Association between scene time interval and clinical outcomes according to key Utstein factors in out-of-hospital cardiac arrest

There is no consensus on the appropriate length of time spent on the scene by emergency medical services. Hence, our study aimed to investigate the association between the scene time interval (STI) and clinical outcomes of out-of-hospital cardiac arrest (OHCA) and determine whether this association is affected by key Utstein factors—witness status, bystander cardiopulmonary resuscitation, and initial electrocardiogram rhythm. This study is a cross-sectional study, using data between 2017 and 2020 from a nationwide, population-based, prospective registry of OHCA. The primary exposure is the STI, which was categorized into 3 groups: short (0 < STI ≤ 12 min), middle (13 ≤ STI ≤ 16 min), long (17 ≤ STI ≤ 30 min). The main outcome was good neurological recovery. Multivariable logistic regression and interaction analyses were performed to estimate the effect of STIs on study outcomes according to key Utstein factors. Witnessed, bystander cardiopulmonary resuscitation, and an initial shockable rhythm were associated with high survival to discharge and good neurological recovery, whereas prolonged STI was associated with low survival to discharge and poor neurological recovery. In patients with witnessed arrest, increased STI caused a more rapid decrease in survival to discharge than in non-witnessed cases (witnessed arrest: 0.56 (0.51–0.62) in middle STI and 0.33 (0.30–0.37) in long STI, non-witnessed arrest: 0.72 (0.61–0.85) in middle STI and 0.53 (0.45–0.62) in long STI. In patients with an initial shockable rhythm, increased STI caused a more rapid decrease in survival to discharge and neurological recovery than in initial non-shockable cases. Longer STIs were associated with poorer OHCA outcomes, and this trend was further emphasized in patients with witnessed OHCA and OHCA with an initial shockable rhythm.