Resuscitation with 100% oxygen causes intestinal glutathione oxidation and reoxygenation injury in asphyxiated newborn piglets

Gene expression in the intestine of newborn piglets after hypoxia-reoxygenation

BACKGROUND

In preterm infants, intestinal hypoxia may partly contribute to the pathophysiology of necrotizing enterocolitis through changes in gene expression. Splanchnic hypoxia can be detected with monitoring of regional splanchnic oxygen saturation (rsSO2). Using a piglet model of asphyxia, we aimed to correlate changes in rsSO2 to gene expression.

METHODS

Forty-two newborn piglets were randomized to control or intervention groups. Intervention groups were subjected to hypoxia until they were acidotic and hypotensive. Next, they were reoxygenated for 30 min according to randomization, i.e., 21% O2, 100% O2, or 100% O2 for 3 min followed by 21% O2, and observed for 9 h. We continuously measured rsSO2 and calculated mean rsSO2 and variability of rsSO2 (rsCoVar = SD/mean). Samples of terminal ileum were analyzed for mRNA expression of selected genes related to inflammation, erythropoiesis, fatty acid metabolism, and apoptosis.

RESULTS

The expression of selected genes was not significantly different between control and intervention groups. No associations between mean rsSO2 and gene expression were observed. However, lower rsCoVar was associated with the upregulation of apoptotic genes and the downregulation of inflammatory genes (P < 0.05).

CONCLUSION

Our study suggests that hypoxia and reoxygenation cause reduced vascular adaptability, which seems to be associated with the upregulation of apoptosis and downregulation of inflammation.

IMPACT

Our results provide important insight into the (patho)physiological significance of changes in the variability of rsSO2. Our findings may advance future research and clinical practice regarding resuscitation strategies of preterm infants.

Cardiovascular Supportive Therapies for Neonates With Asphyxia - A Literature Review of Pre-clinical and Clinical Studies

Asphyxiated neonates often have hypotension, shock, and poor tissue perfusion. Various "inotropic" medications are used to provide cardiovascular support to improve the blood pressure and to treat shock. However, there is incomplete literature on the examination of hemodynamic effects of these medications in asphyxiated neonates, especially in the realm of clinical studies (mostly in late preterm or term populations). Although the extrapolation of findings from animal studies and other clinical populations such as children and adults require caution, it seems appropriate that findings from carefully conducted pre-clinical studies are important in answering some of the fundamental knowledge gaps. Based on a literature search, this review discusses the current available information, from both clinical studies and animal models of neonatal asphyxia, on common medications used to provide hemodynamic support including dopamine, dobutamine, epinephrine, milrinone, norepinephrine, vasopressin, levosimendan, and hydrocortisone.

Pentoxifylline therapy attenuates intestinal injury in rat pups with hypoxic ischemic encephalopathy

AIM

The aim of this study was to evaluate the effects of post-ischemic pentoxifylline (PTX) therapy on the gut injury in neonatal rat model of hypoxic ischemic encephalopathy (HIE).

METHODS

Seven-day-old Wistar rat pups (n = 24) of either sex, delivered spontaneously, were used in this experimental study. Seven-day-old rat pups were randomly divided into three groups. Control group (n = 8): after median neck incision was made, neither ligation nor hypoxia was performed. Hypoxia group (n = 8): 0.5 ml of saline was injected intraperitoneally immediately after hypoxia. Pentoxifylline + Hypoxia group (n = 8): the rat pups were administered intraperitoneally 60 mg/kg of PTX immediately after hypoxia. Eight rats from all groups were sacrificed 24 h after drug administration. The ischemic injury was scored at least six sections at three different levels using histopathologic injury scores (HIS).

RESULTS

Induction of hypoxia/reoxygenation (H/R) increased mean HIS levels significantly at 24 h in the intestinal tissue samples in the hypoxia group as compared with the control group. Induction of H/R decreased means HIS levels significantly at 24 h in the intestinal tissue samples in the PTX + hypoxia group as compared with the hypoxia group.

CONCLUSION

In this experimental study, PTX significantly attenuated H/R-induced intestinal injury in neonatal rat model of HIE. These findings indicate that PTX can reduce the intestinal H/R injury.

Cardiopulmonary resuscitation with chest compressions during sustained inflations: a new technique of neonatal resuscitation that improves recovery and survival in a neonatal porcine model

BACKGROUND

Guidelines on neonatal resuscitation recommend 90 chest compressions (CCs) and 30 manual inflations (3:1) per minute in newborns. The study aimed to determine whether CC s during sustained inflations (SIs) improves the recovery of asphyxiated newborn piglets in comparison with coordinated 3:1 resuscitation.

METHODS AND RESULTS

Term newborn piglets (n=8/group) were anesthetized, intubated, instrumented, and exposed to 45-minute normocapnic hypoxia followed by asphyxia. Piglets were randomly assigned to receive either 3:1 resuscitation (3:1 group) or CCs during SIs (SI group) when the heart rate decreased to 25% of baseline. Piglets randomly assigned to the SI group received SIs with a pressure of 30 cm H2O for 30 s. During the SI, CCs at a rate of 120/min were provided. SI was interrupted after 30 s for 1 s before a further 30-s SI was provided. CCs were continued throughout SIs. CCs and SI were continued until the return of spontaneous circulation. Continuous respiratory parameters, cardiac output, mean systemic and pulmonary artery pressures, and regional blood flows were measured. Mean (standard deviation) time for return of spontaneous circulation was significantly reduced in SI group versus 3:1 group (32 [11] s versus 205 [113] s, respectively). In the SI group, administration of oxygen and epinephrine was significantly lower, whereas minute ventilation and exhaled CO2 were significantly increased. The SI group had significantly higher mean systemic and pulmonary arterial pressures during resuscitation in comparison with the 3:1 group (51 [10] versus 31 [5] mm Hg; 41[7] versus 31 [7] mm Hg, respectively; all P<0.05), with improved cardiac output and carotid blood flow.

CONCLUSIONS

Combining CCs and SIs significantly improved the return of spontaneous circulation with better hemodynamic recovery in asphyxiated newborn piglets in comparison with standard coordinated 3:1 resuscitation.

The role of oxygen in the delivery room

As recently as the year 2000, 100% oxygen was recommended to begin resuscitation of depressed newborns in the delivery room. However, the most recent recommendations of the International Liaison Committee on Resuscitation counsel the prudent use of oxygen during resuscitation. In term and preterm infants, oxygen therapy should be guided by pulse oximetry that follows the interquartile range of preductal saturations of healthy term babies after vaginal birth at sea level. This article reviews the literature in this context, which supports the radical but judicious curtailment of the use of oxygen in resuscitation at birth.

Hypoxic-ischemic injury in the developing brain: the role of reactive oxygen species originating in mitochondria

Mitochondrial dysfunction is the most fundamental mechanism of cell damage in cerebral hypoxia-ischemia and reperfusion. Mitochondrial respiratory chain (MRC) is increasingly recognized as a source for reactive oxygen species (ROS) in the postischemic tissue. Potentially, ROS originating in MRC can contribute to the reperfusion-driven oxidative stress, promoting mitochondrial membrane permeabilization. The loss of mitochondrial membranes integrity during reperfusion is considered as the major mechanism of secondary energy failure. This paper focuses on current data that support a pathogenic role of ROS originating from mitochondrial respiratory chain in the promotion of secondary energy failure and proposes potential therapeutic strategy against reperfusion-driven oxidative stress following hypoxia-ischemia-reperfusion injury of the developing brain.

Cyclosporine treatment improves mesenteric perfusion and attenuates necrotizing enterocolitis (NEC)-like intestinal injury in asphyxiated newborn piglets during reoxygenation

PURPOSE

Asphyxia-related intestinal injury in neonates may present similar to necrotizing enterocolitis (NEC) and is partially associated with hypoxia-reoxygenation injury. Cyclosporine has been shown to reduce myocardial cell death following ischemia-reperfusion. We hypothesize that cyclosporine treatment may attenuate NEC-like intestinal injury in asphyxiated newborn piglets during reoxygenation.

METHODS

Twenty piglets (1-4 days old) were acutely anesthetized and instrumented for continuous monitoring of systemic hemodynamics and superior mesenteric arterial (SMA) flow. After stabilization, normocapnic alveolar hypoxia (10-15% oxygen) was instituted for 2 h followed by reoxygenation with 100% oxygen for 0.5 h, then 21% for 3.5 h. The piglets were blindly block-randomized to receive cyclosporine (10 mg/kg) or placebo (normal saline) boluses at 5 min of reoxygenation (n = 8/group). A sham-operated group was included (n = 4) and received no hypoxia-reoxygenation. Intestinal samples were collected for tissue lactate and histological assessment (Park's criteria).

RESULTS

At 2 h of hypoxia, piglets had cardiogenic shock (cardiac output 45% of baseline), hypotension (mean arterial pressure 30 mmHg), acidosis (pH 7.04), and decreased superior mesenteric perfusion (all P < 0.05 vs. sham-operated group, ANOVA). Cyclosporine treatment increased SMA flow (114 ± 6 vs. 78 ± 19% of baseline of controls, respectively) with improved SMA oxygen delivery and intestinal tissue lactate (all P < 0.05). Some control piglets had NEC-like injuries including pneumatosis intestinalis, which were attenuated in cyclosporine-treated piglets (P < 0.05 vs. controls).

CONCLUSIONS

This is the first study to demonstrate that post-resuscitation administration of cyclosporine improves mesenteric perfusion and attenuates NEC-like intestinal injury in newborn piglets following asphyxia-reoxygenation.

Vasopressin improves systemic hemodynamics without compromising mesenteric perfusion in the resuscitation of asphyxiated newborn piglets: a dose-response study

PURPOSE

Hypoxia and reoxygenation (H-R) contributes to multi-organ failure in neonates, including cardiac and systemic complications. Use of vasopressin, an endogenous vasoconstrictive hormone commonly used to treat refractory hypotension in adults, in neonates with shock remains limited and not yet fully studied. We hypothesize that vasopressin will improve mean arterial pressure (MAP), without compromising cardiac, mesenteric, or carotid hemodynamics using a swine model of neonatal asphyxia.

METHODS

Anesthetized piglets (1-4 days old, 1.4-2.5 kg, n = 33) were instrumented for continuous monitoring of cardiac index (CI), MAP, and regional arterial [common carotid (CA), superior mesenteric (SMA)] flow. The animals underwent hypoxia at 10-15% oxygen (2 h) followed by reoxygenation at 100% (0.5 h) and 21% (3.5 h) oxygen. Vasopressin infusion was initiated after 2 h reoxygenation at 0.005, 0.01, or 0.02 units/kg/h i.v. for 2 h (n = 7/group). H-R control (saline infusion) and sham-operated (non-asphyxiated) groups were also included. Intermittent blood gases and plasma lactate were determined as well as tissue lactate levels. Statistical significance was determined using ANOVA.

RESULTS

All H-R piglets had hypotension (36-49% decrease in MAP) and decreased regional blood flows (CA -28 to -34%, SMA -12 to +32% of baseline) at 2 h reoxygenation. Vasopressin infusion dose-dependently increased MAP (14% at 0.02 units/kg/h, P < 0.05) without significant detrimental effects in CI, regional blood flows, and intestinal or cerebral tissue lactate levels.

CONCLUSIONS

Vasopressin treatment causes a dose-dependent baro-specific effect, while preserving cardiac function and cerebral and mesenteric hemodynamics in newborn piglets following H-R.

A swine model of neonatal asphyxia

Annually more than 1 million neonates die worldwide as related to asphyxia. Asphyxiated neonates commonly have multi-organ failure including hypotension, perfusion deficit, hypoxic-ischemic encephalopathy, pulmonary hypertension, vasculopathic enterocolitis, renal failure and thrombo-embolic complications. Animal models are developed to help us understand the patho-physiology and pharmacology of neonatal asphyxia. In comparison to rodents and newborn lambs, the newborn piglet has been proven to be a valuable model. The newborn piglet has several advantages including similar development as that of 36-38 weeks human fetus with comparable body systems, large body size (~1.5-2 kg at birth) that allows the instrumentation and monitoring of the animal and controls the confounding variables of hypoxia and hemodynamic derangements. We here describe an experimental protocol to simulate neonatal asphyxia and allow us to examine the systemic and regional hemodynamic changes during the asphyxiating and reoxygenation process as well as the respective effects of interventions. Further, the model has the advantage of studying multi-organ failure or dysfunction simultaneously and the interaction with various body systems. The experimental model is a non-survival procedure that involves the surgical instrumentation of newborn piglets (1-3 day-old and 1.5-2.5 kg weight, mixed breed) to allow the establishment of mechanical ventilation, vascular (arterial and central venous) access and the placement of catheters and flow probes (Transonic Inc.) for the continuously monitoring of intra-vascular pressure and blood flow across different arteries including main pulmonary, common carotid, superior mesenteric and left renal arteries. Using these surgically instrumented piglets, after stabilization for 30-60 minutes as defined by Z<10% variation in hemodynamic parameters and normal blood gases, we commence an experimental protocol of severe hypoxemia which is induced via normocapnic alveolar hypoxia. The piglet is ventilated with 10-15% oxygen by increasing the inhaled concentration of nitrogen gas for 2h, aiming for arterial oxygen saturations of 30-40%. This degree of hypoxemia will produce clinical asphyxia with severe metabolic acidosis, systemic hypotension and cardiogenic shock with hypoperfusion to vital organs. The hypoxia is followed by reoxygenation with 100% oxygen for 0.5 h and then 21% oxygen for 3.5 h. Pharmacologic interventions can be introduced in due course and their effects investigated in a blinded, block-randomized fashion.

Intestinal gene expression in pigs: effects of reduced feed intake during weaning and potential impact of dietary components

The weaning transition is characterised by morphological, histological and microbial changes, often leading to weaning-associated disorders. These intestinal changes can partly be ascribed to the lack of luminal nutrition arising from the reduced feed intake common in pigs after weaning. It is increasingly becoming clear that changes in the supply with enteral nutrients may have major impacts on intestinal gene expression. Furthermore, the major dietary constituents, i.e. carbohydrates, fatty acids and amino acids, participate in the regulation of intestinal gene expression. However, nutrients may also escape digestion by mammalian enzymes in the upper gastrointestinal tract. These nutrients can be used by the microflora, resulting in the production of bacterial metabolites, for example, SCFA, which may affect intestinal gene expression indirectly. The present review provides an insight on possible effects of reduced feed intake on intestinal gene expression, as it may occur post-weaning. Detailed knowledge on effects of reduced feed intake on intestinal gene expression may help to understand weaning-associated intestinal dysfunctions and diseases. Examples are given of intestinal genes which may be altered in their expression due to supply with specific nutrients. In that way, gene expression could be modulated by dietary means, thereby acting as a potential therapeutic tool. This could be achieved, for example, by influencing genes coding for digestive or absorptive proteins, thus optimising digestive function and metabolism, but also with regard to immune response, or by influencing proliferative processes, thereby enhancing mucosal repair. This would be of special interest when designing a diet to overcome weaning-associated problems.

Plasma cortisol response to ACTH challenge in hypoxic newborn piglets resuscitated with 21% and 100% oxygen

Although the use of supplemental oxygen to resuscitate asphyxiated neonates remains controversial, the effects of hypoxia and reoxygenation (room air versus pure oxygen) on the hypothalamo-pituitary-adrenal axis are unknown. We aimed to evaluate the effect of hypoxia and reoxygenation with either 21% or 100% oxygen on plasma cortisol before and after an adrenocorticotrophin (ACTH) challenge in newborn piglets. Thirty-five piglets (aged 1-3 days, weighing 1.5-2.4 kg) were instrumented to measure heart rate, MAP, and cardiac output. After 2 h of normocapnic hypoxia (PaO2, 20-30 mmHg; pH, <6.95), piglets were resuscitated with 21% or 100% oxygen for 1 h and then 21% oxygen for 3 h. Sham-operated piglets had no hypoxia-reoxygenation (H-R). Serial plasma cortisol levels were determined after a blinded randomized administration of ACTH (4 microg/kg, i.v.) or saline at 2 h reoxygenation. The expression of steroidogenic factor 1 in the adrenals was studied. Cardiac output decreased with hypoxia and recovered with resuscitation. Piglets developed hypotension similarly in 21% and 100% H-R groups during reoxygenation (versus sham-operated group, P < 0.05). Both H-R groups had increased plasma cortisol levels (versus sham-operated group, P < 0.05) at 2 h of reoxygenation after hypoxia, with a further increase in levels in 21% H-R piglets at 4 h reoxygenation (versus 100% H-R piglets, P < 0.05). The response to ACTH was delayed in H-R groups, with the maximum increase at 120 min post-ACTH administration (versus 30-60 min post-ACTH for sham-operated piglets). Plasma cortisol levels increased significantly post-ACTH administration in 21% H-R and sham-operated piglets (115% +/-50% and 126% +/- 25% at 120 min, respectively, P < 0.05 vs. pre-ACTH baselines) but not in 100% H-R piglets (51% +/-14%), which had a lower expression of steroidogenic factor 1 than the other groups. Although the clinical significance of high cortisol levels and cortisol response to ACTH in H-R newborn piglets is uncertain, a preserved cortisol response may support using room air in neonatal resuscitation.

The antioxidant role of oral administration of garlic oil on renal ischemia-reperfusion injury

AIM

In this study we examined the effect of oral application of garlic form [garlic oil (GO)] on rats after renal ischemia-reperfusion (I/R) injury.

MATERIALS AND METHODS

Forty male Wistar albino rats were divided into four groups: control, sham-operated, I/R, and I/R+GO. GO was diluted in water and administered by oral intubation three times each week for 6 weeks. All rats except sham-operated underwent 45 min of bilateral renal ischemia followed by 6 hr of reperfusion. Blood samples and kidney tissues were harvested from the rats, and then rats were killed. Serum urea, creatinine, and cystatin C levels were determined. Total antioxidant capacity (TAC), catalase (CAT), total oxidant status (TOS), oxidative stress index (OSI), myeloperoxidase (MPO), nitrite oxide (NO), and protein carbonyl (PC) levels in kidney tissue and blood were measured. In addition, kidney tissue histopathology was evaluated.

RESULTS

The serum urea, creatinine, and cystatin C levels were significantly higher in I/R group compared to I/R+GO group (p<0.01). The serum and tissue antioxidant markers (TAC, CAT) were significantly lower in I/R group than I/R+GO group (p<0.01). The serum oxidant markers (TOS, MPO, NO, and PC) were significantly higher in I/R group than I/R+GO group (p<0.01). Also oral application of GO was effective in decreasing of tubular necrosis score.

CONCLUSION

Based on the present data, we conclude that increased antioxidants and decreased oxidants modulated by oral application of GO attenuated the renal I/R injury.

Angiostatins decrease in the kidney of newborn piglets after hypoxia-reoxygenation

Little is known about the expression of kidney angiostatin in the hypoxia and reoxygenation of neonates. In this study, we compared the effect of 21% and 100% reoxygenation on kidney levels of angiostatin and its related factors in newborn piglets subjected to hypoxia-reoxygenation. Newborn piglets were subjected to 2h hypoxia followed by 1h of reoxygenation with either 21% or 100% oxygen and observed for 4days. There were 3 isoforms (38, 43 and 50kDa) of angiostatins identified in the kidney tissue of newborn piglets with the 38kDa being the major isoform (~60%). The 38kDa, but not 43 and 50kDa, angiostatin isoform correlated significantly with the levels of total angiostatin and plasminogen (r=0.95 and r=0.58, respectively). On day 4 of recovery in 100% hypoxic-reoxygenated group, there were decreases in kidney tissue levels of plasminogen, total angiostatin, angiostatin (38 and 43kDa, but not 50kDa), whereas no significant changes were found in the 21% hypoxic-reoxygenated group when compared to the sham-operated piglets with no hypoxia-reoxygenation. Both 21% and 100% hypoxic-reoxygenated groups did not show significant changes in kidney tissue levels of 50kDa angiostatin, MMP-2, MMP-9 and HIF-1alpha. In comparison to 21% oxygen, neonatal resuscitation with 100% oxygen decreased the kidney tissue levels of plasminogen and angiostatin that may play a role in neonatal kidney injury and altered renal development in adulthood.

Protective effects of Nigella sativa against ischemia-reperfusion injury of kidneys

BACKGROUND

Ischemia-reperfusion, commonly seen in the fields of trauma surgery and renal transplantation, is a major cause of acute kidney injury and is associated with significant morbidity and mortality. The protective effects of Nigella sativa against ischemia-perfusion damage to various organs have been previously documented. However, its protective effects on kidney tissue against ischemia-reperfusion injury are unclear. In this study, we aimed to examine the effect of Nigella sativa in modulating inflammation and apoptosis after renal I/R injury.

MATERIALS AND METHODS

Thirty male Wistar-albino rats were divided into three groups: sham-operated, ischemia-reperfusion, and ischemia-reperfusion + Nigella sativa. Rats in the third group were given Nigella sativa 6 h prior to ischemia-reperfusion and at the beginning of reperfusion. All rats except those in the sham-operated group underwent 45 min of bilateral renal ischemia followed by 45 min of reperfusion. Blood samples and liver tissues were harvested from the rats, and then rats were sacrificed. Serum urea and creatinine levels were determined. Total antioxidant capacity (TAC), catalase (CAT), total oxidant status (TOS), oxidative stress index (OSI), and myeloperoxidase (MPO) in kidney tissue and blood were measured. Kidney tissue histopathology was also evaluated. Results. Nigella sativa was effective in reducing serum urea and creatinine levels as well as decreasing the tubular necrosis score. Nigella sativa treatment significantly reduced OSI and TOS levels and increased TAC levels in both kidney tissue and blood.

CONCLUSION

The observed differences seem to demonstrate the protective effect of Nigella sativa against renal I/R injury in rat kidneys.

The state of systemic circulation, collapsed or preserved defines the need for hyperoxic or normoxic resuscitation in neonatal mice with hypoxia-ischemia

BACKGROUND

The return of spontaneous circulation (ROSC) is a primary goal of resuscitation. For neonatal resuscitation the International Liaison Committee on Resuscitation (ILCOR) recommends oxygen concentrations ranging from 21% to 100%.

AIMS AND METHODS

This study (a) compared the efficacy of resuscitation with room air (RA) or 100% O(2) in achieving ROSC in 46 neonatal mice with circulatory collapse induced by lethal hypoxia-ischemia (HI) and (b) determined whether re-oxygenation with RA or 100% O(2) alters the extent of HI cerebral injury in mice with preserved systemic circulation (n=31). We also compared changes in generation of reactive oxygen species (ROS) in cerebral mitochondria in response to re-oxygenation with RA or 100% O(2).

RESULT

In HI-mice with collapsed circulation re-oxygenation with 100% O(2) versus RA resulted in significantly greater rate of ROSC. In HI-mice with preserved systemic circulation and regional (unilateral) cerebral ischemia the restoration of cerebral blood flow was significantly faster upon re-oxygenation with 100% O(2), than RA. However, no difference in the extent of brain injury was detected. Regardless of the mode of re-oxygenation, reperfusion in these mice was associated with markedly accelerated ROS production in brain mitochondria.

CONCLUSION

In murine HI associated with circulatory collapse the resuscitation limited to re-oxygenation with 100% O(2) is superior to the use of RA in achievement of the ROSC. However, in HI-mice with preserved systemic circulation hyperoxic re-oxygenation has no benefit over the normoxic brain recovery.

Cardiac dysfunction in an animal model of neonatal asphyxia is associated with increased degradation of MLC1 by MMP-2

The purpose of this study was to determine if decreased heart function after hypoxia followed by reoxygenation (H-R) is associated with increased degradation of cardiac myosin light chain 1 (MLC1) by matrix metalloproteinase-2 (MMP-2), and to investigate the effects of the increased level of peroxynitrite in the hearts of H-R animals on MLC1 degradation by MMP-2. Total of 12 newborn piglets were acutely instrumented to monitor cardiac function as assessed by stroke volume. Anesthetized piglets were block randomized to the normoxic group (n = 6), which received ventilation with room air for 6 h, or to the H-R group (n = 6), which received ventilation with 10-15% oxygen for 2 h, followed by reoxygenation with 100% oxygen for 1 h and then with 21% oxygen for 3 h. Hearts were removed and snap frozen for subsequent biochemical analyses. At the end of the 2-h hypoxia period, cardiac output, mean arterial pressure and stroke volume were significantly decreased in the H-R group. After 1 h of 100% oxygen, these parameters had increased slightly, but remained significantly lower than the normoxic controls throughout the reoxygenation period. Compared to normoxic animals, cardiac MLC1 levels were decreased and MMP-2 activity was increased in H-R animals. MMP-2 was co-localized with MLC1, and the amount of MLC1 associated with MMP-2 was higher in the hearts of H-R animals. In normoxic animals, cardiac MLC1 level was negatively, and cardiac MMP-2 activity was positively, strongly correlated with stroke volume index. This relationship was not seen in the H-R group. However, in both the normoxic group and the H-R group, the activity of cardiac MMP-2 was negatively correlated with the level of cardiac MLC1. There was a more than twofold increase in the level of nitrates, a marker for peroxynitrite formation, in the hearts of H-R animals. Mass spectrometric analyses detected peroxynitrite-induced nitration and S-nitrosylation of MLC1 protein in the hearts of H-R animals. These peroxynitrite-induced modifications of MLC1 were localized directly adjacent to the site at which MMP-2 cleaves MLC1. Peroxynitrite, formed during cardiac reoxygenation following a period of hypoxia, modifies the structure of cardiac MLC1 by nitrating and nitrosylating amino acids adjacent to the site where MMP-2 cleaves MLC1. This facilitates the degradation of MLC1 by MMP-2 and may contribute to cardiac dysfunction induced by H-R and other forms of oxidative stress. The high correlation between MMP-2 activity and MLC1 level in control animals suggests that MMP-2 may play an important role in regulating MLC1 turnover under normal physiological conditions. Determining the optimal parameters for controlled reoxygenation after hypoxia, together with pharmacological treatment with MMP-2 inhibitors and/or inhibitors of nitration/nitrosylation of MLC1, could reduce heart injury during the resuscitation of asphyxiated newborns and improve their long-term prognosis by reducing MLC1 degradation. Since the degradation of MLC1 by MMP-2 appears to be a common feature of oxidative stress, these pharmacological interventions may be useful in reducing tissue damage in other oxidative stress-related disorders as well.

Room air or 100% oxygen for resuscitation of infants with perinatal depression

PURPOSE OF REVIEW

The International Liaison Committee on Resuscitation (ILCOR) recommends initiating neonatal resuscitation with concentrations of oxygen between 21 and 100%. This wide range of oxygen concentrations recommended for resuscitation highlights the lack of evidence supporting either 21 or 100% O2. The purpose of this review is to analyze the efficacy of reoxygenation with 100% O2 or room air on rates of return of spontaneous circulation--the main goal of cardiopulmonary resuscitation.

RECENT FINDINGS

Clinical studies suggest that reoxygenation initiated with room air is effective in depressed neonates born with a preserved circulation. Reoxygenation with room air in these infants is associated with lower levels of circulating markers of oxidative stress than reoxygenation with 100% oxygen. However, there is no evidence that resuscitation with room air is as effective as that with 100% oxygen in restoration of an arrested circulation. In fact, animal studies indicate that, in comparison with 100% oxygen, reoxygenation with room air results in more sluggish restoration of depressed cerebral and systemic circulations.

SUMMARY

Prior to a revision of current neonatal resuscitation guidelines it must be determined whether resuscitation initiated with room air results in the same rate of return of spontaneous circulation as resuscitation initiated with 100% oxygen.

Epinephrine versus dopamine to treat shock in hypoxic newborn pigs resuscitated with 100% oxygen

Shock and tissue hypoperfusion are common after asphyxia. We compared systemic and regional hemodynamic effects of epinephrine and dopamine in the treatment of shock and hypotension in asphyxiated newborn piglets resuscitated with 100% oxygen. Twenty-four piglets (1-3 days old; weight, 1.4-2.6 kg) were acutely instrumented to measure cardiac index (CI), carotid, mesenteric and renal arterial blood flows, and mean systemic (SAPs) and pulmonary arterial pressures (PAPs). Piglets had normocapnic alveolar hypoxia (F(IO2)=0.08-0.10) for 50 min and reoxygenated with F(IO2)=1.0 for 1 h then F(IO2)=0.21 for 3.5 h. After 2 h reoxygenation, either dopamine (2 microg kg(-1) min(-1)) or epinephrine (0.2 microg kg(-1) min(-1)) was given for 30 min in a blinded randomized manner, which was then increased to maintain SAP (within 10% of baseline, pressure-driven dose) for 2 h. Hypoxia caused hypotension (SAP, 44%+/-3% of baseline), cardiogenic shock (CI, 41%+/-4%), and metabolic acidosis (mean pH, 7.04-7.09). Upon reoxygenation, hemodynamic parameters immediately recovered but gradually deteriorated during 2 h with SAP at 45+/-1 mmHg, CI at 74+/-9% of baseline, and pH 7.32+/-0.03. Low doses of either drug had no significant systemic and renal hemodynamic response. Epinephrine (0.3-1.5 microg kg(-1) min(-1)) for 2 h increased SAP and CI (with higher stroke volume) and decreased pulmonary vascular resistance (with reduced PAP-SAP ratio), whereas the responses with dopamine (10-25 microg kg(-1) min(-1)) were modest. Low-dose epinephrine improved mesenteric and carotid arterial flows, whereas the pressure-driven doses of epinephrine and dopamine increased carotid and mesenteric arterial flows, respectively. To treat shock in asphyxiated newborn piglets resuscitated with 100% oxygen, epinephrine exhibits an inotropic action compared with dopamine, whereas both catecholamines can increase carotid and mesenteric perfusion.

N-acetylcysteine improves the hemodynamics and oxidative stress in hypoxic newborn pigs reoxygenated with 100% oxygen

Neonatal asphyxia may lead to cardiac and renal complications perhaps mediated by oxygen free radicals. Using a model of neonatal hypoxia-reoxygenation, we tested the hypothesis that N-acetylcysteine (NAC) would improve cardiac function and renal blood flow. Eighteen piglets (aged 1-4 days old, weighing 1.4-2.2 kg) were anesthetized and acutely instrumented for continuous monitoring of pulmonary and renal artery flow (cardiac index [CI] and renal artery flow index [RAFI], respectively) and mean blood pressure. Alveolar hypoxia was induced for 2 h, followed by resuscitation with 100% oxygen for 1 h and 21% oxygen for 3 h. Animals were randomized to sham-operated, hypoxic control, and NAC treatment (i.v. bolus of 150 mg/kg given at 10 min of reoxygenation followed by 100 mg/kg per h infusion) groups. Myocardial and renal tissue glutathione content and lipid hydroperoxide levels were assayed, and histology was examined. After 2 h of hypoxia, all animals were acidotic (pH 6.96 +/- 0.04) and in cardiogenic shock with depressed renal blood flow. Upon reoxygenation, CI and RAFI increased but gradually deteriorated later. The NAC treatment prevented the decreased CI, stroke volume, mean blood pressure, systemic oxygen delivery, RAFI, and renal oxygen delivery at 2 to 4 h of reoxygenation observed in hypoxic controls (versus shams, all P < 0.05). The myocardial and renal tissue glutathione content was significantly higher in the NAC treatment group (versus controls). The CI and RAFI at 4 h of reoxygenation correlated with the tissue glutathione redox ratio (r = 0.5 and 0.6, respectively, P < 0.05). There were no significant differences in heart rate, pulmonary artery pressure, systemic oxygen uptake, and tissue lipid hydroperoxide levels between groups. No histologic injury was found in the heart or kidney. In this porcine model of neonatal hypoxia and 100% reoxygenation, NAC improved cardiac function and renal perfusion, with improved tissue glutathione content.

Oxidative stress and matrix metalloproteinase-9 activity in the liver after hypoxia and reoxygenation with 21% or 100% oxygen in newborn piglets

We designed a randomized controlled study to identify and compare the liver tissue responses in systemic hypoxia and resuscitation with 21% and 100% oxygen using an animal model of neonatal hypoxia and reoxygenation. Twenty-seven piglets (1-3 days old, weight 1.5-2.0 kg) were acutely instrumented and mechanically ventilated. The animals underwent 2 h of normocapnic alveolar hypoxia (10-15% oxygen) then reoxygenation with 21% or 100% oxygen for 1 h, then 1 h with 21% oxygen. Controls were sham-operated without hypoxia-reoxygenation. After 2 h of reoxygenation liver tissue samples were immediately processed for histological and biochemical analyses of markers of oxidative stress and tissue injury. Two hours of hypoxia caused a significant reduction in mean arterial pressure with cardiogenic shock and metabolic acidemia, with similar recovery upon resuscitation with 21% and 100% oxygen. After 2 h of reoxygenation, the hepatic GSSG:total glutathione ratio and matrix metalloproteninase-9 activity, which correlated with the portal venous oxygenation at 15 min of reoxygenation, were greater in the 100% group and hepatic lactate level was higher in the 21% group than the controls (all P<0.05). Both hypoxic-reoxygenated groups had similarly elevated hepatic Bcl-2 levels. Apart from more non-distinct mitochondria identified in the 100% group, hepatic tissue adenylate energy charge and plasma transaminases levels did not differ among groups. We concluded that in this acute model of neonatal hypoxia and reoxygenation, resuscitation using 21% oxygen avoids the excess oxidative stress and elevated matrix metalloproteninase-9 activity in the liver when 100% oxygen was used. The study supports the conservative use of oxygen in optimizing post-hypoxic hepatic recovery.

Postresuscitation N-acetylcysteine treatment reduces cerebral hydrogen peroxide in the hypoxic piglet brain

OBJECTIVE

Reactive oxygen species have been implicated in the pathogenesis of hypoxia-reoxygenation injury. However, little information is known regarding the temporal profile of cerebral hydrogen peroxide (HPO) production and its response to N-acetylcysteine (an antioxidant) administration during neonatal hypoxia-reoxygenation. Using an acute swine model of neonatal hypoxia-reoxygenation, we examined the short-term neuroprotective effects of N-acetylcysteine on cerebral HPO production and oxidative stress in the brain.

DESIGN

Controlled, block-randomized animal study.

SETTING

University animal research laboratory.

SUBJECTS

Newborn piglets (1-3 days, 1.7-2.1 kg).

INTERVENTIONS

At 5 min after reoxygenation, piglets were given either saline or N-acetylcysteine (20 or 100 mg/kg/h) in a blinded, randomized fashion.

MEASUREMENTS AND RESULTS

Newborn piglets were block-randomized into a sham-operated group (without hypoxia-reoxygenation, n = 5) and three hypoxic-reoxygenated groups (2 h of normocapnic alveolar hypoxia followed by 2h of reoxygenation, n = 7/group). Heart rate, mean arterial pressure, cortical HPO concentration, amino acid levels in cerebral microdialysate, and cerebral tissue glutathione and lipid hydroperoxide levels were examined. Hypoxic piglets were hypotensive and acidotic, and they recovered similarly in all hypoxic-reoxygenated groups. In hypoxic-reoxygenated control piglets, the cortical HPO concentration gradually increased during reoxygenation. Both doses of N-acetylcysteine abolished the increased HPO concentration and oxidized glutathione levels and tended to reduce the glutathione ratio and lipid hydroperoxide levels in the cerebral cortex (p = 0.08 and p = 0.1 vs. controls, respectively). N-acetylcysteine at 100mg/kg/h also increased the cerebral extracellular taurine levels.

CONCLUSION

In newborn piglets with hypoxia-reoxygenation, postresuscitation administration of N-acetylcysteine reduces cerebral HPO production and oxidative stress, probably through a taurine-related mechanism.

The hemodynamic effects of dobutamine during reoxygenation after hypoxia: a dose-response study in newborn pigs

Asphyxiated neonates usually have myocardial stunning and hypotension and require inotropic support. A randomized controlled study was designed to examine the dose-response effect of dobutamine (5-20 microg x kg(-1) x min(-1)) on systemic and regional circulations and oxygen metabolism in a neonatal swine model of hypoxia/reoxygenation. Thirty-eight anesthetized newborn piglets were acutely instrumented for continuous monitoring of heart rate, systemic and pulmonary arterial pressures, and pulmonary (surrogate for cardiac index), right common carotid, and superior mesenteric and left renal arterial flows. After stabilization, they were exposed to normocapnic alveolar hypoxia (10%-15% oxygen) for 2 h followed by reoxygenation with 100% oxygen for 1 h, then 21% for 3 h. Piglets were block randomized to receive dobutamine infusion (5, 10, or 20 microg x kg(-1) x min(-1)) or saline (control) at 2 to 4 h of reoxygenation (n = 8 each). A nonasphyxiated, sham-operated group was included (n = 6). Blood samples were collected for blood gas analysis, arterial and venous co-oximetry, and plasma lactate concentration determination. At 2-h reoxygenation after hypoxia, there was hypotension (systemic arterial pressure, 27 to 36 mmHg) and myocardial dysfunction (cardiac index from 178-209 to 134-156 mL x kg(-1) x min(-1)). Cardiac index improved significantly with 20 microg x kg(-1) x min(-1) of dobutamine (P < 0.05) and modestly in the treatment groups of 5 and 10 microg x kg(-1) x min(-1) (P < 0.1) (at 120 min, 172 +/- 35, 160 +/- 30, and 158 +/- 56 mL x kg(-1) x min(-1) vs. 119 +/- 33 mL x kg(-1) x min(-1) of controls, respectively), with corresponding increases in stroke volume. Pulmonary vascular resistance was lower in all dobutamine-treated groups (vs. controls, P < 0.05) There were no differences in heart rate, systemic and pulmonary arterial pressures, systemic vascular resistance, and regional flows between groups. The group of 20 mug.kg.min of dobutamine also had higher systemic oxygen delivery (at 120 min, 18 +/- 5 vs. 11 +/- 3 O(2) mL x kg(-1) x min(-1) of controls, P < 0.05) with no significant differences in systemic oxygen consumption and regional oxygen delivery between groups. After the reoxygenation of newborn piglets with severe hypoxia, high dose of dobutamine is effective to treat myocardial stunning and low cardiac output with no significant effect on blood pressure or regional circulation. Further clinical studies are needed to confirm these findings in the human neonate.

Expression of angiostatin and its related factors in the plasma of newborn pigs with hypoxia and reoxygenation

Little is known about angiostatin and its related factors in the hypoxia-reoxygenation of neonates. In this study we compared the effect of 21% and 100% reoxygenation on temporal changes in the plasma level of these factors in newborn piglets subjected to hypoxia. Newborn piglets were subjected to 2 h hypoxia followed by 1 h of reoxygenation with either 21% or 100% oxygen and observed for 4 days. On day 4 of recovery in 100% hypoxic-reoxygenated group, there were increases in total angiostatin, plasminogen/plasmin and MMP-2 levels, and decreases in VEGF levels (vs. respective baseline levels, all P <0.001), whereas no significant temporal changes were found in the 21% hypoxic-reoxygenated and sham-operated groups. Angiostatin levels correlated positively with the levels of MMP-2 and HIF-1alpha and negatively with VEGF levels in 100% hypoxic-reoxygenated group (all P <0.05). In comparison to 21% oxygen, neonatal resuscitation with 100% oxygen was found to increase the levels anti-angiogenic factors.

Nursing update on retinopathy of prematurity

One of the problems that plagues premature infants is retinopathy of prematurity, a potentially blinding disease that occurs because the retina is immature before 34 weeks gestation and must develop in a suboptimal environment when a baby is born early. Prevention by minimizing oxygen exposure has been somewhat effective, but survival of the tiniest babies has led to a recent resurgence in cases. Oxygen targeting and early surgery show promise to reduce the risk of blindness in the smallest premature infants. Nurses play an important role in oxygen management and parental support.

RESUSCITATION WITH 21% OR 100% OXYGEN IS EQUALLY EFFECTIVE IN RESTORING PERFUSION AND OXYGEN METABOLISM IN THE LIVER OF HYPOXIC NEWBORN PIGLETS

The differential effects of the use of high or low oxygen levels during resuscitation on the neonatal liver are unknown. We compared the hepatic hemodynamics and oxygen metabolism in hypoxic newborn piglets resuscitated with 21% or 100% oxygen. Twenty-seven piglets (age, 1-3 days; weight, 1.5-2.0 kg) were acutely instrumented to measure cardiac output, hepatic artery, and portal venous blood flows (hepatic artery flow index [HAFI] and portal venous flow index [PVFI], respectively). The animals underwent 2 h of hypoxia (fraction of inspired oxygen, 0.10-0.15), then reoxygenation with 21% (n = 9) or 100% (n = 9) oxygen for 1 h, then 1 h with 21% oxygen. The controls (n = 9) were sham-operated without hypoxia-reoxygenation. Oxygen transport and plasma lactate concentrations were studied. Hypoxic animals had hypotension and decreased cardiac index with metabolic acidosis (mean pH, 7.00-7.02; P < 0.05 vs. controls). The PVFI and the total hepatic blood flow (THFI = PVFI + HAFI), despite the absence of significant change in HAFI, decreased to 16 +/- 2 mL/min/kg and 19 +/- 3 mL/min/kg, respectively (versus 24 +/- 2 mL/min/kg and 28 +/- 2 mL/min/kg of controls; P < 0.05). Fifteen minutes after reoxygenation, the cardiac index improved, PVFI recovered, HAFI was maintained, and THFI was not different between the groups. The hepatic oxygen consumption decreased (59%; P < 0.05) and the extraction increased (89%; P < 0.001) during hypoxia. Similarly, on reoxygenation, the hepatic oxygen consumption improved; however, extraction decreased versus controls on 100% but not on 21% oxygen (P < 0.05). The plasma lactate concentrations increased in both groups with hypoxia and were not different during reoxygenation between the group administered with 21% oxygen and the group administered with 100% oxygen. The hypoxic neonatal liver has reduced hepatic blood flow but has relatively preserved HAFI, and oxygen consumption recovered similarly on reoxygenation with 21% and 100% oxygen. The increased oxygen extraction during hypoxia normalized in 21% but reduced in 100% reoxygenation, with no differences in plasma lactate concentrations.

TEMPORAL PLATELET AGGREGATORY FUNCTION IN HYPOXIC NEWBORN PIGLETS REOXYGENATED WITH 18%, 21%, AND 100% OXYGEN

Thromboembolic and bleeding complications are common after asphyxia. We studied the temporal effects of different oxygen concentrations used in resuscitating hypoxic newborn piglets on platelet aggregatory function. Alveolar normocapnic hypoxia (fractional inspired oxygen concentration = 0.15) was induced in piglets (1-4 d, 1.7-2.5 kg) for 2 h, followed by reoxygenation with 18%, 21%, or 100% oxygen for 1 h and then 21% for 2 h (n = 8-9 per group). Control piglets underwent surgery with no hypoxia-reoxygenation (n = 5). Platelet counts and collagen-stimulated (2-10 microg/mL) whole blood aggregation were studied at normoxic baseline and at 3 h, 2 d, and 4 d of recovery. Platelet activation markers including plasma thromboxane B2 and matrix metalloproteinase 2 and 9 levels were measured. At 2 h hypoxia (mean PaO2 30-35 mmHg), all piglets were hypotensive and acidotic (mean pH 7.19-7.24). In 100% reoxygenation piglets, the concentration-response curves of collagen-stimulated platelet aggregation were significantly shifted upward at 3 h and 2 d of recovery with no differences in the collagen concentration required to induce 50% of maximum aggregation, and this normalized to baseline on 4 d. In the 18% and 21% reoxygenated groups, there were no changes in platelet aggregation during the experiment. Platelet counts were not different between groups and over time. Hypoxic-reoxygenated piglets had increased plasma thromboxane B2 (100% group) and matrix metalloproteinase-2 levels (21% and 100% groups) (versus respective baseline, P < 0.05), with no difference between experimental groups. These findings suggest transient platelet activation in hypoxic newborn piglets resuscitated with 100% but not with 18% and 21% oxygen, of which the clinical significance requires further investigation.

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.

Evaluation and development of potentially better practices to reduce bronchopulmonary dysplasia in very low birth weight infants

OBJECTIVE

The objective of this study was to describe development and implementation of potentially better practices to reduce bronchopulmonary dysplasia in very low birth weight infants (birth weight: 501-1500 g).

METHODS

Results of Breathsavers Group meetings, conference calls and critically appraised topic summaries were used to construct potentially better practices. Implementation plans and experiences were reported by participants and collated.

RESULTS

The Breathsavers Group developed 13 potentially better practices, based on published evidence and expert opinion. Participants determined which potentially better practices to implement and implementation methods. Participating NICUs implemented an average of 5 potentially better practices (range: 3-9). The Breathsavers Group also developed a resource kit, identified common obstacles to implementation, and initiated research to define bronchopulmonary dysplasia better.

CONCLUSIONS

Multiinstitutional collaboration facilitated development and implementation of potentially better practices to reduce bronchopulmonary dysplasia.

Platelet dysfunction in asphyxiated newborn piglets resuscitated with 21% and 100% oxygen

Hemostatic disturbances are common in asphyxiated newborns after resuscitation. We compared platelet function in hypoxic newborn piglets reoxygenated with 21% or 100% oxygen. Piglets (1-3 d, 1.5-2.1 kg) were anesthetized and acutely instrumented for hemodynamic monitoring. After stabilization, normocapnic hypoxia was induced with an inspired oxygen concentration of 10-15% for 2 h. Piglets were then resuscitated for 1 h with 21% or 100% oxygen, followed by 3 h with 21% oxygen. Platelet counts and collagen (2, 5, and 10 microg/mL)-stimulated whole blood aggregation were studied before hypoxia and at 4 h of post-hypoxia/reoxygenation. Platelet function was studied using transmission electron microscopy and by measuring plasma thromboxane B2 (TxB2) and matrix metalloproteinase (MMP)-2 and -9 levels. Control piglets were sham-operated without hypoxia/reoxygenation. The hypoxemic (PaO2 33 mm Hg) piglets developed hypotension with metabolic acidosis (pH 7.02-7.05). Upon reoxygenation, piglets recovered and blood gases gradually normalized. At 4 h reoxygenation, platelet aggregation ex vivo was impaired as evidenced by a rightward-downward shifting of the concentration-response curves. Electron microscopy showed features of platelet activation. Plasma MMP-9 but not MMP-2 activity significantly increased. Resuscitation with 100% but not 21% oxygen increased plasma TxB2 levels. Platelet counts decreased after hypoxia/reoxygenation but were not different between groups during the experiment. Resuscitation of hypoxic newborn piglets caused platelet activation with significant deterioration of platelet aggregation ex vivo and increased plasma MMP-9 levels. High oxygen concentrations may aggravate the activation of prostaglandin-thromboxane mechanistic pathway.

Oxidative Stress in the Newborn – A 30-Year Perspective

In this review the development of the concept 'hypoxia-reoxygenation injury' is outlined. An update of some important factors and mechanisms related to oxidative stress injury in newborn infants is presented, including the metabolism of glutathione, the role of antioxidants, iron and nitric oxide, and how these may influence health and disease in the newborn and contribute to 'oxygen radical disease of the newborn'. New insight into how hyperoxia and hypoxia may induce changes leading to retinopathy of prematurity by vascular endothelial growth factor acting in concert with insulin-like growth factor is briefly summarized. Inflammation and oxidative stress seem to be two sides of the same coin in newborn babies both contributing to injury partly through similar mechanisms.

Cardiac function, myocardial glutathione, and matrix metalloproteinase-2 levels in hypoxic newborn pigs reoxygenated by 21%, 50%, or 100% oxygen

After asphyxia, it is standard to resuscitate the newborn with 100% oxygen, which may create a hypoxia-reoxygenation process that may contribute to subsequent myocardial dysfunction. We examined the effects of graded reoxygenation on cardiac function, myocardial glutathione levels, and matrix metalloproteinase (MMP)-2 activity during recovery. Thirty-two piglets (1-3 days old, weighing 1.5-2.1 kg) were anesthetized and instrumented for continuous monitoring of cardiac index, and systemic and pulmonary arterial pressures. After 2 h of hypoxia, piglets were randomized to receive reoxygenation for 1 h with 21%, 50%, or 100% oxygen (n = 8 each), followed by 3 h at 21% oxygen. At 2 h of hypoxemia (PaO2 32-34 mmHg), the animals had hypotension, decreased cardiac index, and elevated pulmonary arterial pressure (P < 0.001 vs. controls). Upon reoxygenation, cardiac function recovered in all groups with higher cardiac index and lower systemic vascular resistance in the 21% group at 30 min of reoxygenation (P < 0.05 vs. controls). Pulmonary artery pressure normalized in an oxygen-dependent fashion (100% = 50% > 21%), despite an immediate recovery of pulmonary vascular resistance in all groups. The hypoxia-reoxygenated (21%-100%) hearts had similarly increased MMP-2 activity and decreased glutathione levels (P < 0.05, 100% vs. controls), which correlated significantly with cardiac index and stroke volume during reoxygenation, and similar features of early myocardial necrosis. In neonatal resuscitation, if used with caution because of a slower resolution of pulmonary hypertension, 21% reoxygenation results in similar cardiac function and early myocardial injury as 50% or 100%. The significance of higher oxidative stress with high oxygen concentration is unknown, at least in the acute recovery period.