Spring, it's time to ROSC.

Out-hospital cardiac arrest (OHCA) is a multi-factor disease. Many studies have correlated OHCA with a patient's lifestyle; unfortunately, less evidence highlights the correlation with meteorological factors. Methods: Analysis of 23959 OHCA rescue performed by the emergency medical system (EMS) of Lombardy Region, the most Italian populated region, in 2018 and 2019, the pre-pandemic era through a retrospective observational cohort study. The aim of the study consists on evaluating the probability of Return Of Spontaneous Circulation (ROSC) during months to highlight potential seasonal impact in ROSC achievement. In March and April, we highlight an increase of ROSC (OR: 1.20 95% CI 1.04-1.31; p < 0.001) compared to other months. During March and April, we highlight an increase of public access defibrillation (PAD) (3.5% vs 2.5%; p < 0.001), and a reduction of overage time of first vehicle on scene (11.5 vs 11.8; p < 0.001) and age of patient (73.5 vs 74.2; p < 0.01). Finally, we highlight a slight reduction of cancer patient (1.6% vs 1.1%; p = 0.01). We didn't register significant differences in the other variables analyzed as: onset place, sex, rescue team and the patient's death before the rescue arrive. We highlight a difference in ROSC probability during the first month of spring. We register few differences in patient characteristics and EMS rescue, though just PAD use and age clinically impact OHCA patients. In this study, we are unable to fully understand the modification of the probability of ROSC in these months. Even though four variables have a statistically significant difference, they can't fully explain this modification. Different variables like meteorological and seasonal factor must be considered. We propose more research on this item.