Odd EtCO2

chaz90

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I ran a bit of an unusual cardiac arrest this AM and thought I'd run a couple questions by the forum. In short, we witnessed the arrest but have no history from the patient or anyone else. A third party caller from another town contacted 911 and advised the patient had contacted her and complained of "difficulty breathing." We arrived a short time later and found the patient seated, unresponsive, gasping, extremely hypoxic, and with clenched muscles and rightward gaze. She had palpable (but weak) radial pulses at a rate of ~45. Before we were able to perform further assessment or any intervention, she began to brady down into an agonal rhythm and lost carotid pulses.

In the course of working this code, we placed a capnography EtCO2 cannula on her during our ventilations with a BVM per our standard policy. We had excellent compliance and easy ventilations with effective chest rise and fall noted during a period of ROSC, but our capnography output was quite low at ~5 mm Hg. I didn't think much of it as NC EtCO2 readings during arrests are understandably a bit hit or miss. I was far more surprised after I intubated the patient and still only had an EtCO2 reading of 5 mm Hg during ventilations through the ETT. Tube placement was confirmed again with video laryngoscopy and the cuff was noted to be inflated. As the patient was jostled during some movement, the EtCO2 gradually increased (no rhythm change from asystole) and then remained at ~40 mm Hg. At this point, the EtCO2 baseline remained high. I've attached a picture to demonstrate what I mean here. I'm accustomed to being able to visualize LUCAS compressions on the EtCO2 waveform, but typically the waveform returns to zero between ventilations.

063560461658aa1d0087421bf04bb7c5.jpg


This picture shows three waveforms and displays lead II on top in black, SpO2 pleth in the middle in blue, and the EtCO2 waveform on the bottom in orange. The LP15 calibrated and zeroed itself with the EtCO2 numeric at the end of ventilation being ~50 mm Hg at this point. You can see the compressions on the EtCO2 waveform along with a slightly higher and prolonged wave during ventilations.

Our best guess was that the patient may have suffered from a PE causing the arrest and then possibly dislodged the clot during compressions and jostling causing the rise in EtCO2 values. I remain a bit confused as to why the baseline would not return to zero or why she seemed to continually be exhaling some CO2 (or at least reading that way on the monitor). We had a brief period of ROSC and mechanical capture with pacing in which compressions were discontinued and the EtCO2 readings looked the same, so we don't believe it was caused by the continuous compressions not allowing the lungs to fully exhale. I haven't seen anything quite like it before. Any other ideas or additional experience with anything similar?
 

STXmedic

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My first thought was PE of course. You mentioned after jostling it increased. Is it possible you mainstem'ed the tube initially, and the right lung was the side with inhibited circulation? Then the jostling displaced the tube back far enough to effectively ventilate both lungs? I can't imagine a clot large enough to cause arrest simply dislodging and immediately allowing for normal perfusion, though I suppose it's possible. The circulatory tree gets narrower before it widens out again... Though I guess it could have just been terribly bad luck on where it lodged.

As to the waveform not returning to baseline, I've got nothing. Did you try switching out the EtCO2? Apparently contamination/condensation can be a cause of increasing baseline.
 
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chaz90

chaz90

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We actually did switch out the in line EtCO2 adapter because we thought the same thing. I also trouble shot it afterwards with a new capnography set up and it worked perfectly, returning to a baseline of zero like normal. It exhibited the same characteristics using a BVM and our ventilator, so I don't believe it was a problem with stacking or exhalation port blockage on our vent circuit.

As far as tube position, I guess anything is possible. I visualized the cuff as going just past the vocal cords, and secured it with a tube holder at 23 cm at the lips. There didn't appear to be any notable change in position every time I checked it. I wouldn't imagine that would be enough to right main stem it, but I can't make any promises. Good thoughts!
 

STXmedic

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What about an actual airway obstruction? Like a mucous plug or FBAO that could've gotten pushed deeper?

Edit: Nevermind. You mentioned excellent compliance, so probably not.
 

Carlos Danger

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My first thought was that the ETT was in a bad position or kinked, but that doesn't seem likely if the bag squeezed fine and you were getting good chest excursion and recoil.

What are the differentials for a low very low ETc02?
  1. poor pulmonary blood flow (cardiac arrest, severe hypotension, massive PE, tension pneumothorax)
  2. poor mechanical ventilation (airway obstruction, low tidal volumes, ET tube kinked, equipment problem / tubing issue)
  3. poor gas exchange (severe pulmonary edema, severe atelectasis, etc)
  4. major metabolic issue (massive alkalosis, very severe hypothermia)
Of those, given your description I'd guess it was most likely something in category 2. And since you felt you were ventilating well, I'd say it must have been an equipment issue. Certainly not unheard of to have a problem with the tubing or the monitor.

Could have been a weird issue with the patient, though - as you know, the don't read the same textbooks we do, so they don't always do what we think they should :)
 

BassoonEMT

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A little late to this party, but in addition to the above ideas, when attaching the etco2, did you plug it in and allow for baseline reading before attaching to the tube? Or did you put it on the tube and then plug it in to the monitor?

They say it should be plugged in first, but i've seen it done both ways seemingly without issues. But who knows it could have something to do with it.
 

Bobbob1354

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Even more late to this party, could the patient have taken any antacids. They have the potential to cause abnormal capnography readings.
 

NomadicMedic

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A little late to this party, but in addition to the above ideas, when attaching the etco2, did you plug it in and allow for baseline reading before attaching to the tube? Or did you put it on the tube and then plug it in to the monitor?

They say it should be plugged in first, but i've seen it done both ways seemingly without issues. But who knows it could have something to do with it.

LifePak 15s auto calibrate. It's never been an issue in the past.
 

usalsfyre

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Tubes can sometimes sit "just" above the glottis and still ventilate and it will look similar to this, but you mention seeing it go through. So I got nothing.
 
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