**3.1 History and current use of extracorporeal cardiopulmonary resuscitation (ECPR) in pediatrics**

Extracorporeal membrane oxygenation (ECMO) use for cardiopulmonary resuscitation (CPR) in children was first described in the literature by del Nido in 1992 [41]. Since then, utilization of extracorporeal cardiopulmonary resuscitation has expanded in all pediatric age groups. The current definition of ECPR according to the Extracorporeal Life Support Organization (ELSO) is "the application of rapid-deployment venoarterial ECMO, to provide circulatory support in patients in whom conventional CPR is unsuccessful in achieving sustained return of spontaneous circulation (ROSC). Sustained ROSC is deemed to have occurred when chest compressions are not required for 20 consecutive minutes and signs of circulation persist" [42]. This definition has been used since ELSO updated its data definitions in 2018. Pre-2018, the ELSO definition of ECPR was "ECMO used for initial resuscitation from cardiac arrest" and did not include patients who had achieved ROSC when they were being cannulated for ECMO [43]. Apart from the ELSO definitions, the definition of ECPR varies in clinical studies, and this presents challenges with medical communication and synthesis of research.

Based on ELSO registry data, there has been an increasing use of ECPR in pediatric patients over the years [44]. The overwhelming majority of pediatric ECPR use reported in the literature is for in-hospital cardiac arrest (IHCA) [44]. There are only few reports of ECPR deployed in pediatric patients for out-ofhospital cardiac arrest (OHCA); 2% of pediatric ECPR cases reported to ELSO were for OHCA according to the 2016 pediatric ELSO registry report [44, 45]. There is one case report of out-of-hospital ECMO deployment in a child ("pre-hospital ECPR") [46].

From reported literature, the incidence of ECPR use varies from 5 to 27% of all pediatric IHCA cases between 2000 and 2016 [37, 47–49]. Of pediatric IHCA cases reported to the American Heart Association (AHA) Get With the Guidelines®- Resuscitation registry between the years 2000 and 2008, the incidence of ECPR use was 5–7% overall and 19–21% in patients with a cardiac diagnosis [37, 47]. More recently, the incidence of ECPR use was 27.2% in cardiac arrest patients reported to the Pediatric Cardiac Critical Care Consortium (PC4) registry between 2014 and 2016 [49].

The AHA had not included ECPR in Pediatric Advanced Life Support (PALS) guidelines until 2005 when guidelines were updated to include a consideration of ECPR in patients with a reversible cause of arrest or whose underlying condition could be treated by heart transplantation and who were located at an institution that could rapidly deploy ECMO, where effective conventional CPR had been started promptly [50]. Subsequent PALS updates have included this cautious recommendation to consider ECPR, particularly for cardiac patients with IHCA [18, 24, 51].
