Pcv-aCO2/Ca-cvO2 Combined with Optic Nerve Sheath Diameter in Predicting Elevated Intracranial Pressure of Patients with Traumatic Brain Injury in Prehospital Setting.

Purpose: To investigate a correlation between the central venous minus arterial CO₂ pressure to arterial minus central venous O₂ content ratio (Pcv-aCO₂/Ca-cvO₂) combined with optic nerve sheath diameter (ONSD) in predicting prehospital elevated intracranial pressure (ICP) in traumatic brain injury (TBI) patients.

Patients and methods: This was a prospective observational study of all adult TBI patients from the surgical intensive care unit who underwent invasive ICP monitoring between January 2023 and December 2023. Using a Delica MVU-6300 machine with 14-5 MHz linear probe to measure ONSD. We drew blood samples for arterial and central venous blood gases to measure and calculate the following indicators such as Pcv-aCO₂, Ca-cvO₂, and Pcv-aCO₂/Ca-cvO₂ ratio. ONSD and Pcv-aCO₂/Ca-cvO₂ were recorded during the first 3 days after admission. Simultaneous ICP values were gained from the invasive monitoring. Associations between ONSD, Pcv-aCO₂/Ca-cvO₂ and simultaneous ICP were explored by Spearman correlation analysis. We constructed an ROC curve to identify the ONSD and Pcv-aCO₂/Ca-cvO₂ cutoff for the evaluation of elevated ICP.

Results: We included 54 patients aged mean 57.13 (standard deviation 4.02) years and 24 (44%) were male. A significant correlation was observed between ONSD and ICP (r = 0.74, P < 0.01). The AUC was 0.861 (95% CI: 0.727-0.951), with a best cutoff value of 5.62 mm. Using a cutoff of 5.62mm, ONSD had a sensitivity of 92.8%, specificity of 80.4%. The Pcv-aCO₂/Ca-cvO₂ ratio also significantly correlated with ICP (r = 0.70, P < 0.01). The AUC was 0.791 (95% CI: 0.673-0.889). The optimal Pcv-aCO₂/Ca-cvO₂ value for predicting elevated ICP was 1.98 mmHg/mL. Using a cutoff of 1.98 mmHg/mL, Pcv-aCO₂/Ca-cvO₂ had a sensitivity of 87.3%, specificity of 77.2%. The AUC for ONSD combined with Pcv-aCO₂/Ca-cvO₂ was 0.952 (95% CI: 0.869-0.971), which had a sensitivity of 95.1%, specificity of 93.9%.

Conclusion: Pcv-aCO₂/Ca-cvO₂ combined with ONSD performed best in predicting elevated intracranial pressure of patients with TBI in a prehospital setting. Our findings provide a crucial tool to improve earlier management of these patients in prehospital care, where the availability and utilization of invasive monitoring is limited. It could lead to significant changes in how TBI patients are monitored and treated before reaching a hospital.