Optic nerve sheath diameter and Pcv-aCO₂/Ca-cvO₂ for predicting outcomes in traumatic brain injury patients during prehospital care: a prospective cohort study in China.

Abstract

To predict the outcome of patients with traumatic brain injury (TBI) using the optic nerve sheath diameter (ONSD) and the central venous minus arterial CO₂ pressure to arterial minus central venous O₂ content ratio (Pcv-aCO₂/Ca-cvO₂) in prehospital settings. A prospective cohort study was conducted in China. The study was conducted from October 2023 to October 2024, enrolling patients diagnosed with TBI. Participants presenting a Glasgow Coma Scale (GCS) <8 at initial assessment were included in the research. Patients were classified into four groups according to ONSD and Pcv-aCO₂/Ca-cvO₂: Group A Pcv-aCO₂/Ca-cvO₂ >1.8 mm Hg/mL and ONSD >5.6 mm; Group B: Pcv-aCO₂/Ca-cvO₂ >1.8 mm Hg/mL and ONSD ≤5.6 mm; Group C: Pcv-aCO₂/Ca-cvO₂ ≤1.8 mm Hg/mL and ONSD >5.6 mm; and Group D: Pcv-aCO₂/Ca-cvO₂ ≤1.8 mm Hg/mL and ONSD ≤5.6 mm. 30-day mortality, functional neurological recovery at discharge (measured by Glasgow Outcome Scale (GOS)), and length of intensive care unit (ICU) stay were compared between the 4 groups. Our findings show that Group D had the lowest 30-day mortality, the shortest ICU stay and the highest good recovery at discharge (GOS score) among the four groups. Survival curves illustrated a decrease in 30-day mortality in group C patients after mannitol administration compared with patients who did not receive mannitol administration. The area under the receiver operating characteristic curve for Pcv-aCO₂/Ca-cvO₂ combined with ONSD (0.907 (95% CI 0.843 to 0.941)) was higher than those for ONSD (0.851 (95% CI 0.791 to 0.911)) alone, Pcv-aCO₂/Ca-cvO₂ (0.814 (95% CI 0.744 to 0.873)) alone or initial GCS (0.823 (95% CI 0.763 to 0.889)). Calibration plots demonstrated a strong alignment between observed and predicted probabilities for ONSD, Pcv-aCO₂/Ca-cvO₂, the combination of ONSD and Pcv-aCO_₂/Ca-cvO_₂, and initial GCS. ONSD combined with Pcv-aCO₂/Ca-cvO₂ is a relatively novel method for predicting the outcome in TBI patients, especially in a prehospital setting. This dual approach may improve the prediction of early prognosis and guide osmotherapy treatment in patients with TBI.