The Acute Effects of Hemorrhagic Shock on Cerebral Blood Flow, Brain Tissue Oxygen Tension, and Spreading Depolarization following Penetrating Ballistic-Like Brain Injury

Traumatic brain injury (TBI) often occurs in conjunction with additional trauma, resulting in secondary complications, such as hypotension as a result of blood loss. This study investigated the combined effects of penetrating ballistic-like brain injury (PBBI) and hemorrhagic shock (HS) on physiological parameters, including acute changes in regional cerebral blood flow (rCBF), brain tissue oxygen tension (PbtO2), and cortical spreading depolarizations (CSDs). All recordings were initiated before injury (PBBI/HS/both) and maintained for 2.5 h. Results showed that PBBI alone and combined PBBI and HS produced a sustained impairment of ipsilateral rCBF that decreased by 70% from baseline (p < 0.05). Significant and sustained reductions in PbtO2 (50% baseline; p < 0.05) were also observed in the injured hemisphere of the animals subjected to both PBBI and HS (PBBI + HS). In contrast, PBBI alone produced smaller, more transient reductions in PbtO2 levels. The lower limit of cerebral autoregulation was significantly higher in the PBBI + HS group (p < 0.05, compared to HS alone). Critically, combined injury resulted in twice the number of spontaneous CSDs as in PBBI alone (p < 0.05). It also lowered the propagation speed of CSD and the threshold of CSD occurrence [induced CSD at higher mean arterial pressure (MAP)]. However, rCBF and PbtO2 were not responsive to the depolarizations. Our data suggest that PBBI together with HS causes persistent impairment of CBF and brain tissue oxygen tension, increasing the probability of CSDs that likely contribute to secondary neuropathology and compromise neurological recovery.