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Tiny Talk - ETCO2 in Anesthesia

Views: 18484 - Comments: 12

In this Tiny Talk, Megan Brashear, CVT, VTS (ECC), discusses end tidal CO2 and why it is important to monitor in anesthetized patients. Understanding what that value means to the patient and tips for keeping it within the normal range are discussed. 

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Megan Brashear's picture
Megan Brashear


Enrolled: 07/2011

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dlManager's picture

Just looking at the comment functionality! It's awesome

Bertsie Cantu's picture

What about the inhaled CO2 levels? Most of the times I've seen a value of 0 but occasionally i'll get values ranging from 2-9.

Jessica Waters-Miller's picture

Hi Bertsie,

Thank you for the question! You are correct that is a broad range. This elevated number or the inhaled ETCO2 can be due to hyperventilation where they are not taking proper breaths (making small short ones) so the air exchange is not complete. Another common reason can be because of an anesthetic machine malfunction; for example, the exhaust valve is stuck causing a backup of ETCO2 or it could be due to the baralyme needing to be replaced. It is also important to adjust the oxygen flow rate to the patient's needs. If it continues to trend upward I would disconnect the patient and use a different machine.
There can be many factors to an increase in inhaled ETCO2 but knowing more about the case would be important and what equipment you use. I hope this makes sense and helps a little. If you have more specific questions please leave another comment.

Krista Frye's picture

Do you guys ever have an issue with a machine malfunction? I have had several instances where my EtCO2 is either really high or really low and the mapping isn't consistent with the breaths the patient is taking. I have tried several different anesthesia related changes and even when i breathe for the patient it wont pick it up. I'm not sure if there's some sort of maintenance I'm missing or anyone else experiences this?

Rachel Medo's picture

Hi Krista,

Can you let me know what brand of machine or type of equipment you are using? I've passed your question along to a few of our staff at DoveLewis.

Krista Frye's picture

Thanks for getting back to me! its the surgivet advisor 3

Rachel Medo's picture

Hi Krista,

I checked in with our Medical Equipment Specialist about your question and have put her response below.

"We use the SurgiVet Advisor 4 here at DoveLewis. It sounds like your machine needs to be calibrated to hopefully address the problems your having. I believe the SurgiVet (Smiths Medical product) is supposed to be serviced once yearly by the manufacturer.

There is also a calibration kit specifically for the ETCO2 that can be purchased through Smiths Medical. I believe the recommendation is to have it calibrated every 3 months or so. We employ Patterson Veterinary to do monthly equipment maintenance at our hospital, and their technician checks our SurgiVet monitors every month, calibrating them if necessary.

If you would like to purchase the calibration kit from Smiths Medical or get advice, I highly recommend speaking directly with one of their technicians (Tel: 888-745-6562, then pick option 2). Their techs are usually very helpful over the phone."

Hopefully that at least gives you a starting place! Please let me know if I can answer any additional questions.

Janice Bergeron's picture

I wish you were our clinical instructor! Starting my second year. Have to catch up on last semester clinicals due to Covid shutdown.

Dakota Sekella's picture

Why would severe hypothermia cause hypocapnia if hypocapnia is caused by hyperventilation? Wouldn't hypothermia cause hyperventilation and therefore hypercapnia?

James Reid's picture

Hello Dakota,

Thanks for the great question! In the video Megan states that "severe" hypothermia can lead to hypocapnia because "everything" slows down. My take from what she is referring to would be that cellular metabolism has slowed down significantly enough that the gas exchange is not happening as it should. Therefore the ETCO2 will read as being low (hypocapnia). I'm not sure how I would correlate hypothermia with hyperventilation in this case. Generally speaking hyperventilation can cause hypothermia. I hope this helps answer your question.

Jessica Salazar's picture

Hello, great video. I did have a question. On the 2020 AHAA anesthesia guidelines it states that 33-45 is the normal in awake patients. However, for anesthetized it is 33-55mmHg. It states to give PPV only if above 60mmHg. What are your thoughts on this?

James Reid's picture

Hello Jessica,
Thank you for the question. I did a little research and I'll paste the sections from the 2020 AHAA guidelines. "ETCO2 is about 35–45 mm Hg in awake patients and about 40– 50 (up to 55) mm Hg in patients in an appropriate surgical plane of anesthesia." I'm a little confused by this because in order to get a proper accurate ETCO2 reading the patient would need to be anesthetized and intubated. It might be possible to get a reading from a nasal cannula or a tight fitting breathing cone but that isn’t something we routinely do. Perhaps they are referring to PaCO2 (arterial blood gas)? For our purposes at Dove Lewis we generally use the range of 35-45mm Hg. Below 35mm Hg is considered hyperventilation and above 45mm Hg is considered hypoventilation. "Initiate PPV if ETCO2 is >60 mm Hg (hypercapnia)." Generally speaking this is correct, and hypercapnia is one of the triggers for us to consider mechanical ventilation in our non-surgical respiratory patients. However, there may be times when you would need the patient to have a lower ETCO2. For example, in patients with brain injury, higher ETCO2 readings such as 60mm Hg can cause an increase of intracranial pressure (ICP) and therefore you would need to maintain a lower ETCO2 closer to 35mm Hg. This could be achieved by positive pressure ventilation. On the opposite end of the spectrum, permissive hypercapnia is a ventilation strategy that allows for much higher than normal ETCO2 in order to pursue a more lung protective ventilation strategy. We also use mechanical PPV (ventilators) for most of our major surgeries regardless of their ETCO2. I feel it's important to stay away from absolutes in regards to anesthesia because your targets and strategies should be tailored to your patient’s needs. A patient with normal, healthy lungs that exchange oxygen well will be better able to tolerate the hypoventilation that leads to high ETCO2 levels than a patient with abnormal lungs. Therein addition to patient variables, you will find exceptions or slight variations in target ranges depending on the reference you consult. Any target range (including our defaults) should be interpreted in light of your own patient.