Association between base excess level at hospital arrival and neurological outcomes of adult out-of-hospital cardiac arrest: A multicentre cohort study

Background Cardiac arrest leads to an abrupt cessation of blood flow, resulting in severe metabolic acidosis. Base excess (BE) is a widely used marker of metabolic acidosis. However, its prognostic value in cardiac arrest patients remains unclear, as previous studies have not adjusted for the time from arrest to blood testing. This study aimed to assess the association between BE levels and neurological outcomes in patients with out-of-hospital cardiac arrest (OHCA) by adjusting the time from the onset of cardiac arrest to blood tests. Methods This study in Osaka, Japan, enrolled consecutive patients with OHCA transported to 16 centres between 2012 and 2021. We included adult patients (age ≥ 18 years) with witnessed OHCA and available BE levels upon hospital arrival. The patients were grouped based on BE quartiles: Q1 (BE ≤ − 21.1 mmol/L), Q2 (− 21.1 < BE ≤ − 15.7 mmol/L), Q3 (− 15.7 < BE ≤ − 10.4 mmol/L), and Q4 (BE > − 10.4 mmol/L). The primary outcome was 1-month survival with favourable neurological outcomes, defined as a Cerebral Performance Category scale score of 1 or 2. Results Of the 23,854 patients with OHCA, 7,591 met the inclusion criteria, and 6,066 were eligible for analysis. The 1-month favourable neurological outcomes based on BE quartile were 23.5%, 9.8%, 4.7%, and 3.2% Q4, Q3, Q2, and Q1, respectively (p for trend < 0.001). The adjusted odds ratio for Q1 compared with Q4 was 0.13 (95%CI: 0.090–0.19). Subgroup analysis showed an interaction between prehospital return of spontaneous circulation (ROSC) and outcome (p for interaction < 0.001); neurological outcomes worsened as BE decreased in those with ROSC (p for trend < 0.001), but not in those without ROSC (p for trend = 0.12). Conclusions Lower BE levels upon hospital arrival are associated with worse neurological outcomes and may serve as prognostic indicators, especially in patients with OHCA and prehospital ROSC.