Association of abnormal carbon dioxide levels with poor neurological outcomes in aneurysmal subarachnoid hemorrhage: a retrospective observational study.

Background: In patients with aneurysmal subarachnoid hemorrhage (SAH), an association between hypocapnia and poor clinical outcomes has been reported. However, the optimal arterial carbon dioxide tension (PaCO2 ) remains unknown. The present retrospective study aimed to examine the association of abnormal PaCO2 levels with neurological outcomes and investigate the optimal target PaCO2 level in patients with SAH.

Methods: We retrospectively selected consecutive adult patients hospitalized in the intensive care unit (ICU) for SAH between January 2009 and April 2017. Univariate and multivariate analyses were performed to identify the independent predictors of unfavorable neurological outcomes (i.e., modified Rankin scale score of 3-6 on hospital discharge).

Results: Among 158 patients with SAH, 73 had unfavorable neurological outcomes. During the first 2 weeks in the ICU, the median number of PaCO2 measurements per patient was 43. The factors significantly associated with unfavorable neurological outcomes were age, Hunt and Kosnik grade, maximum lactate levels during the first 24 h, and maximum (odds ratio [OR], 1.12; 95% confidence interval [CI], 1.03-1.21; p  < 0.01) and minimum PaCO2 levels (OR, 0.81; 95% CI, 0.72-0.92; p  < 0.01). Receiver operating characteristic curve analysis revealed that the cutoff range of PaCO2 was 30.2-48.3 mmHg. Unfavorable neurological outcomes were noted in 78.8% of patients with PaCO2 levels outside this range and in 22.8% of patients with PaCO2 levels within this range.

Conclusions: Both the maximum and minimum PaCO2 levels during ICU management in patients with SAH were significantly associated with unfavorable neurological outcomes. Further prospective studies are required to validate our findings and explore their clinical implications. Our findings may provide a scientific rationale for these future prospective studies.