The effect of pretreatment with pentobarbital, meperidine, or hyperbaric oxygen on the response to anoxia and resuscitation in newborn rabbits

Hypoxia - Reoxygenation in neonatal cardiac arrest: Results from experimental models

In this review, we summarize the results of studies that investigated the effects of hypoxia and reoxygenation in cardiac arrest, including the use of different fractions of inspired oxygen, in neonatal animals. The studies were heterogenous in terms of anaesthetic regimens, and definitions of cardiac arrest and circulatory recovery. Cardiopulmonary resuscitation with 100% oxygen increased oxidative stress in maturing rats. Studies in fetal/neonatal lambs and post-transitional neonatal piglets indicate no consistent differences between ventilation with 21% vs. 100% oxygen with regards to recovery times, oxygen damage or adverse events. If 21% oxygen is as effective as 100% oxygen in newborn infants with cardiac arrest requiring chest compression, the use of 21% instead of 100% oxygen could reduce morbidity and mortality in asphyxiated infants. Unanswered questions include what is the most optimal cerebral oxygen delivery during reperfusion, as well as oxygenation targets after return of spontaneous circulation.

Perinatal brain injury: from pathogenesis to neuroprotection

Brain injury secondary to hypoxic-ischemic disease is the predominant form of all brain injury encountered in the perinatal period. The focus of this article is the most recent research developments in this field and especially those developments that should lead to the most profound effects on interventions in the first years of the new millennium. Neuronal injury is the predominant form of cellular injury in the term infant. The principal mechanisms leading to neuronal death after hypoxia-ischemia/reperfusion are initiated by energy depletion, accumulation of extracellular glutamate, and activation of glutamate receptors. The cascade of events that follows involves accumulation of cytosolic calcium and activation of a variety of calcium-mediated deleterious events. Notably this deleterious cascade, which evolves over many hours, may be interrupted even if interventions are instituted after termination of the insult, an important clinical point. Of the potential interventions, the leading candidates for application to the human infant in the relative short-term are mild hypothermia, inhibitors of free radical production, and free radical scavengers. Promising clinical data are available for the use of mild hypothermia.

Effect of pentobarbital on spontaneous recovery from hypoxic apnoea in mice

The effect of pentobarbital anaesthesia on spontaneous recovery from hypoxic apnoea (autoresuscitation) was investigated in SWR/J mice. Experiments were performed in 17 to 23 day old animals, in which the mechanism often fails, and in adults, in which it is usually successful. Mice, matched for age and weight, were injected with pentobarbital (62.5 mg/kg) or saline. Hypoxic apnoea was induced with 97% N2-3% CO2 and air given at its onset. To determine whether the effect of pentobarbital depended on hypothermia, we performed experiments in 17-23-day-olds with and without maintenance of body temperature. In the 'hypothermic' experiments one of 27 mice given pentobarbital died, compared with 10 of 22 controls (P less than 0.005). In the 'isothermic experiments', none of 15 mice given pentobarbital died, compared to 7 of 13 controls (P less than 0.005). All adults in both groups survived. Pentobarbital had a different effect on eupnoea and gasping: resting ventilation was depressed but gasp ventilation increased, and the duty cycle of gasps but not eupnoeic breaths was altered. Pentobarbital may facilitate autoresuscitation because gasping is unimpaired but oxygen consumption and lactate production are reduced, allowing cardiac function and cerebral survival until PO2 is restored.

Thiopentone induced coma after severe birth asphyxia

The aim of this study was to determine the feasibility of inducing a prolonged coma in severely asphyxiated newborn babies by the infusion of high dose thiopentone. In six severely asphyxiated babies the electroencephalograph (EEG) and blood pressure were monitored continuously. Thiopentone was infused at a rate sufficient to suppress completely the EEG providing the mean blood pressure remained above 35 mm Hg; it was continued until there was no evidence of cerebral oedema for 24 hours. In two the infusion was stopped prematurely because of hypotension that was unresponsive to treatment. In the other four a deep coma was maintained for a median duration of 127 hours. All developed pharmacodynamic tolerance to the thiopentone and showed non-linear elimination kinetics. Three babies died; the three survivors have moderate to severe handicap. It was concluded that with full intensive care it is possible to induce a deep coma; the outcome does not seem to be improved, however, and the incidence of complications was high.

Use of barbiturate therapy in severe perinatal asphyxia: a randomized controlled trial

The possible cerebral sparing effect of thiopental was evaluated in 32 severely asphyxiated neonates randomly assigned to either a thiopental treatment or control group. All infants had neurologic manifestations of asphyxia and required assisted ventilation. Thiopental was begun at a mean age of 2.3 hours and was given as a constant infusion that delivered 30 mg/kg over 2 hours. Treatment was continued at a lower dose for 24 hours. Seizure activity occurred in 76% of infants given thiopental and 73% of control infants at a mean age of 1.5 and 2.5 hours, respectively. Although initial arterial blood pressure was similar in both groups, hypotension occurred in 88% of treated and 60% of control infants. The amount of blood pressure support required was significantly greater (P less than 0.005) in the thiopental treatment group. Three infants died in the control group, and five in the treatment group. Developmental assessment was performed at a minimum of 12 months of age in 22 infants. There were no significant differences in neurologic, cognitive, or motor outcome between groups. Deteriorating performance over time was a consistent trend in both groups. These findings indicate that treatment of severe perinatal asphyxia with thiopental does not appear to have a cerebral sparing effect and may be associated with significant arterial hypotension.

Disaggregation of polyribosomes in intact gerbils following ischemia. An ultrastructural study

Adult gerbils were subjected to either unilateral or bilateral common carotid artery ligation for varying periods of time with varying durations of recovery. Selected brain regions were prepared for ultrastructural study after perfusion fixation. Dissociation of polyribosomes was observed in neurons but not in glial cells of the cerebral cortex and thalamus after 30 minutes of unilateral occlusion with no recovery period. At the other extreme, disaggregation was present in all brain regions studied after 60 minutes of bilateral occlusion followed by a 60-minute recovery period. Still longer recovery periods result in the appearance of some neurons with normally aggregated polyribosomes. The results suggest that a relatively long period of ischemia induces a derangement of neuronal protein synthesis that may persist for some time after restoration of circulation.