfaety cabinet/fume hood is turned on and ready
   2. Active System
      1. Ensure that the vacuum is turned on and working at an appropriate flow