Comparative studies of edema produced by fluid percussion injury with lateral and central modes of injury in cats.

Earlier studies by our laboratories indicated that severe fluid percussion injury in cats results in the development of significant brain edema. In this study we measured the spatial distribution of edema developed after both central and lateral modes of impact with the objective of determining the degree to which the edema volume may contribute to ICP elevation and neurologic deterioration. All animals developed a marked increase in tissue water, particularly in the brainstem. In laterally injured cats, the increase in brainstem water equaled the edema produced supratentorially. Adding the increase of brainstem edema and the edema volume of the supratentorial compartment, we found an average water increase of 1.125 cc in survivors and 2.492 cc in nonsurvivors. This represents a significant volume increase when it is considered that the average PVI of the normal cat is approximately 0.9 cc (6). However, we observed that the PVI was reduced soon after injury and at a time when it has been reported that water content was near normal levels (7). Taking these studies in concert, we believe that the early reduction in PVI is most probably due to vascular swelling. The developing edema further contributes to reductions in PVI, thus setting the stage for elevated ICP and the tissue impaction observed in nonsurvivors.