Resuscitation of the newborn – with or without supplemental oxygen? : An experimental study in newborn piglets

2-5% of babies born at term are in need of resuscitation, some of them as a result of birth asphyxia. The use of high oxygen concentration for resuscitation has been questioned. Both animal and human studies have indicated that newborns can be reoxygenated as efficiently with 21% as 100% oxygen. The purpose of the current thesis has been to test if this would apply when we changed the piglet model from global hypoxemia alone to combined cerebral hypoxemia-ischemia, and then to combined cerebral hypoxemia-ischemia-hypercapnia. A total of 103 1-3-day-old piglets were included. When piglets were reoxygenated with 21% or 100% oxygen following combined cerebral hypoxemia-ischemia, significantly higher blood pressure and more complete restoration of cerebral microcirculation (laser Doppler flow) and biochemical markers (microdialysis) were found after reoxygenation with 100% oxygen compared to room air (microcirculation in cerebral cortex 100% of baseline values after 2 hours in the 100% oxygen group compared to 30% of baseline in the room air group). This is in contrast to findings in a piglet model of hypoxemia alone. When moderate hypercapnia was added during the insult, significantly higher blood pressure and more complete restoration of microcirculation in the cerebral cortex (but not in the striatum) were still found in the 100% oxygen group compared with the room air group. But the differences were less pronounced, and there were no significant differences in biochemical markers, a finding which suggested that the brain tolerated reoxygenation with room air as well as 100% oxygen in this model. The added hypercapnia during the insult probably served to protect the brain. A single intravenous dose of the antioxidant enzyme superoxide dismutase given after the insult did not influence on cerebral microcirculation or biochemical markers. Reoxygenation with 100% oxygen for only 5 min was as efficient as 20 min compared with room air. This thesis has shown that in a piglet model of birth asphyxia, exposure to 100% oxygen during initial reoxygenation can be of benefit in restoring cerebral microcirculation and blood pressure, especially if the insult is severe