Regarding: Time to initiation of extracorporeal membrane oxygenation in conventional cardiopulmonary resuscitation affects the patient survival prognosis

After a thorough analysis of the study by Ji-Hoon Sim et al., published in the Journal of Internal Medicine, we express our appreciation for their findings that the early initiation of extracorporeal membrane oxygenation (ECMO) during cardiopulmonary resuscitation (CPR) significantly improves short- and long-term survival outcomes. The study highlights the critical role of timely ECMO application in enhancing treatment results for patients receiving extracorporeal PCR (ECPR) [1]. Nevertheless, we believe there are several key issues within the study that could impact the interpretation of the results.

First, the exclusion criteria of the study did not specifically mention whether certain populations that could significantly affect the study conclusions were excluded. These include patients over the age of 75, those with end-stage malignancies, those requiring ongoing life support, patients with cardiac tamponade due to aortic dissection, and those with persistent intracranial hemorrhage or severe brain injury [2]. For instance, elderly patients may have different physiological characteristics and disease risks, which could affect their response to treatment and recovery capabilities compared to younger patients. The overall health status and life expectancy of patients with end-stage malignancies are already severely compromised. If these patients were not properly excluded, their inclusion could lower overall survival rates, thereby affecting the assessment of ECMO efficacy. Patients who required continuous life support prior to cardiac arrest may have a poorer baseline health status, which could influence the accuracy of the study's findings regarding the relationship between the timing of ECMO initiation and survival rates.

Second, although the study distinguished between out-of-hospital cardiac arrest (OHCA) and in-hospital cardiac arrest patients, it did not detail whether key pre-hospital characteristics of OHCA patients were recorded [2]. Such characteristics include the time of collapse, the presence of a witness, bystander CPR, the occurrence of transient return of spontaneous circulation before hospital arrival, initial shockable rhythm, and the interval from collapse to the initiation of CPR. Pre-hospital constraints may delay the start of ECMO, thereby prolonging the duration of low blood flow in patients, affecting organ perfusion and, ultimately, prognosis [3]. Moreover, the ECMO outcomes for OHCA patients may be affected by the quality of emergency medical services and pre-hospital treatment systems. The difficulty of manual CPR during ambulance transport suggests that mechanical CPR before the start of ECMO could yield different survival outcomes. The lack of these data could limit a comprehensive understanding of the pre-hospital situation and resuscitation process for OHCA patients, which is crucial for analysing the impact of the CPR-to-ECMO interval on prognosis.

Lastly, the study did not mention specific details of post-cardiac arrest care, such as transfusions, ventilator settings, and treatment of infectious complications. These care measures are typically vital components of the comprehensive treatment and management of post-cardiac arrest patients, significantly impacting their recovery and prognosis. Additionally, the study did not record important observational indicators after the start of ECMO care, such as early achievement of mean arterial pressure, therapeutic temperature management, left ventricular ejection fraction post-ECMO, successful weaning from extracorporeal life support, and complications during ECMO, including access site bleeding, limb ischemia, and intracranial hemorrhage. These factors have been proven to be important in affecting ECMO prognosis [4]. In summary, although the conclusions of Ji-Hoon Sim et al.’s study are enlightening, only after further analysis and addressing the aforementioned issues can the credibility and practicality of the study's conclusions be enhanced.

Wei-Zhen Tang: Conceptualization; methodology; validation. Zhe-Ming Kang: Conceptualization; validation; visualization; formal analysis. Tai-Hang Liu: Formal analysis; investigation.

The authors declare no conflicts of interest.