Extracorporeal cardiopulmonary resuscitation for out-of-hospital cardiac arrest and in-hospital cardiac arrest with return of spontaneous circulation: be careful when comparing apples to oranges

Hwa Jin Cho; In Seok Jeong; Jan Bělohlávek

doi:10.4266/acc.2023.00731

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Editorial CPR/Resuscitation Extracorporeal cardiopulmonary resuscitation for out-of-hospital cardiac arrest and in-hospital cardiac arrest with return of spontaneous circulation: be careful when comparing apples to oranges: Hwa Jin Cho^1,2, In Seok Jeong^2,3, Jan Bělohlávek⁴; Acute and Critical Care 2023;38(2):242-243.
DOI: https://doi.org/10.4266/acc.2023.00731
Published online: May 31, 2023

¹Division of Pediatric Cardiology and Cardiac Intensive Care, Department of Pediatrics, Chonnam National University Children’s Hospital and Chonnam National University Medical School, Gwangju, Korea

²Extracorporeal Circulation Research Team, Chonnam National University Hospital, Gwangju, Korea

³Department of Thoracic and Cardiovascular Surgery, Chonnam National University Hospital and Chonnam National University Medical School, Gwangju, Korea

⁴²nd Department of Medicine-Department of Cardiovascular Medicine, First Faculty of Medicine and Charles University and General University Hospital, Prague, Liberec, Czech Republic

Corresponding author: Hwa Jin Cho Division of Pediatric Cardiology and Cardiac Intensive Care, Department of Pediatrics, Chonnam National University Children’s Hospital and Chonnam National University Medical School, 42 Jebong-ro, Dong-gu, Gwangju 61469, Korea Tel: +82-62-220-6646 Fax: +82-62-222-6103 Email: chhj98@gmail.com

• Received: May 23, 2023 • Accepted: May 24, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Extracorporeal membrane oxygenation (ECMO) is a resource-intensive and costly form of life support that is increasingly being applied to complex patients with cardiac arrest, now referred to as extracorporeal cardiopulmonary resuscitation (ECPR) [1]. The decision to use ECPR in patients with cardiac arrest is still made on a case-by-case basis, but initiation criteria vary among clinicians, institutions, and regions. Neurological outcomes after ECPR are among the most important outcomes, and a tool that is simple, quick, and utilizes readily available clinical information to predict the likelihood of various neurological outcomes could be extremely beneficial in the care of potential ECPR candidates [2]. However, current tools for predicting neurologic outcomes lack sufficient evidence for use in individual patients and need to be validated in patients with cardiac arrest [3-6].

In this issue of Acute and Critical Care, Lee et al. [7] investigated the ability of the respiratory quotient (RQ) measured within the first 24 hours after ECPR to predict neurological outcomes. The study included a relatively large and mixed population of in-hospital and out-of-hospital cardiac arrest (IHCA and OHCA) ECPR cases (a total of 155 participants) from a tertiary referral hospital in South Korea, spanning a period of 17 years. The research incorporated clinical variables collected within 24 hours following ECPR. Although the RQ was higher than the normal value in ECPR patients, it was not found to be associated with poor neurological outcomes.

The primary strengths of this study include its relatively large cohort of ECPR patients, the simplicity and ease of collecting variables, the inclusion of any patient on ECPR regardless of indication, and the more detailed data on RQ, which has been studied in many other fields, but not in this context. The significant risk factors associated with poor neurological outcomes in this study were age, CPR to pump-on time, and serum lactate levels above 7.1 mmol/L. Interestingly, initial lactate levels were lower than those reported in the largest randomized population to date, which may reflect the high percentage of patients who achieved return of spontaneous circulation before ECMO cannulation [3]. The authors hypothesized that patients with ECPR and poor neurological outcomes would tend to be older, have longer CPR to pump-on times, have a higher proportion of OHCAs, have more comorbidities such as hypertension and coronary artery disease, and have higher initial Sequential Organ Failure Assessment (SOFA) scores. However, this may not be true for different types of ECPR populations, particularly when comparing OHCA and IHCA cases. Among hypoxia parameters (e.g., RQ, venous-arterial difference in CO₂ tension, and serum lactate), lactate had the highest predictive power, which may warrant further discussion. The authors correctly emphasized that RQ was inferior to lactate in predicting poor neurological outcomes in patients who received ECPR in this study. They explained this finding by noting that blood gas measurements may be influenced by sweep gas and ECMO flow rates. The study incorporated data gathered over an extended period and did not include a group of patients who received support without ECMO, which may limit the study's power. Additional limitations encompass selection bias, the retrospective observational study design, and the exclusion of other centers from the study. A notably high percentage of patients (approximately 60%) experienced poor neurological outcomes, corroborating the earlier observation that this population does not constitute a true ECPR cohort, defined as those receiving implantation during ongoing chest compressions. As a result, the findings of this study may not be directly applicable to all ECPR patients.

The study by Lee et al. [7] identified several risk factors associated with poor neurological outcomes in patients undergoing ECPR, regardless of the underlying disease. Although the authors investigated a relatively novel variable (RQ) in ECPR patients, it was found to be less predictive than serum lactate levels. Nevertheless, the authors should be commended for providing a valuable stepping stone for predicting neurological outcomes, as their work helps to objectively quantify the risks and benefits of initiating ECMO versus continuing conventional care for individual patients.

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CONFLICT OF INTEREST

No potential conflict of interest relevant to this article was reported.

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AUTHOR CONTRIBUTIONS

Conceptualization: all authors. Writing–original draft: HJC. Writing–review & editing: all authors.

Acknowledgments

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References

1. Extracorporeal Life Support Organization (ELSO). ECLS international summary of statistics [Internet]. ELSO; 2022 [cited 2023 Apr 1]. Available from: https://www.elso.org/registry/internationalsummaryandreports/internationalsummary.aspx.
2. Neumar RW, Shuster M, Callaway CW, Gent LM, Atkins DL, Bhanji F, et al. Part 1: executive summary. 2015 American Heart Association Guidelines Update for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation 2015;132(18 Suppl 2):S315-67.PubMed
3. Belohlavek J, Smalcova J, Rob D, Franek O, Smid O, Pokorna M, et al. Effect of intra-arrest transport, extracorporeal cardiopulmonary resuscitation, and immediate invasive assessment and treatment on functional neurologic outcome in refractory out-of-hospital cardiac arrest: a randomized clinical trial. JAMA 2022;327:737-47.PubMed PMC
4. Bertic M, Worme M, Foroutan F, Rao V, Ross H, Billia F, et al. Predictors of survival and favorable neurologic outcome in patients treated with eCPR: a systematic review and meta-analysis. J Cardiovasc Transl Res 2022;15:279-90.Article PubMed PDF
5. Bertic M, Worme M, Foroutan F, Rao V, Ross H, Billia F, et al. Predictors of survival and favorable neurologic outcome in patients treated with eCPR: a systematic review and meta-analysis. J Cardiovasc Transl Res 2022;15:279-90.Article PubMed PDF
6. Kliegel A, Losert H, Sterz F, Holzer M, Zeiner A, Havel C, et al. Serial lactate determinations for prediction of outcome after cardiac arrest. Medicine (Baltimore) 2004;83:274-9.Article PubMed
7. Lee YI, Ko RE, Na SJ, Ryu JA, Cho YH, Yang JH, et al. Prognostic significance of respiratory quotient in patients undergoing extracorporeal cardiopulmonary resuscitation in Korea. Acute Crit Care 2023;38:190-9.Article

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Extracorporeal cardiopulmonary resuscitation for out-of-hospital cardiac arrest and in-hospital cardiac arrest with return of spontaneous circulation: be careful when comparing apples to oranges

Acute Crit Care. 2023;38(2):242-243. Published online May 31, 2023

DOI: https://doi.org/10.4266/acc.2023.00731

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