ETCO2 questions

[vc85]

I have a hopefully quick question about ETCO2 values.

If the person has ETCO2 values above the normal it is said that they are retaining CO2. But if a slip stream ETCO2 monitor tests exhaled air shouldn't retaining give a low number and someone who is acidotic have a high number?

 

[DesertMedic66]

I have a hopefully quick question about ETCO2 values.

If the person has ETCO2 values above the normal it is said that they are retaining CO2. But if a slip stream ETCO2 monitor tests exhaled air shouldn't retaining give a low number and someone who is acidotic have a high number?

There is more CO2 in their body for whatever reason. Since there is more CO2 they have a higher reading because they have more to blow off.

 

[vc85]

Thanks.

 

[VentMonkey]

If the person has ETCO2 values above the normal it is said that they are retaining CO2.

Anything that would cause an increase in CO2 such as COPD, and asthmatic patients, or hypo-ventilatory patients (e.g., narcotic OD’s) they retain CO2, and would have a higher than average (above 45 cmH2O).

The reverse is true regarding respiratory alkalosis, and it’s causes. You can do that research on your own.

But if a slip stream ETCO2 monitor tests exhaled air

ETCO2 monitoring is done at the end of the expiratory plateau, or the end of exhalation. It’s one of many diagnostic tools, albeit a valuable one.

The measured value dictates the patients ventilatory status, and in turn, the valued number and whether or not it may, in fact, be a contributing factor to such things as respiratory acidosis vs. alkalosis.

 

[StCEMT]

This would be a good in depth refresher topic to do. I remember my OMD went over this with us before we got cleared and discussed us using it for things like hemorrhage, DKA, sepsis, and other conditions that aren't caused by a respiratory problem.

 

[VentMonkey]

...using it for things like hemorrhage, DKA, sepsis, and other conditions that aren't caused by a respiratory problem.

Ok, so what’s it clinical significance in the listed pathologies? And what exactly would you expect to see.

I ask that the vets try and refrain for a bit.

 

[StCEMT]

Ok, so what’s it clinical significance in the listed pathologies? And what exactly would you expect to see.

I ask that the vets try and refrain for a bit.

I guess really I should go broader and say significant blunt trauma, because we were taught that it is also helpful with a pneumothorax and cardiac tamponade as well. With such things I would expect a decrease in the waveform size. 2/3 don't change what I will do, but it would still be a pertinent assessment finding to pass to the ED staff. In a pneumothorax it would be a way to monitor the effect of our treatment and if there is a recurring gradual decline again. For trauma though, it gives me a way to gauge if there is some compromise to perfusion.

DKA just to see if they are compensating for a metabolic acidosis or have they not reached that point yet. Granted, the last DKA pt definitely registered sick in my head while the last hyperglycemic pt that met DKA levels was asymptomatic. Low EtCO2. My treatment plan may be limited regardless, but I like it for the same reason as above, it gives the ED staff a better picture.

Sepsis, also running along the same gist. Metabolic acidosis compensation causing a low EtCO2. Recently was told I was picking up a septic patient with a UTI. They met 1 SIRS criteria if I remember right and that was her temp. Everything else I check was normal, EtCO2 included, so this lady was early on the sliding scale to me of the sepsis progression.

 

[E tank]

But understand that a "CO2 retainer", whether chronic or acute, is doing just that and the ETCO2 will be significantly lower than the patients PaCO2. Whether an acute asthma attack or COPD, the CO2 isn't being eliminated via exhalation because of obstructed airways. Their ETCO2 could be completely normal.

So I think the OP is on to something when they note that the number we see is low relative to the actual arterial CO2. Whether the patient has an acidemia or acidosis is another question entirely and that depends on the degree of compensation he or she is capable of.

 

[Carlos Danger]

I have a hopefully quick question about ETCO2 values.

If the person has ETCO2 values above the normal it is said that they are retaining CO2. But if a slip stream ETCO2 monitor tests exhaled air shouldn't retaining give a low number and someone who is acidotic have a high number?

In COPD, changes in the alveoli make gas exchange less efficient, so it is harder for C02 to diffuse from the blood through the alveoli into the expired gas. Because of this, higher than normal levels of C02 build up in the blood and this is why they are referred to as "retaining" C02. The EtC02 may be normal, a little high, or even a little low but the key point is that it is less than the blood (Pac02) levels.

 

[vc85]

Thanks everyone. I actually saw this in regards to sepsis and was wondering if the lactic acid builds up why does the ETCO2 fall.

Now I realize that it is actually the compensation that causes it to fall, and presumably when the body can no longer compensate the ETCO2 will rise but not as much as the arterial PaCO2

 

[E tank]

Thanks everyone. I actually saw this in regards to sepsis and was wondering if the lactic acid builds up why does the ETCO2 fall.

Now I realize that it is actually the compensation that causes it to fall, and presumably when the body can no longer compensate the ETCO2 will rise but not as much as the arterial PaCO2

Well, there is another element in sepsis (or trauma) that could cause the ETCO2 value to fall, and that is shock, or a fall in cardiac output. If the cardiac output falls, there is less blood and therefore less CO2 moving through the lungs and so less CO2 will meet the sensor in the end tidal monitor....lower ETCO2 value.

 

[vc85]

Would it be right to say that differentiating between those scenarios would be based off of the patients prssentation? I.e. Okay BP and Mental Status is probably compensation

 

[ThadeusJ]

Many years ago in the early days of EtCO2 monitoring, I had a vented bad asthmatic/nut allergy and after a few hours of venting we watched as the EtCO2 gradually dropped into normal levels. That being said, her BP, HR and other factors were becoming progressively worse. What we realized was that her airway was once again closing up and therefore the EtCO2 reading was being compromised (waveforms weren't all that accurate with this equipment on this patient). This was an excellent lesson in analyzing the source of your information and not just relying on the numbers you were given.

You should always see a delta between the PaCO2 and the EtCO2 because of the gradient necessary for diffusion to occur.

 

[E tank]

Many years ago in the early days of EtCO2 monitoring, I had a vented bad asthmatic/nut allergy and after a few hours of venting we watched as the EtCO2 gradually dropped into normal levels. That being said, her BP, HR and other factors were becoming progressively worse. What we realized was that her airway was once again closing up and therefore the EtCO2 reading was being compromised (waveforms weren't all that accurate with this equipment on this patient). This was an excellent lesson in analyzing the source of your information and not just relying on the numbers you were given.

You should always see a delta between the PaCO2 and the EtCO2 because of the gradient necessary for diffusion to occur.

Dynamic hyperinflation (breath stacking)?

 

[ThadeusJ]

Dynamic hyperinflation (breath stacking)?

There were definite breath sounds at end-exhalation indicating that there was still more air to be moved out but we tried to get out as much as we could. It was a few years ago and the machines could only do so much but we were able to help her out without causing damage to the airways. To compound the issue, she was pretty much peripherally shut down and ABG's were very hard to get to correlate to the EtCO2.

 

[NPO]

New question, sorry to hijack...
The other day I had a post-arrest patient who initially had an ETCO2 of about 9 (intra-arrest) which was especially concerning given the relative short downtime and the use of the Lucas 2, which generally produces ROSC-level ETCO2 readings...

Once we achieved ROSC the patient had a peak ETCO2 of about 40, which slowly dwindled to 25. The patient had a bounding pulse, HR of about 90, and blood pressures in the 150/100s. I ruled out decreased cardiac output as a cause of the decreasing ETCO2. The patient was mechanically ventilated, so I don't think hyperventilation was the cause either... (In case it's relevant, vent settings were SIMV, VT400, PEEP 7, Rate of 10).

Any insight to why her CO2 was falling, and what to do, if anything, to get it back to the 30s?

 

[TXmed]

Just because the patient had a SBP does not mean they had good right-left cardiac blood flow. Also possible PE.

 

[CWATT]

@NPO - what was the pt’s body weight and height (to calc Ideal Body Weight)?

 

[VFlutter]

Pressure does not equal flow. People can have a normal/high pressure (high afterload) and minimal forward flow (Cardiac output).

Or any number of lung pathologies.

Is an ETC02 of 25 necessarily bad in a post arrest patient? You should get an initial increase in ETC02 with ROSC since perfusion has now improved however once that has passed you still may have an underlying metabolic acidosis.

 

[E tank]

New question, sorry to hijack...
The other day I had a post-arrest patient who initially had an ETCO2 of about 9 (intra-arrest) which was especially concerning given the relative short downtime and the use of the Lucas 2, which generally produces ROSC-level ETCO2 readings...

Once we achieved ROSC the patient had a peak ETCO2 of about 40, which slowly dwindled to 25. The patient had a bounding pulse, HR of about 90, and blood pressures in the 150/100s. I ruled out decreased cardiac output as a cause of the decreasing ETCO2. The patient was mechanically ventilated, so I don't think hyperventilation was the cause either... (In case it's relevant, vent settings were SIMV, VT400, PEEP 7, Rate of 10).

Any insight to why her CO2 was falling, and what to do, if anything, to get it back to the 30s?

I'll chime in...All things equal, her ETCO2 trend would not concern me in the least given that she sounds like a bona fide save with plenty of cardiac output and I'm assuming good oxygenation because you didn't say anything about that. If I had to pick something to be concerned about it would be that HR and diastolic pressure, but that would probably be temporary given the circumstances.

If the BS's, SaO2 and perfusion is OK, I'd note it but not worry about it. I will say the most common reason for a lower ETCO2 without perfusion problems or obstructive lung dz is hyperventilation, like you pointed out, so, I got nothing for ya.