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Anesthesia Machine Basics

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Megan Brashear, CVT, VTS(ECC), explains the different parts to the anesthesia machine. She covers proper anesthetic circuit choice, appropriate oxygen flow rates, correct reservoir bag sizing, and pop-off valve safety.

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Megan Brashear's picture
Megan Brashear


Enrolled: 07/2011

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Chris Carrasco's picture

I have noticed a lot of the technicians I work with use the O2 flush valve frequently when inducing in order to give the patients a breath if their ETCO2 is going up; is this routine or should this be avoided?

Megan Brashear's picture

Chris, using the flush valve when inducing is okay (provided the pressure manometer is monitored) but it is giving the patient pure 02, no gas anesthesia. They then have to work to saturate the breathing circuit with that inhaled gas to maintain anesthesia. If the patient has increased ETC02 (which is common during induction due to relaxation and drugs used) they should simply give the patient a couple breaths using the reservoir bag. There is no advantage to using the flush valve in that particular situation unless they want the patient to not be breathing the gas anesthetic.

Stephanie  Cowan 's picture

Megan, what is your protocol for disinfecting the anesthesia circuits? We are taking a look at this in our ICU and are considering our options. Suggestions from staff include single use, disposable anesthesia circuits (doable from $ perspective if cost of circuits are directly incorporated with sx/anes link, but inventory storage nightmare); and soaking circuits and reservoir bags after each use. We have been using a dilute kennel kare solution but I am wondering if there are options that make more sense.

Megan Brashear's picture

We have about 4-5 circuits of each size hanging at the ready and we will reuse the circuits until there is a crack or leak. We run them through with hot water and hang them to dry after use but do not use chemicals. If we are performing anesthesia on a known pneumonia patient or something respiratory infectious we will trash the circuit after use. We will clean the reservior bags with a mild detergent and hot water, an anti-viral if we need to, but it's safer to dispose of those as well if you're getting to the point of harsh chemicals.

Cheri White's picture

How di you get your bags to dry completely? With them collapsing it doesn't seem possible. How often do you clean the bags?

Jenna Martin's picture

Wow there is a lot to remember! Do techs have to have the math memorized? I better start writing this stuff down.

Kristi McKenna's picture

Megan, I have been having a discussion with a colleague about inhalant gas and O2 flow rates. I was always told that O2 is a carrier for inhalant gas. If I have my vaporizer set for 1% and my O2 flow meter on 4L, will this make my patient deep? I always thought that my patient's "deepness" was directly related to my vaporizer setting.

Megan Brashear's picture

Kristi, the higher your oxygen flow rate, the quicker you will saturate your anesthetic circuit with gas therefore getting your patient to that anesthetic depth more quickly. For example, if you induce anesthesia with propofol which is quickly metabolized, if you increase your oxygen flow rate you will get your patient deep on gas anesthetic more quickly. They will still only get as deep as your vaporizer setting, but the oxygen rate will increase the speed at which they reach that depth. If your patient gets light in the middle of the procedure and you need to turn up the gas anethetic, if you also increase your oxygen flow rate your patient will reach that deeper plane of anesthesia more quickly. You are correct, anesthetic depth is tied to your vaporizer setting.

Caroline Tanner's picture

For instance if you have a 9.5lb cat which is equivalent to 4.3kgs the flow rate should be anywhere between 107-215mls/min. Would this mean you can set your flow meter anywhere between 1 and 2? That would be big difference. How can the range be so vast?

Elizabeth Moring's picture

Hello, I am wondering how do you check the integrity of the unidirectional valves?

James Reid's picture

Hello Elizabeth,

Thanks for your comment! To check the integrity of the unidirectional valves you would simply visualize each valve opening and closing with the corresponding breath. When the patient is exhaling the exhalation valve should open and close easily. The same is true for the inhalation valve. You can also check the integrity of the valves by attaching a breathing tube to each valve and attempt to move air the opposite direction of the intended valve. For example, try blowing into the inhalation valve. If it opens then there is a problem and you should have the machine serviced. (Also, make sure you don't inhale from the inhalation valve) A common problem we see is when there is a considerable amount of condensation building up and the valves can get sticky. Dust from the Co2 granules building up can also cause problems with the valves. I have personally witnessed granules building up to the point of obstructing the valve from closing. You should be checking the valves at least daily and wiping them clean when necessary and in accordance with your practice's maintenance schedule. I hope this helps answer your question. Please feel free to ask more questions!