THE RELATIONSHIP OF FLUID BALANCE AND SODIUM ADMINISTRATION TO CEREBRAL EDEMA FORMATION AND INTRACRANIAL-PRESSURE IN A PORCINE MODEL OF BRAIN INJURY

Background: Fluid and sodium restriction have been advocated after bra in injury as a means of controlling intracranial pressure (ICP). Recen t clinical data showing no significant relationships between the amoun t of fluid infused or sodium administered (Na) and ICP question this p ractice. Objective: To analyze the relationship of amount of fluid, Na , and fluid balance to cerebral edema formation and ICP. Methods: A cr yogenic brain injury with and without hemorrhagic shock was studied af ter 24 hours in swine (n = 35) randomized to receive either lactated R inger's solution (LR) or hypertonic sodium lactate (HSL). Cerebral ede ma formation as indicated by cortical water content (CWC) was determin ed by measurement of specific gravity. Results: There was a significan t positive correlation between the following variables: (1) amount of fluid and ICP (r = 0.598; p < 0.01); (2) fluid balance and ICP (r = 0. 684; p < 0.01); and (3) free water and ICP (r = 0.614; p < 0.01). Ther e was a significant negative correlation between serum osmolarity and ICP (r = -0.654; p < 0.01). The study failed to demonstrate a signific ant correlation between Na and ICP, amount of fluid and CWC, or fluid balance and CWC. Conclusions: These data suggest that both the volume of fluid infused and the fluid balance do affect the ICP, but the amou nt of Na infused does not. The lack of a significant correlation betwe en any of the independent variables and CWC suggests that their effect on ICP is not related to cerebral edema formation. These findings, co mbined with the observed significant positive correlation between free H2O infused and ICP, and the significant negative correlation between serum osmolarity and ICP, suggest that HSL resuscitation increases in tracranial compliance after brain injury while LR decreases it, The da ta also suggest that free water restriction is warranted in patients w ith head injuries.