EFFECT OF LESION VOLUME ON CEREBRAL HEMODYNAMICS AFTER FOCAL BRAIN INJURY AND SHOCK

Cerebral blood flow (CBF) varies unpredictably in patients after head injury and hemorrhagic shock. Proper treatment requires knowledge of i schemic versus hyperemic flow. The degree to which the size or severit y of the injury may contribute to CBF abnormalities is unknown. We hyp othesized that lesion size is a determinant of postinjury CBF. We meas ured cerebral and systemic variables in a porcine model of focal cryog enic brain injury and hemorrhagic shock over a 5-hour period. Swine we re randomized to receive either a large or small lesion followed by he morrhage. In the small lesion group traumatic brain injury, followed b y shock and resuscitation, produced a significant and sustained elevat ion in bihemispheric regional CBF and cerebral oxygen delivery that wa s significantly greater than that observed in either the large lesion group or the controls (p < 0.05). There were no significant difference s between the experimental groups in volume of hemorrhage, intracrania l pressure, cerebral perfusion pressure, arterial oxygen content, or P aCO2. These data suggest that the volume of injured tissue may determi ne post-resuscitation CBF, and that interventions to reduce cerebral b lood volume (i.e., hyperventilation) may not be universally applicable in all head injured patients.