Cerebral Perfusion Pressure Directed Therapy Following Traumatic Brain Injury and Hypotension in Swine

There is a paucity of studies, clinical and experimental, attesting to the benefit of cerebral perfusion pressure (CPP) directed pressor therapy following traumatic brain injury (TBI). The current study evaluates this therapy in a swine model of TBI and hypotension. Forty-five anesthetized and ventilated swine received TBI followed by a 45% blood volume bleed. After 1 h, all animals were resuscitated with 0.9% sodium chloride equal to three times the shed blood volume. The experimental group (PHE) received phenylephrine to maintain CPP \u3e 80 mm Hg; the control group (SAL) did not. Outcomes in the first phase (n = 33) of the study were as follows: cerebro-venous oxygen saturation (S cvO2), cerebro-vascular carbon dioxide reactivity (δScvO2), and brain structural damage (β-amyloid precursor protein [βAPP] immunoreactivity). In the second phase (n = 12) of the study, extravascular blood free water (EVBFW) was measured in the brain and lung. After resuscitation, intracranial and mean arterial pressures were \u3e15 and \u3e80 mm Hg, respectively, in both groups. CPP declined to 64 ± 5 mm Hg in the SAL group, despite fluid supplements. CPP was maintained at \u3e80 mm Hg with pressors in the PHE group. PHE animals maintained better ScvO2 (p \u3c 0.05 at 180, 210, 240, 270, and 300 min post-TBI). At baseline, 5% CO2 evoked a 16 ± 4% increase in ScvO2, indicating cerebral vasodilatation and luxury perfusion. By 240 min, this response was absent in SAL animals and preserved in PHE animals (p \u3c 0.05). Brain EVBFW was higher in SAL animals; however, lung EVBFW was higher in PHE animals. There was no difference in βAPP immunoreactivity between the SAL and PHE groups (p \u3e 0.05). In this swine model of TBI and hypotension, CPP directed pressor therapy improved brain oxygenation and maintained cerebro-vascular CO2 reactivity. Brain edema was lower, but lung edema was greater, suggesting a higher propensity for pulmonary complications