Factors associated with neurological outcomes in patients experiencing out-of-hospital cardiac arrest and severe acidaemia: retrospective analysis of a nation-wide registry

Background and objective: Acidaemia is common among individuals who experience out-of-hospital cardiac arrest (OHCA). While severe acidaemia is a strong predictor of unfavourable outcomes, a subset of patients exhibits dramatic recovery. Despite these conflicting outcomes, little is known about the factors associated with neurological outcomes in those who experience OHCA with severe acidaemia.

Methods: This retrospective analysis used data from a Japanese multicentre nationwide database, the Japanese Association for Acute Medicine OHCA Registry. The analysis included data from adult patients with OHCA for whom blood pH data were available upon arrival to hospital. The primary outcome was 30-day survival with favourable neurological outcomes, defined as a Glasgow-Pittsburgh cerebral performance category score of 1 or 2. Patients were categorised with severe acidaemia if their blood pH was ≤ 6.8. Factors associated with favourable outcomes were investigated using multiple logistic regression analysis.

Results: Data from 49,044 patients were included in the analysis, of whom 16,620 exhibited severe acidaemia with a median pH of 6.70 (interquartile range [IQR] 6.61-6.76], and 0.5% (86/16,620) experienced a neurologically favourable outcome. After adjustment for important prognostic factors, witnessed status exhibited a strong association with favourable neurological outcome (adjusted odds ratio [aOR] 6.46 [95% confidence interval (CI) 2.64-15.8]), while initial blood pH exhibited no significant association (aOR 0.90 with every 0.1 unit increase [95% CI 0.71-1.14]).

Conclusion: Although the number is small, a notable number of patients with severe acidaemia exhibited good neurological recovery. Witness status was critical for the prognosis of these patients.