The relationship between no-flow interval and survival with favourable neurological outcome in out-of-hospital cardiac arrest: Implications for outcomes and ECPR eligibility

Background: The "no flow" interval is the time from out-of-hospital cardiac arrest (OHCA) to cardiopulmonary resuscitation (CPR). Its prognostic value is important to define for prehospital resuscitation decisions, post-resuscitation care and prognostication, and extracorporeal cardiopulmonary resuscitation (ECPR) candidacy assessment. Methods: We examined bystander-witnessed OHCAs without bystander CPR from two Resuscitation Outcomes Consortium datasets. We used modified Poisson regression to model the relationship between the no-flow interval (9-1-1 call to professional resuscitation) and favourable neurological outcome (Modified Rankin Score <= 3) at hospital discharge. Furthermore, we identified the no-flow interval beyond which no patients had a favourable outcome. We analysed a subgroup to simulate ECPR-treated patients (witnessed arrest, age < 65, non-asystole initial rhythm, and >30 min until return of circulation). Results: Of 43,593 cases, we included 7299; 616 (8.4%) had favourable neurological outcomes. Increasing no-flow interval was inversely associated with favourable neurological outcomes (adjusted relative risk 0.87, 95% CI 0.85-0.90); the adjusted probability of a favourable neurological outcome decreased by 13% (95% CI 10-15%) per minute. No patients (0/7299, 0%; 1-sided 97.5% CI 0-0.051%) had both a no-flow interval >20 min and a favourable neurological outcome. In the hypothetical ECPR group, 0/152 (0%; 1-sided 97.5% CI 0-2.4%) had both a no-flow interval >10 min and a favourable neurological outcome. Conclusions: The probability of a favourable neurological outcome in OHCA decreases by 13% for every additional minute of no-flow time until high-quality CPR, with the possibility of favourable outcomes up to 20 min.