Brain oxygen tension monitoring following penetrating ballistic-like brain injury in rats

Abstract

While brain oxygen tension (PbtO2) monitoring is an important parameter for evaluating injury severity and therapeutic efficiency in severe traumatic brain injury (TBI) patients, many factors affect the monitoring. The goal of this study was to identify the effects of FiO2 (fraction of inspired oxygen) on PbtO2 in uninjured anesthetized rats and measure the changes in PbtO2 following penetrating ballistic-like brain injury (PBBI). Continuous PbtO2 monitoring in uninjured anesthetized rats showed that PbtO2 response was positively correlated with FiO2 (0.21–0.35) but PbtO2 remained stable when FiO2 was maintained at ∼0.26. Importantly, although increasing FiO2 from 0.21 to 0.35 improved PaO2, it concomitantly reduced pH levels and elevated PaCO2 values out of the normal range. However, when the FiO2 was maintained between 0.26 and 0.30, the pH and PaO2 levels remained within the normal or clinically acceptable range. In PBBI rats, PbtO2 was significantly reduced by ∼40% (16.9±1.2mmHg) in the peri-lesional region immediately following unilateral, frontal 10% PBBI compared to sham rats (28.6±1.7mmHg; mean±SEM, p<0.05) and the PBBI-induced reductions in PbtO2 were sustained for at least 150min post-PBBI. Collectively, these results demonstrate that FiO2 affects PbtO2 and that PBBI produces acute and sustained hypoxia in the peri-lesional region of the brain injury. This study provides important information for the management of PbtO2 monitoring in this brain injury model and may offer insight for therapeutic strategies targeted to improve the hypoxia/ischemia state in the penetrating-type brain injury.