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

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 P_aO₂, it concomitantly reduced pH levels and elevated P_aCO₂ values out of the normal range. However, when the FiO₂ was maintained between 0.26 and 0.30, the pH and P_aO₂ levels remained within the normal or clinically acceptable range. In PBBI rats, PbtO₂ was significantly reduced by ∼40% (16.9 ± 1.2 mmHg) in the peri-lesional region immediately following unilateral, frontal 10% PBBI compared to sham rats (28.6 ± 1.7 mmHg; mean ± SEM, p < 0.05) and the PBBI-induced reductions in PbtO₂ were sustained for at least 150 min 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.