End-tidal carbon dioxide and arterial to end-tidal carbon dioxide gradient are associated with mortality in patients with neurological injuries.

Pre-hospital end-tidal carbon dioxide (ECO) monitoring and arterial to end-tidal carbon dioxide gradient (PCO) have been associated with mortality in patients with traumatic brain injury. Our study aimed to analyze the association between alveolar ECO or PCO and mortality in patients admitted in intensive care unit (ICU) with neurological injuries. In our retrospective analysis from using large de-identified ICU databases (MIMIC-III and -IV and eICU databases), we included 2872 ICU patients with neurological injuries, identified according to the International Classification of Diseases (ICD-9 and -10), who underwent ECO monitoring. We performed logistic regression and extended Cox regression to assess the association between mortality and candidate covariates, including ECO and PCO. In-hospital mortality was 26% (n = 747). In univariate analysis, both the PCO gradient and ECO levels during the first 24 h were significantly associated with mortality (for a 1 mmHg increase: OR = 1.03 [CI 1.016-1.035] and OR = 0.94 [CI 0.923-0.953]; p < 0.001). The association remained significant in multivariate analysis. The time-varying evolution of EtCO was independently associated with mortality (for a 1 mmHg increase: HR = 0.976 [CI 0.966-0.985]; p < 0.001). The time-varying PCO gradient was associated with mortality only in univariate analysis. In neurocritical patients, lower ECO levels at admission and throughout the ICU stay were independently associated with mortality and should be avoided.