Aims In refractory out-of-hospital cardiac arrest (OHCA) with prolonged whole-body ischaemia, global tissue injury proceeds even after establishment of circulation with extracorporeal cardiopulmonary resuscitation (ECPR). We aimed to investigate the role of biomarkers reflecting hypoperfusion, inflammation, and organ injury in prognostication of patients with refractory OHCA managed with ECPR. Methods and results This nationwide retrospective study included 226 adults with refractory OHCA managed with ECPR in Denmark (2011-2020). Biomarkers the first days after ECPR-initiation were assessed. Odds ratio of favourable neurological status (Cerebral Performance Category 1-2) at hospital discharge was estimated by logistic regression analyses. Cut-off values were calculated using the Youden's index. Fifty-six patients (25%) survived to hospital discharge, 51 (91%) with a favourable neurological status. Factors independently associated with favourable neurological status were low flow time = 12.8 x 10(9)/L, admission lactate