Cerebral excitatory amino acids and Na+,K+-ATPase activity during resuscitation of severely hypoxic newborn piglets

Effect of resuscitation with 21% oxygen and 100% oxygen on NMDA receptor binding characteristics following asphyxia in newborn piglets

The present study investigated the effect of reventilation with 21% and 100% oxygen following asphyxia in newborn piglets on NMDA receptor binding characteristics, Na(+), K(+)-ATPase activity, and lipid peroxidation. After achieving a heart rate less than 60 beats per minute, asphyxiated piglets were reventilated with 21% oxygen or 100% oxygen. (3)[H]MK-801 binding showed the Bmax in the 21% and 100% groups to be 1.53 +/- 0.43 and 1.42 +/- 0.35 pmol/mg protein (p = ns). Values for Kd were 4.56 +/- 1.29 and 4.17 +/- 1.05 nM (p = ns). Na(+), K(+)-ATPase activity in the 21% and 100% groups were 23.5 +/- 0.9 and 24.4 +/- 3.9 micromol Pi/mg protein/h (p = ns). Conjugated dienes (0.05 +/- 0.02 vs. 0.07 +/- 0.03 micromol/g brain) and fluorescent compounds (0.54 +/- 0.05 vs. 0.78 +/- 0.19 microg quinine sulfate/g brain), were similar in both groups (p = ns). Though lipid peroxidation products trended higher in the 100% group, these data show that NMDA receptor binding and Na(+), K(+)-ATPase activity were similar following reventilation with 21% or 100% oxygen after a single episode of mild asphyxia.

Earlier Apgar score increase in severely depressed term infants cared for in Swedish level III units with 40% oxygen versus 100% oxygen resuscitation strategies: a population-based register study

OBJECTIVES

The aim of this study was to evaluate whether a resuscitation strategy based on administration of 40% oxygen influences mortality rates and rates of improvement in 5-minute Apgar scores, compared with a strategy based on 100% oxygen administration.

METHODS

A population-based study evaluated data from 4 Swedish perinatal level III centers during the period of 1998 to 2003. During this period, the centers used either of 2 resuscitation strategies (initial oxygen administration of 40% or 100%). Live-born, singleton, term infants with 1-minute Apgar scores of <4, with a birth weight appropriate for gestational age, and without major malformations were included in the study (n = 1223).

RESULTS

Infants born in hospitals using a 40% oxygen strategy had a more rapid Apgar score increase than did infants born in hospitals using a 100% oxygen strategy; however, no difference remained at 10 minutes. The mean Apgar score increased from 2.01 at 1 minute to 6.74 at 5 minutes in the 2 hospitals initiating resuscitation with 40% oxygen, compared with 2.01 to 6.38 in the 2 hospitals using 100% oxygen, with a mean difference in Apgar score increases of 0.36. At 5 minutes, 44.3% of infants born in the hospitals using 100% oxygen had an Apgar score of <7, compared with 34.0% of infants at the hospitals using 40% oxygen. At 10 minutes, the mean Apgar scores were 8.16 at the hospitals using 40% oxygen and 8.07 at the hospitals using 100% oxygen. There were no significant differences in rates of neonatal death, hypoxic ischemic encephalopathy, or seizures in relation to the 2 oxygen strategies.

CONCLUSION

Severely depressed term infants born in hospitals initiating resuscitation with 40% oxygen had earlier Apgar score recovery than did infants born in hospitals using a 100% oxygen strategy.

Changes of neuronal activity in areas CA1 and CA3 during anoxia and normoxic or hyperoxic reoxygenation in juvenile rat organotypic hippocampal slice cultures

In neonates, asphyxia is usually followed by hyperoxic treatment. In order to study whether hyperoxic reoxygenation might cause additional impairment of neuronal function, we subjected organotypic hippocampal slice cultures of juvenile rats (7 DIV, P6-8) to 30 min anoxia followed by 60 min hyperoxic or normoxic reoxygenation (95% or 19% O2, respectively). Spontaneous and evoked field potentials as well as [Ca2+]o were recorded in the pyramidal layer of area CA1 or area CA3. In area CA1, 30 min of anoxia led to decline of evoked field potential amplitudes by on average 67% and to profound changes in field potential characteristics and Ca2+ homeostasis which were not related to outcome after reoxygenation. Hyperoxic reoxygenation resulted first in a fast recovery of the field potential amplitude to 82% of the control value and then, in 75% of slice cultures, in a large negative field potential shift accompanied by a prolonged decrease of [Ca2+]o and loss of excitability outlasting the experiment. Recovery of field potential amplitude under normoxic conditions stayed poor, with a first increase to 51% and a second decrease to 22%. In contrast, field potential amplitude in area CA3 recovered to 80% of the initial amplitude, irrespective of the reoxygenation mode. The selective loss of function during hyperoxic reoxygenation in area CA1 might be a first sign of neuronal injury that we observed 1 h after end of hyperoxic reoxygenation in a previous study. Whether the poor outcome after normoxic reoxygenation would favour long-term recovery remains to be determined.

Comparison of short- and long-duration oxygen treatment after cerebral asphyxia in newborn piglets

We tested whether reoxygenation with 100% O(2) for 5 min after experimental asphyxia in newborn piglets was as efficient as 100% O(2) for 20 min compared with room air. Forty-one anesthetized piglets, 1-3 d old, were randomized to cerebral hypoxemia-ischemia-hypercapnia (HIH) or control (n = 5). HIH was achieved by ventilation with 8% O(2), temporary occlusion of the common carotid arteries, and adding of CO(2). After 25 min, reoxygenation-reperfusion was started with 100% O(2) for 20 min (group 1, n = 12), 100% O(2) for 5 min (group 2, n = 12), or 21% O(2) (group 3, n = 12). All piglets were observed for 2 h. During reoxygenation-reperfusion, significantly higher blood pressure and more complete restoration of microcirculation (laser Doppler flow) in the cerebral cortex was found in both groups reoxygenated with 100% O(2) compared with 21% O(2) (regional cerebral blood flow >or=100% versus 70% of baseline, p = 0.04). Reoxygenation with 100% O(2) for 5 min was as efficient as 20 min. Oxygen delivery in cortex was significantly higher in groups 1 and 2 compared with group 3 (p = 0.03), but there were no significant differences in cerebral metabolic rate for oxygen. In the striatum, no significant differences in flow or extracellular glutamate, glycerol, and lactate/pyruvate ratio were found between the groups. In conclusion, after experimental asphyxia, newborn piglets can be reoxygenated as efficiently with 100% O(2) for only 5 min as 100% O(2) for 20 min compared with room air.

Cerebral hypoxemia-ischemia and reoxygenation with 21% or 100% oxygen in newborn piglets: effects on extracellular levels of excitatory amino acids and microcirculation

OBJECTIVE

To determine whether reoxygenation with 21% oxygen is preferable to 100% oxygen in normalizing extracellular levels of excitatory amino acids in the brains of hypoxic-ischemic newborn piglets and to compare this model of combined hypoxemia-ischemia to a previously used model of global hypoxemia.

DESIGN

Prospective, randomized animal study.

SETTING

Surgical research laboratory.

SUBJECTS

Twenty-four anesthetized piglets, 1-3 days old.

INTERVENTIONS

Hypoxemia-ischemia was achieved by normoventilation with 8% oxygen and temporary occlusion of the common carotid arteries. After 20 mins, reoxygenation-reperfusion was started with 21% oxygen (HI 21% group, n = 12) or 100% oxygen (HI 100% group, n = 12) for 30 mins followed by 21% oxygen. All piglets were observed for 2 hrs.

MEASUREMENTS AND MAIN RESULTS

We measured extracellular concentrations of amino acids in striatum and hypoxanthine in cerebral cortex (microdialysis), microcirculation in cerebral cortex (laser Doppler), plasma hypoxanthine, and mean arterial pressure. During the 2-hr reoxygenation-reperfusion period, levels of amino acids were significantly higher in the HI 21% group compared with the HI 100% group (glutamate, p = 0.02; aspartate, p = 0.03). Mean arterial pressure was significantly lower in the HI 21% group (p = 0.04). Microcirculation decreased to <10% of baseline during hypoxemia-ischemia and normalized during reoxygenation-reperfusion in the HI 100% group, but it remained at a significantly lower level in the HI 21% group (p = 0.03).

CONCLUSIONS

Significantly higher levels of excitatory amino acids in striatum, significantly lower mean arterial pressure, and a significantly greater degree of hypoperfusion in cerebral cortex were found after reoxygenation with 21% oxygen compared with 100% oxygen in normocapnic, hypoxemic-ischemic newborn piglets. This suggests a less favorable outcome in the group receiving room air.

Resuscitation of newborn infants with room air or oxygen

Oxygen is a toxic agent and a critical approach regarding its use during resuscitation at birth is developing. Animal data indicate that room air is efficient for newborn resuscitation. Three clinical studies have established that normal ventilation is delayed after oxygen resuscitation. Oxidative stress is augmented for several weeks in infants exposed to oxygen at birth -- the long-term implications of these observations remain unclear. There are limited data regarding the use of room air during complicated resuscitations, i.e. in meconium aspiration, the severely asphyxiated infant and in the preterm infant. Thus, it is necessary to continue ongoing rigorous examination of the long-accepted practice of oxygen administration during neonatal resuscitation.