Capnogram/CO2 Waveform Interpretation

RE: Capnogram/CO2 Waveform Interpretation

Susanna Taylor — Mon, 01 Jul 2019 13:35:57 GMT

Great to hear you have a capnograph, and even more so that you are looking at it and thinking about it.

Firstly, just be sure you are looking at a shark fin, and not a 'hill shaped' graph. The latter is quite common in cats because of a dilution effect of the sample flow compared to the MV (assuming you have side stream). With a hill shape, you cannot get rid of it in cats, so just consider that ETCO2 is actually a little higher. In dogs it usually means a leak around the cuff, or too high FGF.

Assuming it is a shark fin, I agree with the above info. Sometimes i have seen it where the tube is rotated so the end is against the side of the trachea, instead of facing the lumen. Particularly if there is no Murphy's eye in the tube. A gentle rotation of the tube can sort it. If I hear gurgles from mucus I would ask VS if we can suction or ideally reintubate. I have seen some just give a few IPPV instead to clear it (but where does the mucus go then...)

Overall, consider a) is it increasing ETCO2 and b) is respiratory (expiratory) effort looking particularly increased? If neither, I would be happy to consider it a 'report and keep an eye on it situation'

Keep up the great work

RE: Capnogram/CO2 Waveform Interpretation

Claire Coulthard RVN — Mon, 01 Jul 2019 11:05:42 GMT

lou the vetnurse on facebook has a very handy pocket sized cheat sheet for capnography too

RE: Capnogram/CO2 Waveform Interpretation

James Colver Cert. Ed, RVN — Mon, 01 Jul 2019 09:57:32 GMT

Yes you can get similar waveforms with asthma and other restrictive airway diseases like pulmonary fibrosis ('Westie Lung') - if there's any doubt with the tube personally I would like to get it out and check/replace it - what was the bag doing?

RE: Capnogram/CO2 Waveform Interpretation

Alice Weaver — Mon, 01 Jul 2019 08:15:36 GMT

Thanks. I found a good handbook here: http://www.oem.respironics.com/wp/CapnographyReferenceHandbook_OEM1220A.pdf

What I’d like to know is what to do if you suspect ET tube obstruction during an anaesthetic. Do you remove the tube to check it?

Last week we had a 21 year old cat with unknown history under anaesthetic. Clients didn’t have a huge amount of money so we weren’t able to do pre op bloods etc. Anaesthetic was delightfully smooth! However he did have a shark fin waveform. I couldn’t hear any rattling or anything. I wasn’t monitoring the anaesthetic and was called away so didnt see him extubated and didn’t think to check it afterwards. Could the waveform in this instance be asthma? Or something to do with the patient’s age?

thanks!

RE: Capnogram/CO2 Waveform Interpretation

James Colver Cert. Ed, RVN — Sun, 30 Jun 2019 19:33:15 GMT

Hi! You might find these helpful -

https://www.smiths-medical.com/company-information/training-and-education/capnography

https://www.capnography.com/

And yes, slanted wave forms can indicate resistance like tube goobies - ideally you should see a nice 'square' ish trace. Sometimes a trace of little triangular waves indicates gas flowing around the ETT and the need for a bit more inflation of the cuff. The second website has massive banks of waveform examples to check out :)