FAILURE OF NORMOBARIC OXYGEN-THERAPY TO REDUCE ISCHEMIC BRAIN-DAMAGE IN RATS

We investigated the effects of 24-h oxygen therapy on focal cerebral i schemia in rats. Under halothane anesthesia, a 3-0 nylon thread was in troduced into the neck internal carotid artery to occlude the left mid dle cerebral artery (MCA). Under atmospheric pressure, group 1 animals inhaled standard air; group 2, 40% O-2; group 3, 60% O-2; and group 4 , 100% O-2. Neuropathologic outcomes were quantified after a 24-h inha lation period. Infarct volumes tended to decrease in groups 2-4, but t he decreases were not significant when compared with group 1. Hemisphe ric volume differences of groups 2-4 (27 +/- 18 mm(3), 22 +/- 17 mm(3) , and 31 +/- 22 mm(3), respectively) were less than that of group 1 (6 1 +/- 23 mm(3), P < 0.05). Our results demonstrate that O-2 therapy re duces brain swelling in rats 24 h after MCA occlusion. However, a dose -dependent decrease in brain swelling was not observed. In addition, w e failed to see a significant decrease in the infarct size.