The anesthesia vaporizer is a critical component of your veterinary anesthetic machine. It is very important to ensure that the appropriate percentage of anesthetic agent is being delivered. A malfunctioning vaporizer can be the cause of inappropriate depth of anesthesia (e.g., animals under anesthesia too lightly or too deeply) and may also be the reason you “lose” a patient.
Most vaporizers used today in veterinary practices are used with either Isoflurane or Sevoflurane. There are still some Halothane (Fluothane) vaporizers on the market; however, the agent is hard to find as most manufacturers have discontinued their production.
Frequency of service
You should have your veterinary anesthesia machine maintained annually. Leaks on your machine can provoke dilution of anesthetic gas and pollute your environment, not to mention the increase in your operating costs. “The fact that you have no problem keeping your animals under anesthesia does not mean that your staff is not breathing the gas all day long as well”. At the time of service, the technician should have an anesthetic agent monitor and should provide you with the readings of the vaporizer. It is important to note that these readings are only an indication of the vaporizer output at the time of inspection, it is not a calibration. Calibration of vaporizers is impossible to perform on-site as it must be done in a controlled environment. Anyone who tells you otherwise is misleading you.
Most vaporizers on the market are considered “in-spec” if the output is within +- 15% of the dial setting. If the output is beyond that, the technician will recommend changing your vaporizer with a freshly calibrated one or send your vaporizer out for recalibration.
Why can’t vaporizers be serviced on-site?
Vaporizer output is affected by the temperature of the agent. The colder the agent, the lower the vaporizer output; the hotter it gets, the higher the output. Several factors affect the temperature. The oxygen flows through the anesthesia vaporizer and cools the agent down; the room temperature affects the vaporizer temperature. The vaporizer contains a thermostat which regulates the output to compensate for these temperature variations, but it has its limits. In order to recalibrate the thermostat, it must be done in a temperature-controlled environment. Adjustments are made at precise temperatures and rechecked after a minimum of 4 hours between adjustments to confirm stability. Several subsequent identical readings are required before considering the calibration to be valid. This process may take up to 5 days. Once completed, the vaporizers are fully dried before being shipped.
If you are using Halothane, it should be fully recalibrated and overhauled annually. The agent contains a preservative (Thymol) which gradually creates deposits on all parts of the vaporizer, causing the dial to be harder to turn and intermittently affect output.
Isoflurane & Sevoflurane
Since these agents do not contain Thymol, they do not leave deposits in the vaporizer and need recalibrations less frequently. It is still necessary to have the output checked annually when verifying your anesthesia machine. An indication that your vaporizer is due for recalibration is if you find yourself routinely having to use higher or lower concentrations than you generally use. However, it is assumed that you perform daily leak checks on your anesthesia machine.
During the recalibration process, many parts require replacement. The wick assemblies, the o-rings, etc., should always be replaced. Any other worn part should also be replaced.
Before sending your vaporizer for recalibration, it must be drained of all agents. Leaving agent in the vaporizer can cause damage. Proper packaging is very important.
When you fill your vaporizer for the first time, it may seem that you are losing agent rapidly. This is normal. A cotton wick inside the vaporizer absorbs a great deal of liquid and requires 2 to 3 fillings before being fully saturated.
Need More info?
If you have any doubts or questions about your veterinary anesthetic agent vaporizer, it is important to contact a professional who will be able to evaluate the situation.