BRAIN EDEMA FORMATION AFTER BRAIN INJURY, SHOCK, AND RESUSCITATION - EFFECTS OF VENOUS AND ARTERIAL-PRESSURE

Background: Recent work suggests that increased intracranial pressure (ICP) following brain injury and shock is related to increased central venous pressure (CVP) following resuscitation. Objective: To analyze the relationship of intravascular pressures to edema formation and ICP in an experimental model. Methods: In a porcine model of cryogenic br ain injury and hemorrhagic shock, we studied CVP, mean arterial pressu re (MAP), ICP, and cortical water content (CWC, as cortical specific g ravity) at baseline (BL), 45 minutes after shock (H45), and 1, 3, 6, 1 2, and 24 hours (H) after resuscitation. Group 1 was the control group , group 2 brain injury only, group 3 shock only, and group 4 brain inj ury and shock. Results: Brain injury significantly increased ICP and C WC. Mean arterial pressure significantly correlated with ICP (r = 0.54 , p = 0.02) and with CWC (r = -0.48, p = 0.03) in group 4 at 24H but n ot in the other groups at any time period. There was no significant co rrelation between CVP and ICP or CWC in any group at any time interval . Conclusions: These data suggest that brain edema formation in the in jured hemisphere is related to MAP and not CVP, but variability in MAP accounts for only 29% of the variability in CWC and ICP, suggesting t he importance of factors other than hydrostatic pressure in determinin g the amount of edema and the ICP after brain injury. Previous work de monstrating the significant correlation of polymorphonuclear leukocyte infiltration with ICP (r = 0.71, p < 0.001) and with CWC (r = -0.63, p < 0.001) suggests that inflammation may be one of these factors.