Capnography and Intubation

When I was at a conference this past year one of the speakers said the data on prehospital intubation is so bad that if EMS had to go before the FDA to get approval to allow medics to intubate, it would be denied. Based on those studies, which include the LA pediatric intubation study, as well as many RSI studies, I can understand why.

However, those studies (to my knowledge) did not incorporporate continuous wave form capnography.

I believe continuous wave form capnography will eliminate all unrecognized misplaced tubes.

Capnography will prevent hyperventilation in head injured patients and critically injured patients(which may be the reason the RSI studies have poor results -- by letting medics intubate patients, RSI puts them at increased risk for hyperventiulation which is much easier to do with an patent airway and an ambu bag just begging to be squeezed.

And capnography can aid in the placement of difficult intubations. It can help prevent multiple attempts and even momentarily delayed recognition of misplaced tubes -- all of which cost the patient critical time without effective oxygenation and ventilation.

I believe continuous wave-form capnography will be the savior of prehospital intubation.


When many of us were taught to intubate the golden rule was:


The only ways we had to verify our tubes back then were this mantra, listening to lungs sounds and absence of belly sounds, looking for chest rise and mist in the tube -- all methods that cannot be considered fully reliable. My safety net was a partner who always held crick pressure for me and could tell me if I was in when he felt the tube pass under his fingers. That was my most reliable confirmation, but we didn't work together every shift so it was only part-time reliability. We didn’t have the bulb syringe then or colorimetric capnography much less continuous wave-form capnography.

While we all tried to live the mantra of never passing the tube unless we saw it pass through the chords, not all our tubes were in. Hopefully we recognized them right away – either by not hearing lung sounds or having warm gastric contents come flying up the tube to tell us we weren’t where we were supposed to be. How many times did we legitimately think we had passed the tube through the chords and how many times had we hoped we were through? Does the phrase “I think I’m in” sound familiar? particuarly coming from precepting or student medics?

As was proven in a recent study (see below), capnography has the ability to reduce misplaced ET tubes to zero if used. Instead of answering “You think! Pull it out!" or "You’re better hope you’re in – My license and mortgage and food in my babies mouths are riding on it!" Now capnography will tell you. He thinks right or he thinks wrong.

What I am going to suggest now is controversial. It stems from an interesting discussion I had with an articulate commenter on the November log. I suggest that with capnography’s ability to so quickly confirm or disprove a tube that it might no longer be a sin to pass the tube if you are not sure – particularly in the context of the difficult airway. If it wasn’t difficult we would easily see the chords, right? Now I’ll admit to shoving a tube or two in in my time. When you’re looking down the bloody throat of a gunshot or highway crash victim and you can’t tell what you are looking at or when puke and vomit are rising like a biblical Mississippi flood, sometimes you just put it where you think you see air bubbles or where anatomy wise the chords should be. When your own body is crooked trying to get an airway into the man wedged behind the toilet, sometime the view isn't the best. Ever tried an ice pick style tube?

In people whose chords are hard to see and who are difficult to bag, maybe the best thing to do is just shove the tube in to the best of your ability. And now with capnography, you’ll know you’re in or out almost instantly. Blind tubes are not after all that unusual in EMS. I have done digital intubations, intubations with a bougie and nasal intubations. All blind. I did them that way because that was the only way to get the tube. (Sometimes with IVs on people in extremis, you take a blind shot based on anatomy.) I say if you only have a partial view of the chords or the chords get obscured when you try to pass the tube, go for it if you think you can get it – as long as you have capnography to immediately check the tube.


Now here’s a tip. I haven’t done it yet in the field (it only occured to me the other day), but I think I will try it the next time I have to intubate a breathing patient. I have tested the concept and believe it will work.

Before you intubate, attach the capnography filter to the end of the ET tube, insert the stylet – it will fit as long as it is the thin kind, hook up the capnography to the machine, turn it on, and then go in for the tube. If your partner knows how to read wave forms he should be able to tell you if you are in or not when you ask. Either that or listen to the apnea alarm or the lack of an alarm. Make certain you have at least four good wave forms, and then pull the stylet and proceed with your routine checks.

For apneic patients you just have to have your partner ready to attach the ambu bag when you ask. No more looking around for the capnography filter -- it is already in place. Keep in mind as always for pulseless patients you may need a little CPR to get your wave form reading. And of course, you'll need to pull the stylet before you bag the patient.

Make certain you have an extra capnography filter available as backup because if by chance you miss your tube abd gastric contents come up, they will contaminate your filter in addition to your tube.

This method of attaching the capnography filter to the ET tube before intubating also works for nasal tubes. Watch the wave forms as you advance the tube while listening for respirations Once you think you are deep enough and then cough gag and you push through, verify with the wave forms. Just make certain you are not still in the hypopharanx.


Don't misunderstand me. I still believe you should strive for the gold standard of watching the tube pass through the chords. Don’t make capnography your crutch, but in a difficult airway, it may be your new best friend.


Postscript: The next morning my first call ended up being an intubation in which I used capnography to help intubate.

The call was for unresponsive patient with severe dsypnea. We found an 80 year old female with a GSC of 4-5 breathing at a rate of 60 with cool extremities. Unable to hear BP. Heart rate on the monitor 130-140. Blood sugar - 213. I attached the capnography filter to the end of the ET tube. Some of our ET tubes come with stylets already in them. I removed the stylet, but could not put it back in because it was to thick, so I used a thinner stylet. I went in, and had a hard time getting the woman's jaw open enough to see the chords. We don't have RSI so there was what we call inadequate relaxation. I could just barely see the chords under the epiglottis, but couldn't get the tube to pass through. Instead of checking by assessing breath sounds, I just looked at the monitor. The ETCO2 would just go straight and I'd know I had gone below the chords. I ended up nasally intubating her, which I probably should have done first, but I like to get a bigger tube in. The nasal tube went in great. I used a 6.0 and watched the wave forms as I fed it. The form went down to nothing, I pulled back and repositioned her head and then advanced the tube again, and felt it go through and had the big wave forms to confirm it.

Her SAT went up to 98% from the 80% and her ETCO2 came up from the mid twenties to low to mid thirties. She opened her eyes by the time we were in the ED.

(The next time I do a nasal tube I am just going to hit print button on the monitor from the start so I have a long strip to cut up and show the wave form changes.)

I'm still waiting to hear what was wrong with her - most likely sepsis.


Misplaced Tubes

The effectiveness of out-of-hospital use of continuous end-tidal carbon dioxide monitoring on the rate of unrecognized misplaced intubation within a regional emergency medical services system.

Silvestri S, Ralls GA, Krauss B, Thundiyil J, Rothrock SG, Senn A, Carter E, Falk J. Annals of Emergency Medicine, May 2005, pgs 497-503l

If there ever was an argument for requiring continuous ETCO2 monitoring on all intubations, this is it. Over a ten month period, in 11 counties in Florida there were 153 intubations. 93 (61%) used continuous ETCO2 Monitoring. 60 (39%) did not. Upon arrival at the Emergency department there were 14 (9%) unrecognized misplaced intubations. There were 0 (0%) misplaced tubes in the group that used continuous ETCO2 monitoring. There were 14 (23%) in unmonitored group.

The authors wrote: “The unobserved unrecognized misplaced intubation risk difference is compelling. This study demonstrates that it is possible to attain a zero unrecognized misplaced intubation rate.”

Four years earlier, another study was done in Florida that showed during an 8 month period out of 108 “intubated” patients brought to a large Florida ED, there were 27 misplaced tubes (27%) on arrival at ED. 18 were in the esophagus, 9 in hypopharanx. 17 of 18 esophageal intubations had an absence of expired CO2, the one with CO2 was nasally intubated and breathing their own. 4 of 9 hyphopharengal intubations had an absence of expired CO2. - Katz SH, Falk JL, Misplaced endotracheal tubes by paramedics in an urban emergency medical services system, Annals of Emergency Medicine, January 2001

The authors wrote: “The incidence of out-of-hospital, unrecognized, misplaced endotracheal tubes in our community is excessively high and may be reflective of the incidence occuring in other communities...Functionally, whether the tubes were misplaced initially or dislodged en route to the hospital makes little difference to the patient....Despite written protocols requiring the out-of-hospital use of ETCO2 devices in our community, we...found their use to be sporadic... We believe that routine use of this technique, both at the time of intubation and as an ongoing monitor during transport, could potentially eliminate the problem of unrecognized misplaced ETT placement....”

Bottom Line: Intubated patients should all have continuous ETCO2 monitoring.


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