Delta end-tidal CO2 in PEA: Does the difference matter?

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Mohamed Hagahmed, MD, EMT-P
Mohamed Hagahmed, MD, EMT-P
Mohamed is an Emergency Medicine Physician and EMS director. His main areas of interest are Critical Care, Ultrasound, Prehospital Resuscitation, and Medical Education. Find him on Twitter @HagahmedMD

The Pre-brief

Cardiac arrest patients who are found to have an initial rhythm of pulseless electrical activity (PEA) have high mortality and a lower likelihood of survival. Physicians and EMS clinicians rely on the EKG and end-tidal CO2 (EtCO2) during the intra-arrest period of resuscitation in order to assess the resuscitation efforts and determine the likelihood of return of spontaneous circulation (ROSC). What is the role of delta EtCO2 in cardiac arrest patients with PEA?

PEA and Pseudo-PEA

In patients who are in true PEA, there are organized electrical impulses that do not translate into perfusing cardiac contractions. Pseudo-PEA, on the other hand, is characterized by electrical impulses with associated contractions of cardiac myocytes, but the forward flow of blood is not strong enough to generate a palpable pulse. Pseudo-PEA can be considered as a form of profound shock. This entity has a higher rate of ROSC and survival than true PEA.

To learn more about Pseudo-PEA, check it this great post by Dr. Peppin on CriticalCareNow.com.

Delta EtCO2 in PEA

This Canadian study looked exclusively at the association between the change in ETCO2 during resuscitation and ROSC in a cohort of cardiac arrest patients who were found to be in nontraumatic PEA. They designed a retrospective study that looked at prospectively collected data between January 2018 until December 2019 and included a total of 208 cardiac arrest patients who were treated by Paramedics in two large regions in Ontario, Canada. 

Delta ETCO2 was defined as initial ETCO2 recorded one minute after placement of an advanced airway by the Paramedic, and final ETCO2 value was documented one minute before ROSC or at the termination of resuscitation. The ROSC rate included in the analysis was 32%.

The authors found a positive linear relationship between delta ETCO2 and subsequent prehospital ROSC with an odd ratio (OR) of 1.74 (95% confidence interval [CI] 1.35 to 2.24; P value< 0.01) for every 10 mmHg increase in delta ETCO2. A delta ETCO2 of >20 mmHg had a specificity of 95% for predicting future ROSC events (95% CI 0.90 to 0.98).

Limitations and translation into practice

The primary limitations of this study are its retrospective design and lack of survival data, including neurologic recovery and survival to hospital discharge. The patients were treated primarily by a Paramedic crew in a very advanced and well-organized prehospital system which can limit its application in other settings that lack a full paramedic crew or ALS teams. It is also important to note the high ROSC rate in this cohort.

When caring for patients in PEA, taking into account the change in ETCO2 instead of relying on a single value during the arrest period can provide a better prognostication tool when caring for these patients. Clinicians should make extra efforts to ensure the delivery of high-quality chest compressions while promptly identifying and treating possible reversible causes of PEA.

The Debrief

  • Delta ETCO2 is a valuable tool in determining the prognosis of cardiac arrest patients in PEA.
  • A rising ETCO2 is associated with a higher chance of achieving ROSC.
  • When delta ETCO2 is >20, CPR should be continued.
  • Look for reversible causes when treating patients who are found in PEA.

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