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 head injury patients and is one of the major causes for bad outcome, yet the pathomechanisms involved are not well understood. This study has employed a recently developed technique to determine whether ASDH induces free radicals in the underlying brain. We also studied the effect of increased inspired oxygen fraction (FiO(2)) on free radical production, 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 of FiO(2) = 100%). Hydroxyl radical production was measured with microdialysis 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 after 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 increasing 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 dialysate increased significantly by 56% (p < 0.05), when the FiO(2) was increased to 100% ASDH results in a significant increase in free radical production. At the same time, prolonged increase in FiO(2) does not lead to further increase in free radical production in the injured brain.