Retraction induced brain edema.

A local cerebral retraction apparatus which simulates cerebral retraction was devised in an effort to clarify the relationship among the retraction pressure, somatosensory evoked potential (SEP) and cerebral blood flow (CBF) by measuring these parameters both simultaneously and chronologically. Twenty seven cats were divided into three groups according to the retraction pressure (10,30 and 50 mmHg, respectively). Each group underwent 30 minutes' retraction. At a retraction pressure of 10 mmHg, the reduction rate of CBF was low and the recovery of SEP was excellent. With an excessive pressure of 50 mmHg, both SEP and CBF reduced to 60% of the control value during the retraction and the recovery of SEP was extremely poor. Marked hyperemia of the brain surface was seen immediately after the release of retraction in more than 50% of the animals. At 30 mmHg, the recovery of SEP was moderately disturbed but, nevertheless, with a satisfactory value of more than 60% of the control. When the N1 component of SEP was abolished, the residual CBF showed approximately 60% of the control value, which seemed relatively high as compared to cases where cerebral artery were occluded. Extravasation of Evans blue which is an indication of vasogenic brain edema due to disruption of the blood-brain barrier, occurred extensively in the cerebral cortex involving a deep-lying white matter and an increase of the retraction pressure, corresponding to a poor recovery of neuronal function.