Waveform Capnography Part 3

Wow, it’s been a LOOOOOOONG time since I visited this category. Sorry for taking so long with Part 3, if you need to knock the cobwebs out of what I’ve written on this topic in the past here is Part 1 and Part 2.

Ok, so what did I promise you the last time? Oh yes, patterns in different respiratory issues.

So the last time we talked about this we played with the normal pattern for a ETCO2 waveform, which is the equivalent of a plateau with fairly sharp delineations between phases and the normal values of exhaled CO2 being between 35-47 mmHg. So now that we’ve established what “normal” is, let’s look at some things that aren’t normal.

Abnormally High Numbers and Funny Looking Waves

“Hey RJ, the numbers were like 50 mmHg and up the last time I used capnography!’

High numbers indicate CO2 retention (bonus question: which is common found in what respiratory condition?) which means that the patient isn’t moving any CO2. You can fix this with mechanical means such as a BVM or CPAP (if the assessment indicates obstructive
pulmonary disorders) or if the respiratory depth is adequate, you can try using a non-rebreather mask.

I will tell a story. When I was a medic student riding at Xenia Township in Ohio, we responded to a report of an unconscious female out in the sticks. On arrival, we found a 60-some odd female lying on her couch. She was obtunded, with questionable pupil size, normal blood glucose, depressed respiratory drive, sinus rhythm, normal 12 lead ECG, and a slightly elevated blood pressure. We expedited her transport, and we couldn’t wake her up despite the use of naloxone (we suspected she had overdosed on recently prescribed pain medication) and a questionable CVA screen. Turns out, it was none of the above. Had we placed a capnography probe we would have found her PETCO2 to be in the 60-80 mmHg range and could have corrected her mental status change using mechanical ventilation.

Why tell you this? Because the technology was brand new to EMS then (it was a new feature on our recently upgraded LifePak 12’s) and if we had dug a little deeper we would have found COPD in her history, specifically chronic bronchitis. We could in-lined a breathing treatment through the BVM and created positive pressure in her alveoli and open them up, creating the release of trapped air and bringing her back to normal level. The next time we encountered her with the same issue (which was about 3 months later) I knew exactly how to correct her problem. 80% of all diagnosis is history related (and we do diagnose, don’t get me started) so make sure your history is as complete as the situation allows.

In bronchospasm (which is a form of pulmonary obstruction), the waveform, when analyzed closely, may look like something of a shark fin. Why is that?

Well, the Expiration phase (which is the Phase I and II waves) is prolonged due to obstruction. This makes the wave kind of smooth out a bit as the patient attempts to force air through the obstruction. This patient may exhibit the classic respiratory distress signs such as tripoding, nasing flaring, etc, and will appear in trouble before you even put the probe on. As you remember, those breathing patterned are typical when the patient is attempting to increase the PEEP (positive end expiratory pressure) in response to air trapping.

I’ve also seen the numbers high in a post arrest in the presence of DKA, the science indicates that PETCO2 is an accurate measurement even for regular patients in DKA for PCO2, which can help you determine if DKA is present.

This is kind of a quick end to a long standing series but I wanted to put out an ending like I had promised so long ago.