End tidal CO2 Monitoring

[Supermanwoot]

I don't think that is what she said. And you are getting further and further from diving relation.

Thats my point exactly. ETCO2 is not a valid parameter to measure for diving. It just doesn't make sense unless you are taking a patient diving who requires mechanical ventilation underwater with questionable cardiovascular function.

CO2 being exhaled (ETCO2) is a good thing. If it builds up in your exhale circuit it should get vented or scrubbed. CO2 on your inhale side is a completely different entity.


And to correct what was said by TSandM, ETCO2 does not measure your ventilation as much as perfusion, stop saying that. ETCO2 will be higher if you are perfusing more and metabolizing oxygen, but you can stop breathing and have an end tidal. Can you tell from someones ET if they have a respiratory acidosis? no you cant, you have to pull an ABG or shock panel.

edit: Somehow people are associating ETCO2 with what you are breathing in. But thats saying that better measured by a CO2 sensor before inhalation, because AFAIK even 1% Co2 can be potentially hazardous to inhale, esp at depth. But the chances that inhaling 1%CO2 would significantly affect ETCO2 is questionable at best, especially if the toxic effects slow down your circulation, causing a misleadingly normal level.

 

[TSandM]

Supermanwoot, what is your training? Some of the things you are saying are simply not correct. I am a physician with training in general surgery and critical care, who does ER work.

ETCO2 is a very good surrogate for arterial CO2, which is precisely WHY we measure it in ventilated patients. You are very correct that CO2 measurement alone does not give you the patient's acid-base status, which is the only real remaining utility of arterial blood gases. But CO2, whether in the blood or in end-tidal expired gas, does not measure perfusion. I can be underperfused and acidotic and have a normal pCO2, if I can't ventilate enough to compensate for my acidosis.

This is WAY beyond a discussion of ETCO2 on rebreathers, where perfusion and lung function are posited to be normal to begin with, and all you're doing is using CO2 measurement in the loop to advise the diver of a dangerous buildup in the blood.

 

[lemon]

There's a lot of very incorrect information in this thread from a medical perspective.

Getting back on topic - CO2 measurement would be useful to detect scrubber breakthrough. This is a feature that I would welcome if/when it becomes practical/affordable.

 

[Garth]

There's a lot of very incorrect information in this thread from a medical perspective.

Getting back on topic - CO2 measurement would be useful to detect scrubber breakthrough. This is a feature that I would welcome if/when it becomes practical/affordable.

I can agree.

 

[Cave Diver]

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The off topic tete'-a-tete' has been removed.

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[bigblue_hi]

Scrubber breakthrough does not occur quite as instantaneously as some comments in this thread may have implied.

If you have a sensor capable of reliably detecting CO2 percentages to the tenth of a percent in small amounts (e.g. 0.3%) it would be worthwhile to have in a CCR.

Breakthrough is pretty rapid, but not "in a few breaths", something like 0.5 -> 3% in ~10-15 minutes is more reasonable. Around 4-5% is when you start to see minor CO2 poisoning with >10% being a serious situation (i.e. time to get off the loop). Of course it depends on scrubber design, temperature, breathing rate.. CO2 generation rate.. yadda yadda.. but the above figures are reasonable. In some cases the rise is much slower.. i.e. 0.5% to 1% over 2 hours perhaps. Generally once it gets to around 1% it spikes pretty quickly though (10-15 mins).

The real risk of course is that people would start to dive while relying on the CO2 sensor for stretching sofnolime life.. etc..

 

[kodak88]

Lets think about it. When do you monitor ETCO2? In an intubated patient, therefore they are not breathing properly by themselves and so a ventilator is breathing for them. You don't measure ETCO2 on a person breathing on their own, nor is it a determinate for when to intubate someone.

ETCO2 is monitored closely when a patients "codes," or goes into cardiac arrest. This is a BLOOD FLOW issue. CO2 is a metabolite of cellular respiration and so it is returned VIA THE BLOOD to the lungs where it is able to be pulled off by the ventilator.

A High ETCO2 during CPR is a good thing. This means the body is getting the oxygen, using it, and returning CO2 via the blood. Its a means of measuring pulmonary perfusion, not the patients ability to breathe because we provide that for them.

If the ETCO2 is LOW, then their body is not getting the oxygen (not being perfused and not returning blood to the lungs).


So now lets apply this to scuba. Is your heart beating? Yes. Are you breathing on your own? Yes.

So why would we need to monitor ETCO2, if anything a high ETCO2 would tell us we are working hard. A low ETCO2 would be the problem, meaning you aren't getting BLOOD FLOW back to your lungs, but in that case just check your own pulse.

What I'm saying is ETCO2 is something completely different than what its being proposed for here.

Ahhh, no. Trust me on this one. Its about 60% right, but reasoning is flawed

 

[Garth]

Look up end tidal co2 in the nonintubated patient. You Will find results because end tidal co2 can be monitoring in the nonintubated person.

Is anyone listening out there?

 

[Garth]

Look up end tidal co2 in the nonintubated patient. You Will find results because end tidal co2 can be monitoring in the nonintubated person.

Is anyone listening out there?

That being said I don't see a point of this for rebreather divers. As was said before a scrubber monitor would be a nice invention.

 

[kodak88]

That being said I don't see a point of this for rebreather divers. As was said before a scrubber monitor would be a nice invention.

There are monitors, since everyone likes to use intubated patients as examples, the two main types of anesthetic scrubbers both have a blue dye that appears when the scrubber is spent.