Newborn resuscitation: should we oxygenate or not?

Abstract

HOW SHOULD WE OXYGENATE newborn and infants suffering from hypoxia and ischemia? Is it harmful to use 100% O 2 ? It may seem odd to question a practice that has been carried out for so long, seemingly without any adverse effects. The case is, however, that after the practice of routinely using 100% O 2 for newborn resuscitation was examined, many serious potentially harmful effects have to date been described (for review, see Ref. 13).Fabian et al.(1) add new information to the topic of how asphyxiated newborns should be reoxygenated (1). By inducing unilateral brain ischemia and hypoxia in newborn (7 day) rats, they showed that cerebral blood flow in the ischemic cortex declined following resuscitation with 100% O 2 but not with ambient air. These findings in hyperoxic animals were accompanied by a reduction in perivascular production of nitric oxide (NO). Intraperitoneal injection with tetrahydrobiopterin (BH 4 ) increased cerebral blood flow during hyperoxic resuscitation. This was followed by increased perivascular NO and reduced perivascular O 2 Ϫ . The authors suggest that hyperoxia uncouples perivascular NO synthase (NOS), probably endothelial NOS, leading to a reduced NO and increased O 2 Ϫ production. An injection of apocyanin, which is an inhibitor of NADPH oxidase, also increased NO and reduced O 2 Ϫ , indicating that an oxidative burst may be of importance in neonatal hypoxic-ischemic brain injury.This study confirms that a hyperoxic resuscitation of newborns may reduce the restoration of cerebral blood flow and therefore may be detrimental. But it also indicates that BH 4 and perhaps also apocyanin should be interesting agents to test out in similar models to prevent such potentially harmful effects.For many reasons one should be careful drawing firm conclusions from newborn rats to newborn human infants. One major difference between birth asphyxia and the present model is that in the former the partial carbon dioxide tension of arterial blood (PaCO 2 ) is elevated. Restoration of cerebral blood flow during reoxygenation differs whether it starts out with a high or as in the present study a relatively low PaCO 2 (16). In resuscitated newborns infants, we also know that the time of reoxygenation often does not last more than a few minutes. A reoxygenation time of 2 h as in the study of Fabian et al. (1) therefore may not be relevant for newborns. On the other hand, such a long exposure to hyperoxia is not rare in the intensive care of children outside the immediate newborn period. A recent study by Koch et al. (8) showed that postischemic and posthypoxic hyperoxic exposure may have shocking effects on the brain. These authors found a dramatic augmented cerebral injury in 2-wk-old mice exposed to unilateral carotid ligation and hypoxia already after 30 min of hyperoxic-reoxygenation compared with reoxygenation with ambient air.

Normabaric Hyperoxia Treatment Improved Locomotor Activity of C57BL/6J Mice through Enhancing Dopamine Genes Following Fluid-Percussion Injury in Striatum

“…Ultimately, this leads to hypoxic-ischemic injury as a result of inadequate oxygen supply to the brain tissue. As result, brain tissue oxygen tension would be increased (38). In our current experiment, the results suggested that locomotor activity of mice were gradually improved in Normabaric hyperoxia treated animals as compared to injured animals without treatment.…”