Resuscitation of the asphyxic newborn infant: new insight leads to new therapeutic possibilities

Hydrogen peroxide differentially affects activity in the pre-Bötzinger complex and hippocampus

Reactive oxygen species (ROS) modulate neuronal excitability. In the present study we examined the effects of hydrogen peroxide (H(2)O(2)), a well established ROS, on neuronal activity from two neonatal mouse brain regions, i.e., the pre-Bötzinger complex (preBötC) within the ventral respiratory column (VRC) and the CA1 area of the hippocampus. In the preBötC, 2.2 mM H(2)O(2) evoked a transient depression followed by augmentation of neuronal activity. The iron chelator deferoxamine (500 μM) did not prevent H(2)O(2)-mediated neuronal augmentation but prevented the initial depression. Combined application of Fe(2+) and H(2)O(2) only caused depression of the preBötC rhythm. In contrast, H(2)O(2) suppressed neuronal activity in the CA1 region, and this effect was accentuated by coapplication of Fe(2+) and H(2)O(2), suggesting that hydroxyl radical generated by Fenton reaction mediates the effects of H(2)O(2) on CA1 neuronal activity. Malondialdehyde (MDA) levels were monitored as an index of lipid peroxidation in H(2)O(2)-treated preBötC and CA1 areas. MDA levels were unaltered in H(2)O(2)-treated preBötC, whereas MDA levels were markedly elevated in the CA1 region. These findings suggest that 1) exogenous administration of H(2)O(2) exerts differential effects on neuronal activities of preBötC versus CA1 neuronal populations and 2) H(2)O(2) is a potent modulator of respiratory rhythmogenesis from the preBötC without affecting global oxidative status.

Oxygen supplementation in the delivery room: updated information

Resuscitation is the most common procedure performed in neonatology. However, new contributions based on scientific evidence challenge the traditional procedures. Of these new contributions, the use of room-air instead of 100% oxygen and titration of the oxygen inspiratory fraction according to oximetry and heart rate represent a new approach in the resuscitation of both term and preterm newborns.

Tyrosine phosphorylation of apoptotic proteins during hyperoxia in mitochondria of the cerebral cortex of newborn piglets

The present study tests the hypothesis that hyperoxia results in increased tyrosine phosphorylation of apoptotic proteins Bcl-2, Bcl-xl, Bax & Bad in the mitochondrial fraction of the cerebral cortex of newborn piglets. Twelve newborn piglets were divided into normoxic [Nx, n = 6], exposed to a FiO(2) of 0.21 for 1 h and hyperoxic [Hyx, n = 6], exposed to FiO(2) of 1.0 for 1 h. PaO(2) in Hyx group was maintained at 400 mmHg while the Nx group was kept at 80 to 100 mmHg. The density (O.D.x mm(2)) of phosphorylated Bcl2 protein on westernblot was 19.3 +/- 3.6 in Nx and 41.5 +/- 18.3 in Hyx, (P < 0.05). The density of phosphorylated Bcl-xl protein density was 26.9 +/- 7.0 in Nx and 47.9 +/- 2.5 in Hyx, (P < 0.05). Phosphorylated Bax density was 43.5 +/- 5.0 in Nx and 43.3 +/- 5.2 in Hyx. Phosphorylated Bad density was 23.6 +/- 3.9 in Nx, 24.4 +/- 4.7 in Hyx. The data show that during hyperoxia there is a significant increase in tyrosine phosphorylation of Bcl2 and Bcl-xl, while the phosphorylation of proapototic proteins Bax & Bad was not altered. We conclude that hyperoxia leads to post translational modification of anti apoptotic proteins Bcl2 and Bcl-xl in cerebral cortical mitochondria. We propose that phosphorylation of Bcl2 will result in loss of its antiapoptotic potential by preventing its dimerization with Bax leading to activation of the caspase pathway and subsequent neuronal death in the cerebral cortex of the newborn piglets.

Do hyperoxaemia and hypocapnia add to the risk of brain injury after intrapartum asphyxia?

BACKGROUND

Episodes of hyperoxaemia and hypocapnia, which may contribute to brain injury, occur unintentionally in severely asphyxiated neonates in the first postnatal hours.

OBJECTIVE

To determine whether hyperoxaemia and/or hypocapnia during the first 2 hours of life add to the risk of brain injury after intrapartum asphyxia.

METHODS

Retrospective cohort study in term infants with post-asphyxial hypoxic ischaemic encephalopathy (HIE) born between 1985 and 1995. Severe and moderate hyperoxaemia were defined as Pao(2) >26.6 and Pao(2) >13.3 kPa (200 and 100 mm Hg). Severe and moderate hypocapnia were defined as Paco(2) <2.6 and Paco(2) <3.3 kPa (20 and 25 mm Hg). Adverse outcome ascertained by age 24 months was defined as death, severe cerebral palsy, or any cerebral palsy with blindness, deafness, or developmental delay. With outcome as the dependent variable, multivariate analyses were performed including hyperoxaemic and hypocapnic variables, and factors adjusted for initial disease severity.

RESULTS

Of 244 infants, 218 had known outcomes, 127 of which were adverse (64 deaths, 63 neurodevelopmental deficits). Multivariate analyses showed an association between adverse outcome and episodes of severe hyperoxaemia (odds ratio (OR) 3.85, 95% confidence interval (CI) 1.67 to 8.88, p = 0.002), and severe hypocapnia (OR 2.34, 95% CI 1.02 to 5.37, p = 0.044). The risk of adverse outcome was highest in infants who had both severe hyperoxaemia and severe hypocapnia (OR 4.56, 95% CI 1.4 to 14.9, p = 0.012).

CONCLUSIONS

Severe hyperoxaemia and severe hypocapnia were associated with adverse outcome in infants with post-asphyxial HIE. During the first hours of life, oxygen supplementation and ventilation should be rigorously controlled.

Asphyxia aggravates systemic hypotension but not pulmonary hypertension in piglets with meconium aspiration

Meconium aspiration and birth asphyxia are both separately connected to significant pulmonary and systemic hemodynamic changes in newborns, but, although these insults frequently coexist, their combined effects on the neonatal circulation are still controversial. To determine the pulmonary and systemic circulatory changes induced by pulmonary meconium contamination with concurrent asphyxia, 41 anesthetized and ventilated newborn piglets (10-12 d) were studied for 6 h. Eleven piglets were instilled with a bolus of human meconium intratracheally, and 10 piglets had meconium instillation with immediate induction of an asphyxic insult. Eight piglets had only asphyxia and 12 ventilated piglets served as controls. Meconium instillation (with and without asphyxia) resulted in a sustained decrease in the oxygenation, which remained, however, on the control level in the asphyxic group. Although meconium insufflation (with and without asphyxia) increased pulmonary artery pressure and vascular resistance progressively during the study period, the meconium-induced hypertensive effect was actually diminished by additional asphyxia. Asphyxia alone did not have any effect on these pulmonary hemodynamic parameters. On the other hand, whereas systemic arterial pressure and vascular resistance remained on the control level after meconium instillation alone, asphyxia (with and without pulmonary meconium insult) resulted in a sustained fall in systemic pressure already by 4 h. Our data thus indicate that although the coexisting asphyxia seems to moderate the meconium aspiration-induced pulmonary hypertensive response, this additional asphyxic insult does not affect the associated hypoxemia, but rather significantly exacerbates systemic hypotension.

Recent advances in neonatology

This update focuses on recent neonatal research of potential interest to obstetricians. Accurate information on outcomes for infants born at the edges of viability is critical to informing management decisions. New research, population based, gives guidance on short-term survival and long-term neurodevelopmental outcome. Recent research has also highlighted the variation in attitudes to end-of-life decision-making and important influences on this that cross different boundaries. Although research is dominated by issues related to prematurity, some important developments relevant to term infants will be covered. There is accumulating evidence that challenges the traditional approach of using 100% O2 in resuscitation. For infants suffering intrapartum asphyxia there are new approaches to neuroprotection actively being explored. Therapeutic interventions such as extracorporeal membrane oxygenation and inhaled nitric oxide, available for some time, are having their place in neonatal intensive care more clearly defined.