# ETCO2 of 9



## Simusid (Jun 4, 2013)

I was on a call recently for an unresponsive female with an unknown downtime.  HX of ETOH abuse and family members stated "she was on meds for it", there was no evidence of alcohol on scene.  Nor an evidence of an overdose

She remained unresponsive, had irregular respirations at a rate of about 10, a pulse of about 120, O2 SAT of 100%.  I don't remember the BP but it was not hypotensive.   She also had some moderate irregular jerking of her right side limbs.  My partner said "drug overdose or a head bleed...lets go" and we did.  At the hospital, it was discovered (by the family) that she actually drank brake fluid.  

The thing I don't understand is that her ETCO2 was 9.  She had a perfusing rhythm and had some level of respiration (though inadequate, she ended up being tubed).  Satting 100% she was moving blood and air....why would her CO2 be only 9?   could the brake fluid interfere with that measurement?


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## NYMedic828 (Jun 4, 2013)

Ethylene glycol is highly toxic to humans if ingested. 

Was she drinking it in a suicide attempt? I can't imagine anyone drinking a substantial amount by accident...


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## ThadeusJ (Jun 4, 2013)

What was the waveform like?  It would have been interesting to see what the ABG's were so you could correlate the gradient.  How was the EtCO2 measured (prongs?).  Were they compromised with secretions?


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## Simusid (Jun 4, 2013)

ThadeusJ said:


> What was the waveform like?  It would have been interesting to see what the ABG's were so you could correlate the gradient.  How was the EtCO2 measured (prongs?).  Were they compromised with secretions?



Sorry I did not see the waveform, only the number.   I'm fairly sure there were no significant secretions.


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## fast65 (Jun 4, 2013)

I know someone asked this already, but how was the ETCO2 measured? Was it through a nasal cannula, or was it monitored after she was intubated?

If she was breathing primarily through her mouth, then you'll obviously have a skewed reading if you're using a cannula to monitor capnography. That being said, I would also like to see the ABG's.


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## Simusid (Jun 4, 2013)

fast65 said:


> I know someone asked this already, but how was the ETCO2 measured? Was it through a nasal cannula, or was it monitored after she was intubated?
> 
> If she was breathing primarily through her mouth, then you'll obviously have a skewed reading if you're using a cannula to monitor capnography. That being said, I would also like to see the ABG's.



It was measured with a NC on a lifepak 15


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## NYMedic828 (Jun 4, 2013)

Simusid said:


> It was measured with a NC on a lifepak 15



That measurement may or may not be accurate then. When she was intubated it should be re-assessed via the ET tube to see how close the numbers are.

The NC type has too many variables to be completely accurate. Anything from secretions blocking the prong to exhaled air simply coming out of the mouth vs the nose can affect the reading.

Its an extra tool its not very good for more definitive measurements. Kinda like pulseoximetry.


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## STXmedic (Jun 4, 2013)

I'm not sure what kind of EtCO2 cannulas y'all use, but the ones we use here have a piece below the nasal prongs that sits in front of the mouth and captures the air exhaled from the mouth. 
	

	
	
		
		

		
			




So depending on what type of cannula the OP uses, mouth breathing may or may not affect the end-tidal reading.


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## Tigger (Jun 4, 2013)

PoeticInjustice said:


> I'm not sure what kind of EtCO2 cannulas y'all use, but the ones we use here have a piece below the nasal prongs that sits in front of the mouth and captures the air exhaled from the mouth.
> 
> 
> 
> ...



That's what we use and unless the patient is forcibly exhaling through their mouth they are still accurate.


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## RustyShackleford (Jun 4, 2013)

We use the same type as noted above and they have always been pretty accurate when compared to in hospital/ETT readings.


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## Melclin (Jun 5, 2013)

ETCO2 is generally only considered to be a reliable indicator of PCO2 in young people who aren't super crook. Derangement of cardiac output and lung function effect it.  

Here is a nice short doc on ETCO2 with reference to V/Q.  
http://www.procamed.ch/pdf/etco2_gradient.pdf

Probably falsely low though due to some oddity of the equipment (as others have already mentioned), which would be impossible to say without 




A good resource for capnography.

http://emscapnography.blogspot.com.au/


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## jwk (Jun 6, 2013)

RustyShackleford said:


> We use the same type as noted above and they have always been pretty accurate when compared to in hospital/ETT readings.



No, they are not.  Using the numbers from any system that monitors EtCO2 from a nasal cannula is pointless.


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## Simusid (Jun 6, 2013)

So far the responses seem to be questioning that the ETCO2 measurement is wrong.   I get that, and I do not blindly treat numbers.

But my question is more about physiology I think.  Suppose hypothetically that the number was correct.  What could be going on in her body to cause this low reading?


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## ThadeusJ (Jun 6, 2013)

You have to consider what you are looking for.  Reading an airway sample of CO2 assumes a correlation with pulmonary vascular PCO2, which assumes a correlation with systemic PCO2 and cell function.  Therefore, if the machine is reading correctly, one can consider a V/Q mismatch where the CO2 in the pulmonary vasculature is higher (severe bronchoconstriction).  _If the CO2 in the pulmonary vasculature is in fact low, then there could be a issue such as shunting of the blood from the right side to the left side of the heart, bypassing the pulmonary system, in which case the systemic PCO2 is higher than the pulmonary PCO2.  An ABG would detect that as well.

If the patient is hyperventilating and the system is working properly, then the systemic PCO2 would be low as well.  I can't think of why cellular PCO2 would be high and not diffuse into the systemic bloodstream.  I suppose there could be a cataclysmic shift of the Henderson Hasselbalch equation where the PCO2 leaves the system to form bicarb, (I think that was the mechanism in the Fantastic Four when Thing was created, but I digress)._


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## 46Young (Jun 6, 2013)

A few days ago I ran a teenage girl at school for abdominal pain. When we arrived, she was hyperventilating north of 40/min. Her B/P was roughly 110/62, P 80, SpO2 100% RA per the engine crew initially. The engine crew had her on an NRB with 2lpm, presumably so that she would rebreathe her CO2. My EMT-I partner who was riding lead cranks up the O2 to 10 LPM's against my wishes. As we were transporting her to the ambulance, she hyperventilated herself into syncope. 

In the back, I remove the mask to place a Capnoline (like the one in the picture a few posts ago). My partner says to keep her on O2 because "she passed out" (facepalm by me). I tell him that I'll do 4lpm NC, but I just pretend to turn on the O2. Vitals at this time were 114/60, 80P, RR 4, BGL 92, SpO2 100% (room air again haha), ETCO2 of 9. That is what made me think of this call, the ETCO2 of 9.  The father was in the back with us, and tells us that his daughter gets panic attacks wen she's ill, because she thinks she's going to die each time (Hx of Sz only, no Sz today). My partner drops a line, and has me do a 12-lead. The 12 is unremarkable. 

Meanwhile, the pt had irregular respirations. She was apneic at one point until I shook her. My partner didn't know that I didn't use O2. She started picking up her resps. at the time I got out to drive. She was still dazed, but conscious and following commands a few minutes later at the hospital. I pulled the trends after the call. As her ETCO2 moved up, so did her respiratory rate, which was 16 upon arrival, other vitals largely unchanged. I was comfortable with ruling out a PE as a differential.

The point of all of the above is that I'm wondering if the OP's alcoholic pt also had psych issues. Is it possible that she had a panic attack moments before someone discovered her and called 911? 

Low ETCO2 values occur for several reasons. A low flow state, such as profound shock or cardiac arrest can cause low ETCO2, since that reading is dependent on blood returning to the alveoli, to exchange CO2. A PE can block blood flow to a large enough region of a lung to cause a reduced CO2 reading. A pt that is hyperventilating will naturally eliminate a lot of CO2, which puts them into respiratory alkalosis. A pt in DKA, in metabolic acidosis may compensate with hyperventilation, which eliminates CO2 with an effect much like someone having a panic attack, since the underlying problem is metabolic, not respiratory. The increased respirations will not help, just blow off CO2. 

When he pt is acidotic, it becomes increasingly difficult for O2 to bind to Hb. Reference the SpO2 dissociation curve, and how rapidly the sat drops after you turn the elbow. When the pt is alkalotic, O2 will readily bind to Hb (Bohr Affect), but the Hb will not release the O2 as readily (basically prevents O2 txp). In addition, you have the cerebral vasoconstriction. So, this is how patients get dizzy and eventually pass out from hyperventilation syndrome.

Since your patient was an alcoholic on some undisclosed meds, is it possible that underlying psych issues caused a hyperventilation episode prior to her being discovered as unconscious by the caller? Probable suicide attempt after all IMO....


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## Carlos Danger (Jun 6, 2013)

Simusid said:


> But my question is more about physiology I think.  Suppose hypothetically that the number was correct.  What could be going on in her body to cause this low reading?



Normally, Etc02 closely approximates arterial C02 tensions. So, barring equipment failure, there are only two reasons why the Etc02 would be 9:


*The patient is alkalotic*. This means the systemic pH is increased for metabolic or ventilatory (increased minute volume / "hyperventilating") reasons, which results in a corresponding decrease in the Etco2. 

Metabolic alkalosis is fairly uncommon, and I think the main toxin in brake fluid is ethylene glycol, which normally causes acidosis rather than alkalosis. 



*The patient has an increased C02 gradient* as a result of pathology. Normally, since not all the C02 in the blood diffuses across the alveolar-capillary membrane into the alveoli to be exhaled, the Pac02 is 2-5 mmHg greater than the Etc02. This is termed the "Arterial - Etc02 gradient", or P(a-et)Co2. It is analogous to the alveolar-arterial oxygen gradient (A-a gradient).  

An increased C02 gradient suggests that Co2 is not making its way from the blood into the alveoli due to low cardiac output, a problem with the alveolar-capillary membrane (pneumonia), ventilation-perfusion mismatch, or possibly some combination of the three (ARDS / ALI).


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## Handsome Robb (Jun 6, 2013)

And after that this thread can end. 

Great post! Learn something new every day.


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## 46Young (Jun 6, 2013)

Robb said:


> And after that this thread can end.
> 
> Great post! Learn something new every day.



Not yet!

In my last post, I forgot to add that hyperventilation and the resultant respiratory alkalosis also causes a reduction of available Calcium (hypocalcemia), which can cause tetany, which is where you get the painful carpal-pedal spasm.

That's all I got


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## MasterIntubator (Jun 7, 2013)

Simusid said:


> ...why would her CO2 be only 9?



Did it stay that way, or did it start to rise after 5-10 minutes?

She prob hyperventilated herself out.... takes some time to autoregulate


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## Simusid (Jun 7, 2013)

MasterIntubator said:


> Did it stay that way, or did it start to rise after 5-10 minutes?
> 
> She prob hyperventilated herself out.... takes some time to autoregulate



No she was found unconscious prior to the 911 call, and she remained unconscious throughout the whole transport.  That was probably close to 1/2 an hour from the original report.  It was an unknown, probably extended downtime.  I think the family was worried that they had not heard from her and that is what prompted the call.   The two capnography measuerments that I saw were 9 and 8 and they were probably close to 10 min apart.

I know I'm only a basic but I *seriously* doubt this was hyperventilation.  I've heard "when you hear hoofbeats, first think horses not zebras" but drinking brake fluid is probably in the zebra category.


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## MasterIntubator (Jun 7, 2013)

Ehh ehh... forgot about the OD... I wonder if the hydrocarbons can change the pH in a way that would give those results...  definitely interesting!!!


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## sdadam (Jun 8, 2013)

Ummmm...

A low ETCO2 reading is expected for a metabolic acidosis patient.

The active ingredient in break fluid is ethylene glycol, when ingested it is metabolized by alcohol dehydrogenase in to (mainly) glycolic acid and oxalic acid.

This increase in acid production results in a decrease in bicarb, without bicarb protons are not converted to CO2 to breath off.

This patient is in anion-gap metabolic acidosis and the low ETCO2 is expected.


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## chaz90 (Jun 8, 2013)

sdadam said:


> Ummmm...
> 
> A low ETCO2 reading is expected for a metabolic acidosis patient.
> 
> ...



Not quite right. In metabolic acidosis, Le Chatelier's principle shows CO2 levels will increase to balance out the increased H+ ions. With an intact respiratory compensatory mechanism, they will hyperventilate to blow off excess CO2. See DKA for an example. This may lower the EtCO2 some from its elevated acidotic levels, so you'll see a balance between both.


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## Carlos Danger (Jun 8, 2013)

sdadam said:


> Ummmm...
> 
> A low ETCO2 reading is expected for a metabolic acidosis patient.
> 
> ...



You seem to be confusing pH with Etco2

More hydrogen ions (lower pH) = more Co2 in blood = more Co2 in expired gas (increased Etco2)


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## ghevener (Jun 9, 2013)

The common thread I hear from this is hyperventilation. But as brought up previously the low EtCO2 can very well be not a reliable indicator of the PaO2 (the amount of oxygen in serum plasma). As brought up previously by 46young and halothane for an appropriate correlation between EtCO2 and PaCO2 you have to have all the following factors being functioning normally: enough CO2 production and diffusion to circulation; enough cardiac output to get the CO2 from the cells to the lungs; the ability for CO2 to diffuse into the aveoli from the bloodstream; and enough minute volume to get the CO2 out of the airway. If there is a breakdown in any of the above 4 processes then the EtCO2 will not equal the PaCO2. The prime example of this that we are all taught is the low EtCO2 in a patient with a PE, but many of us seem to just focus on either PE or hyperventilation as the end all causes for a low EtCO2. 
Capnography has it's uses, and I think it's the biggest advancement in our practice of medicine in quite a while, but remember that it by itself has it's limitations. We can treat hypercapnia by EtCO2 only but we can not treat hypocapnea by EtCO2 alone. If you are assuring proper minute ventilations for your patient and the EtCO2 is still low than it is probably not an issue that ventilation changes are going to help. 
The only way to be able to see if the EtCO2 matches appropriately with the EtCO2 is to draw an ABG on the pt so you can measure the PaO2 directly. Without that even though your EtCO2 is low the actual PaO2 could be low, normal, or high. Remember that they drank a very caustic liquid that can cause many violent changes to the body, not to mention the risk of aspirating it. The end of the day be sure to ensure proper minute ventilations and treat your patient like always and never just the machine.


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## MySandie (Jun 29, 2013)

*IMO, that type of cannula should be used more often in hospitals*



RustyShackleford said:


> We use the same type as noted above and they have always been pretty accurate when compared to in hospital/ETT readings.



The picture of the cannula that redirects oral breaths back into the body is awesome.  I wish they were used in hospitals, because it would help with dx.


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## systemet (Jul 2, 2013)

There's a few take home points here:

* End-tidal CO2 is a product of cardiac output and PaCO2.  It doesn't always directly correlate to PaCO2, but generally the PaCO2 is not less than the PETCO2.  

* This patient likely has a partially compensated anion gap metabolic acidosis from the toxic alcohol.  With respiratory compensation the PaCO2 and ETCO2 will decrease.


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## linds (Jul 16, 2020)

Hi! EMT and Paramedic student here. 
I've had a EtCO2 of 9 and I was still completely coherent!
I get panic attacks semi-regularly and after experiencing one in school and having my professors hook me up to the monitor and teach me what was happening while I was deep in it - I was fascinated by my experiences. This didn't stop them however, and it sort of made them worst because I knew what was happening and I knew what would help, but my "lack of control" made me more afraid.

My experience was this: I was full-time paramedic student (and EMT) working at a haunted house (as an actor), I had a panic attack and went and sat with the medics. They put the pulse ox and nasal cannula l on and I watched my EtCO2 decline rapidly. I had only had this experience once, when my professors were instructing me. Since then I had many experiences with carpal pedal spasms and oh MAN they're weird. 
Basically, my sats were 94% and my end tidal read 9. The medics could not believe it because I was sitting up and obviously still awake. One thing that happens with my panic attacks is that I tend to hold my breath and breathe out fast and hard, not really fast and shallow. 
They didn't have O2 with them (lol), but I eventually got better on my own. I haven't met another medic who has experienced a panic attack, and I'm saddened by the number of medics who don't take these seriously. -glad to see this isn't happening in this thread-

tl;dr I had an ETCO2 of 9 and was upright and conscious.


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## jgmedic (Jul 17, 2020)

1. Holy Necropost
2. Of course your ETCO2 was low in a panic attack, you were hyperventilating, so your sats would stay high and ETCO2 would be down. This is not surprising at all., putting anxiety pts on o2 is useless in a hypervent situation. Breath coaching is by far the most effective tool in my experience.


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## Tigger (Jul 18, 2020)

linds said:


> Hi! EMT and Paramedic student here.
> I've had a EtCO2 of 9 and I was still completely coherent!
> I get panic attacks semi-regularly and after experiencing one in school and having my professors hook me up to the monitor and teach me what was happening while I was deep in it - I was fascinated by my experiences. This didn't stop them however, and it sort of made them worst because I knew what was happening and I knew what would help, but my "lack of control" made me more afraid.
> 
> ...


Why would you need oxygen with an SpO2 of 94 and what would oxygen do to help it?

Someone hyperventilating at a rate of 70 or 80 is going to have a low, possibly less than 10 EtCO2. Not sure what's unusual about that. I used to put EtCO2 cannulas on hyperventilating patients in an effort to have them watch themselves improve with breathing exercises, but that's a bit expensive for a refusal and of debatable utilities. 

It's a bit shameful how few EMS providers really learn to manage stress and anxiety, to include when and when not to use medication.


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## E tank (Jul 18, 2020)

Tigger said:


> Why would you need oxygen with an SpO2 of 94 and what would oxygen do to help it?
> 
> Someone hyperventilating at a rate of 70 or 80 is going to have a low, possibly less than 10 EtCO2. Not sure what's unusual about that. I used to put EtCO2 cannulas on hyperventilating patients in an effort to have them watch themselves improve with breathing exercises, but that's a bit expensive for a refusal and of debatable utilities.
> 
> It's a bit shameful how few EMS providers really learn to manage stress and anxiety, to include when and when not to use medication.


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## linds (Jul 18, 2020)

Tigger said:


> Why would you need oxygen with an SpO2 of 94 and what would oxygen do to help it?
> 
> Someone hyperventilating at a rate of 70 or 80 is going to have a low, possibly less than 10 EtCO2. Not sure what's unusual about that. I used to put EtCO2 cannulas on hyperventilating patients in an effort to have them watch themselves improve with breathing exercises, but that's a bit expensive for a refusal and of debatable utilities.
> 
> It's a bit shameful how few EMS providers really learn to manage stress and anxiety, to include when and when not to use medication.


They were freaking out a bit about their lack of supplies and one of the medics hadn't even seen a panic attack before. When I started getting the carpal pedal spasms I was trying to explain to him how they felt and think he was stressed because he couldn't do anything for me, even though I told him I just had to chill tf out. I've never needed O2 because yeah it's not going to do anything.


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## Tigger (Jul 19, 2020)

Ran an anxiety attack the other day, the driver/engineer asked if he should go retrieve a paper bag with zero irony.


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## Peak (Jul 19, 2020)

Had a patient with a PCO2 of 6, sitting up and conversational. Don’t underestimate the bodies ability to compensate until the point of collapse.


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## ffemt8978 (Jul 19, 2020)

Peak said:


> Had a patient with a PCO2 of 6, sitting up and conversational. Don’t underestimate the bodies ability to compensate until the point of collapse.


That ability to compensate is often the only thing that gives EMS a chance to save them.


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## johnrsemt (Jul 20, 2020)

In training when we got Capnography I was able to get my RR up to 80-90 with it and SP02 on and keep it there for about 15 minutes.  readings were 96-99%, and 25-30.  Drove the 2 medics teaching the class crazy, because "It shouldn't be happening".  Just like it shouldn't happen that I walk around with a room air of 88% and bp 80/40.   Some people and patients are strange and don't fit the 'normal ranges'


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## Peak (Jul 20, 2020)

johnrsemt said:


> In training when we got Capnography I was able to get my RR up to 80-90 with it and SP02 on and keep it there for about 15 minutes.  readings were 96-99%, and 25-30.  Drove the 2 medics teaching the class crazy, because "It shouldn't be happening".  Just like it shouldn't happen that I walk around with a room air of 88% and bp 80/40.   Some people and patients are strange and don't fit the 'normal ranges'



Have you put had an echo?


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## Carlos Danger (Jul 20, 2020)

Peak said:


> Have you put had an echo?


I was wondering the same thing.


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