The impact of hypercarbia on the evolution of brain injury in a porcine model of traumatic brain injury and systemic hemorrhage

Carbon dioxide is perhaps the most potent available modulator of cerebrovas cular tone and thus cerebral blood flow (CBF). These experiments evaluate t he impact of induced hypercarbia on the matching of blood flow and metaboli sm in the injured brain. We explore the hypothesis that hypercarbia will re store the relationship of CBF to metabolic demand, resulting in improved ou tcome following traumatic brain injury (TBI) and hemorrhage, A behavioral o utcome score, hemodynamic, metabolic, and pathologic parameters were assess ed in anesthetized and ventilated juvenile pigs, Animals were assigned to e ither normocarbia or hypercarbia and subdivided into TBI (via fluid percuss ion) with or without hemorrhage, The experimental groups were TBI; TBI + 40 % hemorrhage (40%H); TBI + hypercarbia (CO2); and TBI + 40%H + CO2. Hemorrh aged animals were resuscitated with blood and crystalloid, Hypercarbia was induced immediately following TBI using 10% FiCO(2). The normocarbic group demonstrated disturbance of the matching of CBF to metabolism evidenced by statistically significant increases in cerebral oxygen and glucose extracti on. Hypercarbic animals showed falls in the same parameters, demonstrating improvement in the matching of CBF to metabolic demand. Parenchymal injury was significantly decreased in hypercarbic animals: 3/10 hypercarbic versus 6/8 normocarbic animals showed cerebral contusions at the gray/white inter face (p = 0.05). The hypercarbic group had significantly better behavioral outcome scores, 10.5, versus 7.3 for the normocarbic groups (p = 0.005). Th e decreased incidence of cerebral contusion and improved behavioral outcome scores in our experiments appear to be mediated by better matching of cere bral metabolism and blood flow, suggesting that manipulations modulating th e balance of blood flow and metabolism in injured brain may improve outcome s from TBI.