Association between blood urea nitrogen to creatinine ratio and neurologically favourable outcomes in out-of-hospital cardiac arrest in adults: A multicentre cohort study.

BACKGROUND:We aimed to investigate the association between blood urea nitrogen to creatinine ratio (BCR) and survival with favourable neurological outcomes in patients with out-of-hospital cardiac arrest (OHCA). METHODS:This prospective, multicentre, observational study conducted in Osaka, Japan enrolled consecutive OHCA patients transported to 16 participating institutions from 2012 through 2019. We included adult patients with non-traumatic OHCA who achieved a return of spontaneous circulation and whose blood urea nitrogen and creatinine levels on hospital arrival were available. Based on BCR values, they were divided into: 'low BCR' (BCR <10), 'normal BCR' (10 ≤ BCR < 20), 'high BCR' (20 ≤ BCR < 30), and 'very high BCR' (BCR ≥ 30). We evaluated the association between BCR values and neurologically favourable outcomes, defined as cerebral performance category score of 1 or 2 at one month after OHCA. RESULTS:Among 4415 eligible patients, the 'normal BCR' group had the highest favourable neurological outcome [19.4 % (461/2372)], followed by 'high BCR' [12.5 % (141/1127)], 'low BCR' [11.2 % (50/445)], and 'very high BCR' groups [6.6 % (31/471)]. In the multivariable analysis, adjusted odds ratios for 'low BCR', 'high BCR', and 'very high BCR' compared with 'normal BCR' for favourable neurological outcomes were 0.58 [95 % confidence interval (CI 0.37-0.91)], 0.70 (95 % CI 0.49-0.99), and 0.40 (95 % CI 0.21-0.76), respectively. Cubic spline analysis indicated that the association between BCR and favourable neurological outcomes was non-linear (p for non-linearity = 0.003). In subgroup analysis, there was an interaction between the aetiology of arrest and BCR in neurological outcome (p for interaction <0.001); favourable neurological outcome of cardiogenic OHCA patients was lower when the BCR was higher or lower, but not in non-cardiogenic OHCA patients. CONCLUSIONS:Both higher and lower BCR were associated with poor neurological outcomes compared to normal BCR, especially in cardiogenic OHCA patients.