The Hx-xanthine oxidase system is assumed to be an important oxygen radical generating system. Previous studies have shown that there were no differences between resuscitation with 21% vs. 100% O2 concerning Hx levels in arterial plasma or rate of normalizing of base deficit and pH. The present study compared the effect of 21% vs. 100% O2 during posthypoxic resuscitation on Hx levels in cerebral cortex and femoral muscle. Extracellular levels of Hx were determined by in vivo microdialysis.Methods: Studies were performed in 26 anesthetized, ventilated and instrumented newborn piglets. After a one-hour baseline period the piglets were randomly divided into 3 groups: group 1 (normoxia, n=8), group 2(hypoxia, FiO2 = 0.08, followed by resuscitation with 21% O2, n=9) and group 3 (hypoxia, followed by resuscitation with 100% O2 in 30 min, further resuscitation with 21% O2, n=9). When mean arterial blood pressure fell below 20 mm Hg, reoxygenation was started. PaCO2 was kept in normal range throughout the experiment. Results: Lowest pH of 6.91 ± 0.11(group 2, mean ± SD) and 6.90 ± 0.07(group 3, mean ± SD) were reached at the end of hypoxia and then normalized over the following 3 hours. There were no statistical differences between group 2 and 3 throughout the experiment concerning hypoxic time, blood pressure, pH, base deficit, hematocrit or plasma Hx. During the resuscitation with 100% O2, a significant higher content of Hx was found in the brain cortex compared with resuscitation with 21% O2. In muscle, however, we did not find any statistical difference between the groups. Conclusion: These data indicate that brain cell purine metabolism is impaired when resuscitating with 100% O2 compared with 21% O2. This may aggravate neuronal posthypoxic reoxygenation injury.Figure

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Figure 1