BBB disruption following OHCA causes poor neurological prognosis and the changes in the prognostic value of biomarkers. However, several tools to evaluate BBB disruption are either invasive or cannot provide a continuous monitoring. Blood retina barrier (BRB) is similar with BBB anatomically and functionally, and BRB disruption influences the pupillary light reflex (PLR). Therefore, we studied on the correlation between BBB permeability and NPi in OHCA patients treated with TTM.This study was prospectively conducted between October 2020 and March 2022 (**** IRB 2019-07-033-09). NPi and Albumin quotientt (Qa) to determine BBB permeability were presented every 2 h until 24 h, and then 48 h and 72 h after ROSC. 25 patients were required after sample size calculation, and partial correlation analysis between NPi and Qa was performed with prognostic control. Changes in NPi and Qa over time were analysed using the generalised estimating equation. Basal characteristics were in table 1 and figure 1. Since this study aimed to elucidate the correlation between NPi and Qa, data on NPi and Qa during seizures were included in this study. Additionally, the drug used in this study was found to have no effect on NPi in previous studies. NPi was lower, and Qa was higher in the group with poor neurological prognosis (Table 2,3, and Fig. 2). There was a moderate negative correlation between NPi and Qa (Fig. 3).This study demonstrated that NPi had a moderate negative correlation with BBB permeability in OHCA patients treated with TTM. Therefore, further studies on prognostic strategies using biomarkers and NPi considering the increase in BBB permeability are needed. 1