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Extracorporeal cardiopulmonary resuscitation versus conventional CPR in cardiac arrest: be aware of the temporal selection bias

The Original Article was published on 21 February 2024

To the editor

We read with great interest the recent meta‑analysis and trial sequential analysis published in the Journal by Low et al. [1] reporting the benefit of extracorporeal cardiopulmonary resuscitation (ECPR) for both in-hospital cardiac arrest (IHCA) and out-of-hospital cardiac arrest (OHCA) outcomes improvement.

However, we believe that few issues deserve the results’ interpretation and manuscript’ conclusions.

First, the intrinsic OHCA and IHCA prognoses are clearly different [2]. While OHCA has been more studied than IHCA, their chain of survival are different and, OHCA outcome is better than IHCA [2]. Consequently, it is surprising to mix IHCA and OHCA in a meta-analysis. All the more since in Low et al. study [1], the IHCA prognosis was assessed in 4 studies out of 13, representing approximately 150 patients out of the 14,048 patients analyzed, i..e. nearly 1% of all patients.

In addition, the studies included in this meta‑analysis were mainly, but not exclusively, carried out after 2015, including the study by Kim et al. [3] representing approximately 50% of the patients. Before 2015, ECPR eligibility criteria were not the priority in the studies, which were mainly feasibility studies. Since 2015, the experts recommended the definition of criteria, i.e. eligibility criteria, in order to select patients with the best chance of success and to avoid futile ECPR implementation [2]. Among the eligibility criteria, a shockable rhythm is in itself associated with a better prognosis [4]. Thus, after 2015, ECPR studies concern selected patients, i.e. those with the highest expected success rate, that consequently directly impacts both studies’ design and studies’ results [5].

Beyond these limitations, we agree that ECPR should be considered in both IHCA and OHCA among “selected” patients, i.e. those whose prognosis is, a priori, favorable and who will benefit most from ECPR implementation.

Availability of data and materials

Not applicable.


  1. Low CJW, Ling RR, Ramanathan K, Chen Y, Rochwerg B, Kitamura T, Iwami T, Ong MEH, Okada Y. Extracorporeal cardiopulmonary resuscitation versus conventional CPR in cardiac arrest: an updated meta-analysis and trial sequential analysis. Crit Care. 2024;28(1):57.

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  2. Perkins GD, Graesner JT, Semeraro F, Olasveengen T, Soar J, Lott C, Van de Voorde P, Madar J, Zideman D, Mentzelopoulos S, Bossaert L, Greif R, Monsieurs K, Svavarsdóttir H, Nolan JP; European Resuscitation Council Guideline Collaborators. European Resuscitation Council Guidelines 2021: Executive summary. Resuscitation. 2021;161:1–60.

  3. Kim SJ, Han KS, Lee EJ, Lee SJ, Lee JS, Lee SW. Association between extracorporeal membrane oxygenation (ECMO) and mortality in the patients with cardiac arrest: a nation-wide population-based study with propensity score matched analysis. J Clin Med. 2020;9(11):3703.

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  4. Monsieurs KG, Nolan JP, Bossaert LL, Greif R, Maconochie IK, Nikolaou NI, Perkins GD, Soar J, Truhlář A, Wyllie J, Zideman DA, ERC Guidelines 2015 Writing Group; European Resuscitation Council Guidelines for Resuscitation 2015: Section 1. Executive summary. Resuscitation. 2015;95:1–80.

  5. Karve S, Lahood D, Diehl A, Burrell A, Tian DH, Southwood T, Forrest P, Dennis M. The impact of selection criteria and study design on reported survival outcomes in extracorporeal oxygenation cardiopulmonary resuscitation (ECPR): a systematic review and meta-analysis. Scand J Trauma Resusc Emerg Med. 2021;29(1):142.

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RJ, ACV and BV wrote and revised the manuscript.

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Correspondence to Romain Jouffroy.

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Jouffroy, R., Vie, AC. & Vivien, B. Extracorporeal cardiopulmonary resuscitation versus conventional CPR in cardiac arrest: be aware of the temporal selection bias. Crit Care 28, 126 (2024).

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