摘要BACKGROUND:Prolonged on-scene Advanced Life Support(ALS)in out-of-hospital cardiac arrest(OHCA)patients may enhance return of spontaneous circulation(ROSC),but the optimal duration of cardiopulmonary resuscitation(CPR)without initial prehospital ROSC remains unclear.We investigated the association between on-scene CPR duration and outcomes using nationwide data.METHODS:This prospective,multi-regional study(2015-2022)included medical cause OHCA patients who underwent Smart ALS(SALS).Data from emergency medical services(EMS)records,SALS logs,and hospital outcomes were analyzed.Logistic regression models were developed for prehospital ROSC,survival to discharge,and good neurological outcome(Cerebral Performance Category[CPC]1-2).RESULTS:Among 98,569 patients,34,989 were SALS-eligible and 16,052 received SALS.Predictors of ROSC included younger age,male sex,public arrest,witnessed arrest,bystander CPR,shockable rhythm,and shorter response/scene times.Longer on-scene CPR reduced probabilities of ROSC,survival,and neurological recovery at hospital discharge.Model AUROCs were 0.697(95%CI 0.676-0.717)for ROSC,0.836(95%CI 0.810-0.861)for survival,and 0.925(95%CI 0.904-0.946)for neurological outcome.CONCLUSION:On-scene CPR duration is a critical prognostic factor in OHCA.The proposed models highlight on-scene predictors that may inform decisions about CPR continuation and support individualized resuscitation strategies.External validation in other EMS systems is warranted.