INCREASED FREE-RADICAL PRODUCTION DUE TO SUBDURAL-HEMATOMA IN THE RAT- EFFECT OF INCREASED INSPIRED OXYGEN FRACTION

Acute subdural hematoma (ASDH) complicates about 15%-20% of severe hea d injury patients and is one of the major causes for bad outcome, yet the pathomechanisms involved are not well understood. This study has e mployed a recently developed technique to determine whether ASDH induc es free radicals in the underlying brain. We also studied the effect o f increased inspired oxygen fraction (FiO(2)) on free radical producti on, both in the normal rat brain and after ASDH induction. Twelve male Sprague Dawley rats were studied over 5 h (2 h of FiO(2) = 30%, 3 h o f FiO(2) = 100%). Hydroxyl radical production was measured with microd ialysis using the salicylate trapping technique by quantitating the 2, 3 dihydroxy benzoic acid (2,3 DHBA) and 2,5 dihydroxy benzoic acid (2, 5 DHBA), degradation products, in either noninjured brain (n = 6) or a fter ASDH tit = 6). Both 2,3 DHBA and 2,5 DHBA increased significantly by 39% and 108%, respectively, after the induction of the SDH (p < 0. 05). By increasing the FiO(2) to 100%,2 h after ASDH induction, the 2, 3 DHBA and 2,5 DHBA further increased only slightly (ns). After increa sing the FiO(2) to 100% in the noninjured group, the mean level of 2,3 DHBA increased by 56% (p = 0.06, ns). The level of 2,5 DHBA in the di alysate increased significantly by 56% (p < 0.05), when the FiO(2) was increased to 100% ASDH results in a significant increase in free radi cal production. At the same time, prolonged increase in FiO(2) does no t lead to further increase in free radical production in the injured b rain.