Regional cerebral oxygen saturation (rSO₂) offers a non-invasive indicator of brain perfusion. Despite its potential, the dynamics of rSO₂ during pre-hospital management of out-of-hospital cardiac arrest (OHCA) patients remain poorly understood. This study explored whether different temporal patterns of rSO₂ were linked to clinical outcomes. Between June 2013 and December 2019 in Osaka City, Japan, emergency life-saving technicians (ELTs) used portable devices to measure rSO₂ in OHCA patients. Serial changes were classified as type 1 (progressively increasing) or type 2 (stable or decreasing). Cases where monitoring began after return of spontaneous circulation (ROSC) were excluded. Outcomes included prehospital ROSC, survival to hospital admission, 1-month survival, and favorable neurological status (Cerebral Performance Category [CPC] 1–2). Among 87 patients analyzed, 40 exhibited type 1 patterns (median age 80.5 years, 50% male) and 47 type 2 patterns (median age 81 years, 59.6% male). After adjusting for potential confounders, type 1 patients were significantly more likely to achieve prehospital ROSC (27.5% vs. 4.3%; adjusted odds ratio [AOR] 5.67, 95% CI 1.04–30.96, p = 0.045) and survive to hospital admission (42.5% vs. 12.8%; AOR 3.56, 95% CI 1.11–11.43, p = 0.033). No statistically significant differences were observed in 1-month survival or neurological outcomes. An increasing trend in rSO₂ during pre-hospital resuscitation correlates with higher rates of ROSC and survival to admission. Real-time cerebral oxygen monitoring in the field may help optimize resuscitation approaches.
