Case Four: PEA or Low Cardiac Output?

"A number of patients with the so-called pulseless electrical activity (PEA), actually have cardiac activity. More than eight of ten patients believed to be in PEA have synchronous cardiac wall motion, and over 40% have a measurable aortic pressure. (Bocka et al., 1988; Paridis et al., 1992; Cantineau et al., 1994). Capnography can help distinguish between PEA and very low cardiac output arrest states (Sanders et al., 1985; Isserles & Breen, 1991; Cummings & Hazinski, 2000.)"

- Capnography: Clinical Aspects; edited by J.S. Gravenstein, Chapter 8, Capnography in Transport, M.A. Frakes, Page 68;Cambridge University Press, 2004.

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2 cases to talk about:

Case #1 happened last February and at the time I didn't know too much about capnography, and so I didn't add it all up.

I had intubated a patient with agonal respirations, who had now stopped breathing on her own and who now had no palpaple pulse and I couldn't get a blood presure. She was intubated so I was ventilating her, but she was a DNR so I couldn't start compressions. The full story is described in my medic blog under the heading Scenario.(The story describes the dilemna because the patient was a DNR, but not a DNI).

Here's what she looked like on the monitor:

Under normal circumstances we would start CPR under the PEA algorithm. No palpaple pulse, no BP, not breathing on own, unresponsive. However, while being ventilated the patient had an ETCO2 of 14-20 without CPR. In other words, capnography revealed she still had cardiac activity that was producing some output, albeit very low. Still, it clearly reveals that the patient is not in PEA. If this patient were not a DNR, without capnography, you would have no choice but to begin CPR. With capnography, maybe it raises some question about how to proceed. Do you just do a dopamine drip or do you do CPR anyway?

Case #2 I had a slightly different call a few months earlier where the patient was not a DNR.

Here's the initial rythm:

Not too good.

Initial capnography on intubation was 7. The patient got four epis and two atropines. The end tidal went up to 11, and then 25 at which time the monitor showed a rate of 130.

Still, now en route to the hospital, we could not feel a pulse or hear a BP. She had no respiratory effort of her own. The dilemna was without capnography this patient was still in PEA. Since I was new to capnography and didn't quite understand it, as we rolled down the hall to the ER, I did psuedo CPR (compressions but not deep or hard enough to crunch a rib) because I did not want to lose my medical control for not doing compressions on someone in PEA, but at the same time I felt there had to be some cardiac output to have a capnography reading of now 30.

(I apologize for the poor strips -- I was not collecting them at the time and have had to scrounge around in boxes to find these.)

Again keep in mind I had no training on capnography (beyond being told I had to put it on every intubated patient to get a wave form to show I had the tube in the proper place), and was struggling to think it through. I had never thought of or encountered such a situation. Today, clearly I would have said: her capnography is 30. She's producing carbon dioxide. She has cardiac output. She is not in PEA. As it turned out, they got a BP of 125/70. They ceased CPR.

My question (at the risk of asking a stupid question) that I need to run by some physicians is this: Prehospitally, lacking a dopler, but possessing continuous capnography, assuming we can't feel a pulse or hear a blood pressure and the patient has no respiratory effort of their own, how high should the capnography be(assuming no active compressions) before you can safely withhold compressions? You would clearly do compressions at 3, and you would clearly not do compressions at 35. What about 14?

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UPDATE:

I encountered an excellent slide show on capnography by Dr. Strayer from McGill College. He includes the following slide:

Here are his comments:

"PetCO2 can differentiate between PEA and pseudo-PEA, which probably accounts for the majority of our PEA ROSCs, especially in cold water or overweight people, where pulse palpation carries a high false-negative rate. Ultrasound is probably a more useful modality in this application, however. In this graphic, the patient has no palpable pulses but a persistent PetCO2 of 20, without CPR (stopped at point A). CPR is restarted at point B, which doesn't do much. At point C, dopamine is infused. At point D, a pulse is palpated and cardiac compressions are halted."