INFLUENCE OF ISOFLURANE, FENTANYL, THIOPENTAL, AND ALPHA-CHLORALOSE ON FORMATION OF BRAIN EDEMA RESULTING FROM A FOCAL CRYOGENIC LESION

The objective of this study was to analyze the effects of various anes thetics on the formation of brain edema resulting from a focal cryogen ic lesion. Thirty rabbits (six per group) were anesthetized with isofl urane (1 minimum alveolar anesthetic concentration [MAC] 2.1 vol%), fe ntanyl (bolus 5 mu g/kg; infusion rate 1.0-0.5 mu g . kg(-1). min(-1)) , thiopental (32.5 mg . kg(-1). h(-1)), or alpha-chloralose (50 mg/kg) . Control animals (sham operation, no lesion) received alpha-chloralos e (50 mg/kg). Regional cerebral blood flow (rCBF) in perifocal brain t issue was measured by H-2-clearance. Animals anesthetized with isoflur ane required support of arterial pressure by angiotensin II (0.15 mu g . kg(-1). min(-1)). Six hours after trauma the animals were killed. F ormation of brain edema was studied by specific gravity of cortical gr ay matter, white matter, hippocampus, caudate nucleus, putamen, and th alamus. Brain tissue samples were collected at multiple sites close to and distant from the lesion. Mean arterial pressure, arterial Pco(2) and Po-2, hematocrit, body temperature, and blood glucose were not dif ferent between groups during the posttraumatic course (except for an i ncreased arterial pressure with alpha-chloralose compared to thiopenta l 4-6 h after trauma). The specific gravity of cortical gray matter wa s significantly reduced up to a distance of 6 mm from the center of th e lesion in animals anesthetized with isoflurane, thiopental, or alpha -chloralose and up to 9 mm in animals given fentanyl. In white matter, vasogenic edema extended up to 12 mm from the lesion focus in animals anesthetized with fentanyl, thiopental, or alpha-chloralose. In isofl urane-anesthetized animals, white matter samples in all regions were s imilar to control. The specific gravity in hippocampus, caudate nucleu s, putamen, or thalamus was not altered as compared to the controls. r CBF studied before cryogenic injury had a range of 37-44 mL . 100 g(-1 ). min(-1), except in animals given fentanyl (i.e., 59.9 mL . 100 g(-1 ). min(-1)). During the first 3 h af ter trauma, animals given fentany l had significantly higher rCBF values than animals with thiopental or the controls. At 4-6 h after trauma, rCBF was decreased in animals wi th fentanyl or thiopental as compared to the baseline level, although differences were not observed between groups. Regression analyses of d ata from all experimental groups do not reveal a relationship between the formation of posttraumatic brain edema and mean arterial pressure or rCBF. We conclude that isoflurane anesthesia attenuates cerebral ed ema from a standard cerebral lesion as compared to fentanyl, thiopenta l, or alpha-chloralose.