Hyperbaric oxygen after global cerebral ischemia in rabbits does not promote brain lipid peroxidation

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Abstract
Objective To determine whether hyperbaric oxygen administered immediately after global cerebral ischemia increases free radical generation and lipid peroxidation in the brain or alters neurophysiologic recovery. Design Prospective, randomized, controlled trial. Setting Animal research laboratory. Subjects Adult male New Zealand white rabbits. Interventions Anesthetized rabbits were subjected to 10 mins of global cerebral ischemia by infusing a mock cerebrospinal fluid into the subarachnoid space and increasing intracranial pressure equal to mean arterial pressure. Immediately upon reperfusion, one group of rabbits (n = 9) was treated with hyperbaric oxygen at 2.8 atmospheres absolute for 75 mins while the control group (n = 9) breathed room air for an equivalent period of time. At the end of the reperfusion period, oxyradical brain damage was determined by measuring brain levels of oxidized and total glutathione and free malondialdehyde. Neurophysiologic brain injury was assessed with cortical somatosensory evoked potentials. Measurements and Main Results Both oxidized glutathione and the ratio of oxidized glutathione to reduced glutathione (total minus oxidized) were higher (p < .05) in the hyperbaric oxygen group, indicating that hyperbaric oxygen increased free radical generation. Nonetheless, brain malondialdehyde content, an index of lipid peroxidation, was similar (p > .05) in the two groups. Cortical somatosensory evoked potential recovery at the end of reperfusion was 50% higher (p < .05) in the hyperbaric oxygen-treated animals compared with controls. Conclusions Treatment with hyperbaric oxygen after ischemia increased the amount of oxygen free radicals in the brain. However, this increase in free radical generation was not associated with an increase in lipid peroxidation or a reduction in neurophysiologic recovery when measured after 75 mins of recirculation. These results suggest that hyperbaric oxygen administered immediately after global ischemia does not promote early brain injury. (Crit Care Med 1995; 23:1398-1404)