Is oxygen more toxic than currently believed?

Can hyperoxic stress cause susceptibility to acute seizure in the neonatal period?: a rat study

Objective: Preterm neonates encounter hyperoxia relatively early, and are more exposed to hyperoxic stress due to their insufficient antioxidant defense mechanisms. This study was planned around the hypothesis that this hyperoxic effect may cause a disposition to future acute seizures. Methods: This study was composed of two main groups Hyperoxy and Control (Room air with normal O2 levels) Groups. Group 1 - hyperoxia (Study): The experimental group consisted of premature newborn rats exposed to hyperoxia with their dams from birth to postnatal day 5. Group 2 - room air (Control): The group was not exposed to hyperoxia and housed the same room air and temperature as their dams. Female, Acute Epilepsy Female, Male, Acute Epilepsy Male, and a total of eight subgroups were formed in both the control and hyperoxia groups. When the rats were two months old, intracranial electrodes were attached to obtain electrocorticography (ECoG) recordings. Pre-model recordings were taken, after which an acute pentylenetetrazole (PTZ) model of absence seizure was induced by the intraperitoneal administration of PTZ at 50 mg/kg. ECoG records were examined using the PowerLab system for 180 min. Spike wave number and duration, Spike wave frequency and amplitude data were evaluated.Results: Seven female and three male rats were exposed to hyperoxia, and a control group of five female and three male rats were included in the study. The median interquartile range for spike wave latency in the hyperoxia and control groups were 1112 (644-1545) and 654 (408-1152), frequency 4476 (3120-7421) and 3934 (2264-4704), and amplitude data 0.68 (0.59-0.79) and 0.52 (0.37-0.67), respectively. Although a difference was observed in median values capable of constituting susceptibility to epilepsy, the difference was not statistically significant (p > 0.05). In terms of gender, spike-wave counts were significantly higher in female rats (p < 0.05). Females exposed to hyperoxia were more susceptible to epilepsy than both males and females in the control group (p < 0.05).Conclusion: Exposure to hyperoxia in the first days of life of premature neonates due to their susceptibility to oxidative stress and insufficient antioxidant mechanisms, can cause a disposition to acute seizures. As a result, females exposed to hyperoxia during the neonatal period may be prone to epilepsy in maturity.

Oxygenation of the newborn. The impact of one molecule on newborn lives

Hypoxanthine is a purine metabolite which increases during hypoxia and therefore is an indicator of this condition. Further, when hypoxanthine is oxidized to uric acid in the presence of xanthine oxidase, oxygen radicals are generated. This was the theoretical basis for suggesting and studying, beginning in the 1990s, resuscitation of newborn infants with air instead of the traditional 100% O2. These studies demonstrated a 30% reduction in mortality when resuscitation of term and near term infants was carried out with air compared to pure oxygen. The mechanism for this is not fully understood, however the hypoxanthine -xanthine oxidase system increases oxidative stress and plays a role in regulation of the perinatal circulation. Further, hyperoxic resuscitation inhibits mitochondrial function, and one reason may be that genes involved in ATP production are down-regulated. Thus, the study of one single molecule, hypoxanthine, has contributed to the global prevention of an estimated 2-500,000 annual infant deaths.

The retinal vascular growth rate in babies with retinopathy of prematurity could indicate treatment need

Purpose

To analyze the weekly rate of retinal vascular growth in treatment-naïve babies with various stages of retinopathy of prematurity (ROP) and validate if this could be a predictor of treatment need.

Methods

Retrospective review of medical charts and retinal images of babies with various stages of ROP. The images were enhanced using red-green image enhancement software. Using the length of the horizontal disc diameter (DD) of each eye, the vessel growth was measured from the disc margin up to the vessel tip in fixed quadrants. The rate of vessel growth was the ratio of vessel length to the number of weeks it took to reach this length. The babies were divided into treatment warranting ROP (group 1), low-risk pre-threshold (type II) ROP (group 2,), and no-ROP (group 3) for analysis. The "no-ROP" group acted as normal control. Group 1 was further subdivided into 1A (threshold ROP), IB (aggressive posterior ROP), 1C (hybrid ROP), and ID (high-risk pre-threshold ROP).

Results

Out of 436 eyes, groups 1, 2, and 3 had 238, 108, and 90 eyes, respectively. The mean rate of vascular outgrowth along with 95% confidence interval (CI) was 0.490 [0.487,0.520], 0.612 [0.599, 0.638], and 0.719 [0.703, 0.740] DD/week, respectively, for babies with "treatment warranting," "low risk pre-threshold" and "no ROP" groups, respectively. In our estimate, more than 80% of eyes with a vessel growth rate of 0.54 DD/week or less required treatment.

Conclusion

A rate of retinal vascular growth less than 0.54 DD/week can be used to determine treatment requirements in babies with ROP.

Short exposure to hyperoxia causes cultured lung epithelial cell mitochondrial dysregulation and alveolar simplification in mice

BACKGROUND

Prolonged exposure to high oxygen concentrations in premature infants, although lifesaving, can induce lung oxidative stress and increase the risk of developing BPD, a form of chronic lung disease. The lung alveolar epithelium is damaged by sustained hyperoxia, causing oxidative stress and alveolar simplification; however, it is unclear what duration of exposure to hyperoxia negatively impacts cellular function.

METHODS

Here we investigated the role of a very short exposure to hyperoxia (95% O₂, 5% CO₂) on mitochondrial function in cultured mouse lung epithelial cells and neonatal mice.

RESULTS

In epithelial cells, 4 h of hyperoxia reduced oxidative phosphorylation, respiratory complex I and IV activity, utilization of mitochondrial metabolites, and caused mitochondria to form elongated tubular networks. Cells allowed to recover in air for 24 h exhibited a persistent global reduction in fuel utilization. In addition, neonatal mice exposed to hyperoxia for only 12 h demonstrated alveolar simplification at postnatal day 14.

CONCLUSION

A short exposure to hyperoxia leads to changes in lung cell mitochondrial metabolism and dynamics and has a long-term impact on alveolarization. These findings may help inform our understanding and treatment of chronic lung disease.

IMPACT

Many studies use long exposures (up to 14 days) to hyperoxia to mimic neonatal chronic lung disease. We show that even a very short exposure to hyperoxia leads to long-term cellular injury in type II-like epithelial cells. This study demonstrates that a short (4 h) period of hyperoxia has long-term residual effects on cellular metabolism. We show that neonatal mice exposed to hyperoxia for a short time (12 h) demonstrate later alveolar simplification. This work suggests that any exposure to clinical hyperoxia leads to persistent lung dysfunction.

Nup133 and ERα mediate the differential effects of hyperoxia-induced damage in male and female OPCs

Background

Hyperoxia is a well-known cause of cerebral white matter injury in preterm infants with male sex being an independent and critical risk factor for poor neurodevelopmental outcome. Sex is therefore being widely considered as one of the major decisive factors for prognosis and treatment of these infants. But unfortunately, we still lack a clear view of the molecular mechanisms that lead to such a profound difference. Hence, using mouse-derived primary oligodendrocyte progenitor cells (OPCs), we investigated the molecular factors and underlying mechanisms behind the differential response of male and female cells towards oxidative stress.

Results

We demonstrate that oxidative stress severely affects cellular functions related to energy metabolism, stress response, and maturation in the male-derived OPCs, whereas the female cells remain largely unaffected. CNPase protein level was found to decline following hyperoxia in male but not in female cells. This impairment of maturation was accompanied by the downregulation of nucleoporin and nuclear lamina proteins in the male cells. We identify Nup133 as a novel target protein affected by hyperoxia, whose inverse regulation may mediate this differential response in the male and female cells. Nup133 protein level declined following hyperoxia in male but not in female cells. We show that nuclear respiratory factor 1 (Nrf1) is a direct downstream target of Nup133 and that Nrf1 mRNA declines following hyperoxia in male but not in female cells. The female cells may be rendered resistant due to synergistic protection via the estrogen receptor alpha (ERα) which was upregulated following hyperoxia in female but not in male cells. Both Nup133 and ERα regulate mitochondrial function and oxidative stress response by transcriptional regulation of Nrf1.

Conclusions

These findings from a basic cell culture model establish prominent sex-based differences and suggest a novel mechanism involved in the differential response of OPCs towards oxidative stress. It conveys a strong message supporting the need to study how complex cellular processes are regulated differently in male and female brains during development and for a better understanding of how the brain copes up with different forms of stress after preterm birth.

Oxygen metabolism and oxygenation of the newborn

The premature infant is to some extent protected from hypoxia, however defense against hyperoxia is poorly developed. The optimal assessment of oxygenation is to measure oxygen delivery and extraction. At the bedside PaO₂ and SpO₂ are approximations of oxygenation at the tissue level. After birth asphyxia it is crucial to know whether or not to give oxygen supplementation, when, how much, and for how long. Oxygen saturation targets in the delivery room have been studied, but the optimal targets might still be unknown because factors like gender and delayed cord clamping influence saturation levels. However, SpO₂ > 80% at 5 min of age is associated with favorable long term outcome in preterm babies. Immature infants most often need oxygen supplementation beyond the delivery room. Predefined saturation levels, and narrow alarm limits together with the total oxygen exposure may impact on development of oxygen related diseases like ROP and BPD. Hyperoxia is a strong trigger for genetic and epigenetic changes, contributing to the development of these conditions and perhaps lifelong changes.

Oxygen radical disease in the newborn, revisited: Oxidative stress and disease in the newborn period

Thirty years ago, there was an emerging appreciation for the significance of oxidative stress in newborn disease. This prompted a renewed interest in the impact of oxygen therapy for the newborn in the delivery room and beyond, especially in premature infants. Today, the complexity of oxidative stress both in normal regulation and pathology is better understood, especially as it relates to neonatal mitochondrial oxidative stress responses to hyperoxia. Mitochondria are recipients of oxidative damage and have a propensity for oxidative self-injury that has been implicated in the pathogenesis of neonatal lung diseases. Similarly, both intrauterine growth restriction (IUGR) and macrosomia are associated with mitochondrial dysfunction and oxidative stress. Additionally, reoxygenation with 100% O₂ in a hypoxic-ischemic newborn lamb model increased the production of pro-inflammatory cytokines in the brain. Moreover, the interplay between inflammation and oxidative stress in the newborn is better understood because of animal studies. Transcriptomic analyses have found a number of genes to be differentially expressed in murine models of bronchopulmonary dysplasia (BPD). Epigenetic changes have also been detected both in animal models of BPD and premature infants exposed to oxygen. Antioxidant therapy to prevent newborn disease has not been very successful; however, new therapeutic principles, like melatonin, are under investigation.

Primary prevention of ROP and the oxygen saturation targeting trials

Reducing the burden of visual morbidity from retinopathy of prematurity (ROP) begins with primary prevention, and improvements in neonatal care with a positive impact on ROP are possible in all settings. Strategies range from rigorous adoption of inexpensive evidence-based protocols, for example on temperature control, prevention of sepsis and support for breast-milk feeding, through to comprehensive quality improvement programmes, and fostering team work and camaraderie. Oxygen monitoring is essential for very preterm infants receiving supplementary oxygen. The Neonatal Oxygenation Prospective Meta-analysis (NeOProM) collaboration has reported analysis of five trials of oxygen saturation (SpO₂) targeting in very preterm infants and shown that a SpO₂ target of 85-89% compared to 91-95% was associated with increased mortality (on average 28 extra deaths for every 1000 infants treated). Adopting a SpO₂ target higher than 85-89% might increase the risk of ROP for some infants, highlighting the importance of pursuing all other means of prevention.

Incidence and risk factors of retinopathy of prematurity and utility of the national screening criteria in a tertiary center in Iran

AIM

To determine the incidence and risk factors of retinopathy of prematurity (ROP) and the sensitivity of current screening criteria in a tertiary eye center in Tehran, Iran.

METHODS

In a cross-sectional observational study, neonates weighing ≤2000 grams at birth or born <34wk gestational age (GA) and all other infants at risk of ROP admitted to the neonatal intensive care unit (NICU) or referred to our ROP clinic were investigated. The incidence of ROP and severe ROP (i.e. patients needing treatment) were determined. The associations between risk factors and the development and severity of ROP were assessed. We also examined the sensitivity of the current national screening guideline in Iran.

RESULTS

Among 207 infants, the incidence of ROP and severe ROP was 33.3% and 11.1%, respectively. Mean GA and birth weight (BW) were significantly lower in ROP vs non-ROP infants (29±2wk vs 33±3wk, P<0.001; 1274±489 g vs 1916±550 g, P<0.001, respectively). Univariate analysis displayed significant association between ROP incidence and GA, BW, NICU admission period, blood transfusion, surfactant usage, sepsis, intraventricular hemorrhage and patent ductus arteriosus (P<0.05 for all). BW [relative risk (RR): 0.857 (0.711-0.873), P<0.001], GA [RR: 0.788 (0.711-0.873), P<0.001] and blood transfusion [RR: 1.888 (0.995-3.583), P=0.052] were independent ROP risk factors. The sensitivity of country-specific screening guidelines was 95.7% and 100% for overall and severe ROP detection, respectively.

CONCLUSION

ROP incidence is relatively high in Iran. Identifying ROP risk factors results in more accurate screening and reduces the risk of irreversible vision loss. The ROP screening criteria utilized in Iran are efficient at the present time.

The fetal circulation, pathophysiology of hypoxemic respiratory failure and pulmonary hypertension in neonates, and the role of oxygen therapy

Neonatal hypoxemic respiratory failure (HRF), a deficiency of oxygenation associated with insufficient ventilation, can occur due to a variety of etiologies. HRF can result when pulmonary vascular resistance (PVR) fails to decrease at birth, leading to persistent pulmonary hypertension of newborn (PPHN), or as a result of various lung disorders including congenital abnormalities such as diaphragmatic hernia, and disorders of transition such as respiratory distress syndrome, transient tachypnea of newborn and perinatal asphyxia. PVR changes throughout fetal life, evident by the dynamic changes in pulmonary blood flow at different gestational ages. Pulmonary vascular transition at birth requires an interplay between multiple vasoactive mediators such as nitric oxide, which can be potentially inactivated by superoxide anions. Superoxide anions have a key role in the pathophysiology of HRF. Oxygen (O2) therapy, used in newborns long before our knowledge of the complex nature of HRF and PPHN, has continued to evolve. Over time has come the discovery that too much O2 can be toxic. Recommendations on the optimal inspired O2 levels to initiate resuscitation in term newborns have ranged from 100% (pre 1998) to the currently recommended use of room air (21%). Questions remain about the most effective levels, particularly in preterm and low birth weight newborns. Attaining the appropriate balance between hypoxemia and hyperoxemia, and targeting treatments to the pathophysiology of HRF in each individual newborn are critical factors in the development of improved therapies to optimize outcomes.

Incidence and Risk Factors for Retinopathy of Prematurity in North of Iran

Purpose:

To report the incidence and risk factors for retinopathy of prematurity (ROP) among preterm infants referred to Amiralmomenin Eye Hospital, Rasht, Iran.

Methods:

This cross-sectional retrospective study included all preterm infants with birth weight ≤2500 g and/or gestational age ≤36 weeks who had been referred to our facility for ROP screening over a five year period from September 2005 to September 2010. Possible risk factors and findings related to eye examinations were extracted and analyzed.

Results:

Among 310 infants, ROP was diagnosed in 64 (20.6%) of referred preterm infants (95% CI: 17.7%-23.5%); these included stage I in 48%, stage 2 in 29%, and stage 3 or higher disease in 23% of subjects. Mean gestational age (GA) and birth weight (BW) in the ROP–affected infants was 30.18 ± 2.28 weeks and 1,422.8 ± 420.8 g, respectively. Low BW, low GA, oxygen therapy, phototherapy, blood transfusion and apnea were risk factors for ROP. After logistic regression analysis, only low GA and low BW were independently associated with the condition.

Conclusion:

ROP is a relatively common finding in preterm infants of Guilan Province in the North of Iran. Low BW and low GA were significant risk factors for the disease.

Zonisamide attenuates hyperoxia-induced apoptosis in the developing rat brain

Oxygen therapy used in the treatment of perinatal hypoxia induces neurodegeneration in babies with immature antioxidant mechanisms. Zonisamide is a new antiepileptic drug used in childhood intractable seizures. Many studies demonstrated its neuroprotective effects. There is no study evaluating its effect on hyperoxic brain injury. The aim of this study was to investigate the neuroprotective effect of zonisamide on hyperoxia-induced neonatal brain injury. A total of 21 Wistar rat pups were used. The animals were divided into three groups: control group, hyperoxia group, and zonisamide-treated group. The zonisamide-treated group received an intraperitoneal injection of zonisamide. Zonisamide significantly preserved the number of neurons in CA1 and dentate gyrus parts of hippocampus, prefrontal, and parietal cortex. Zonisamide treatment also decreased the number of apoptotic neurons in all examined parts of hippocampus, prefrontal, and parietal cortex. We suggest that zonisamide treatment may be used as a neuroprotective agent in hyperoxic brain injury.

Transcriptome profiling of the newborn mouse lung after hypoxia and reoxygenation: hyperoxic reoxygenation affects mTOR signaling pathway, DNA repair, and JNK-pathway regulation

BACKGROUND

The use of oxygen in acute treatment of asphyxiated term newborns is associated with increased mortality. It is unclear how hyperoxic reoxygenation after hypoxia affects transcriptional changes in the newborn lung.

METHODS

On postnatal day 7, C57BL/6 mice (n = 62) were randomized to 120-min hypoxia (fraction of inspired oxygen (FiO2) 0.08) or normoxia. The hypoxia group was further randomized to reoxygenation for 30 min with FiO2 0.21, 0.40, 0.60, or 1.00, and the normoxia group to FiO2 0.21 or 1.00. Transcriptome profiling was performed on homogenized lung tissue using the Affymetrix 750k expression array, and validation was carried out by real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

The hypoxia-reoxygenation model induced hypoxia-inducible factor 1 (HIF-1) targets like Vegfc, Adm, and Aqp1. In total, ~70% of the significantly differentially expressed genes were detected in the two high hyperoxic groups (FiO2 0.60 and 1.00). Reoxygenation with 100% oxygen after hypoxia uniquely upregulated Gadd45g, Dusp1, Peg3, and Tgm2. Pathway analysis identified mammalian target of rapamycin (mTOR) signaling pathway, DNA repair, c-jun N-terminal kinase (JNK)-pathway regulation, and cell cycle after hyperoxic reoxygenation was applied.

CONCLUSION

Acute hypoxia induces HIF-1 targets independent of the reoxygenation regime applied. Hyperoxic reoxygenation affects pathways regulating cell growth and survival. DNA-damage-responsive genes are restricted to reoxygenation with 100% oxygen.

Incidence and risk factors of retinopathy of prematurity in mashhad, northeast iran

BACKGROUND

Retinopathy of prematurity (ROP) is a vascular retinal disease that can cause low vision or blindness and affects premature newborns of very low birth weight.

OBJECTIVES

The purpose of this study was to determine the incidence and risk factors for ROP among very premature infants in Mashhad located northeast of Iran.

MATERIAL AND METHODS

In this cross-sectional study performed between 2006 and 2010, predisposing factors and severity of ROP were evaluated in very premature infants (<32 gestational weeks). Consecutive infants were enrolled at birth and screened for ROP at 4 to 6 weeks of age by indirect ophthalmoscopy. Severe ROP was defined as stage 4 or 5. Chi-square, Student's t-, and Fisher's test were used for statistical analysis.

RESULTS

The incidence of ROP was 26.2%. Significant differences between the ROP and control groups were observed, these include; gestational age, sex, birth weight, Apgar score, durationof parenteral nutrition, oxygen therapy, phototherapy, maximum PaO2 and minimum SpO2 (P < 0.05). Severe ROP was seen in 31.4% (11/32) of ROP cases (5.4% of newborns).

CONCLUSION

The incidence of ROP is relatively high in this region. Risk factors for ROP among very premature infants include hypoxia, severe hyperoxia, relatively low blood SPO2, gestational age, birth weight, and Apgar score.

Dynamic FDG PET for assessing early effects of cerebral hypoxia and resuscitation in new-born pigs

PURPOSE

Changes in cerebral glucose metabolism may be an early prognostic indicator of perinatal hypoxic-ischaemic injury. In this study dynamic ¹⁸F-FDG PET was used to evaluate cerebral glucose metabolism in piglets after global perinatal hypoxia and the impact of the resuscitation strategy using room air or hyperoxia.

METHODS

New-born piglets (n = 16) underwent 60 min of global hypoxia followed by 30 min of resuscitation with a fraction of inspired oxygen (FiO₂) of 0.21 or 1.0. Dynamic FDG PET, using a microPET system, was performed at baseline and repeated at the end of resuscitation under stabilized haemodynamic conditions. MRI at 3 T was performed for anatomic correlation. Global and regional cerebral metabolic rates of glucose (CMRgl) were assessed by Patlak analysis for the two time-points and resuscitation groups.

RESULTS

Global hypoxia was found to cause an immediate decrease in cerebral glucose metabolism from a baseline level (mean ± SD) of 21.2 ± 7.9 to 12.6 ± 4.7 μmol/min/ 100 g (p <0.01). The basal ganglia, cerebellum and cortex showed the greatest decrease in CMRgl but no significant differences in global or regional CMRgl between the resuscitation groups were found.

CONCLUSION

Dynamic FDG PET detected decreased cerebral glucose metabolism early after perinatal hypoxia in piglets. The decrease in CMRgl may indicate early changes of mild cerebral hypoxia-ischaemia. No significant effect of hyperoxic resuscitation on the degree of hypometabolism was found in this early phase after hypoxia. Cerebral FDG PET can provide new insights into mechanisms of perinatal hypoxic- ischaemic injury where early detection plays an important role in instituting therapy.

Hyperoxia in the term newborn: more evidence is still needed for optimal oxygen therapy

It took more than 30 years from the first observations that oxygen may be toxic during resuscitation till international guidelines changed to recommend that term and near term newborn infants should be resuscitated with air instead of 100% oxygen. There are still a number of unanswered questions related to oxygen therapy of the newborn infant. The newborn brain, lungs and other organs are susceptible to oxygen injury, and newborns still develop injury caused by hyperoxia.

Maternal prenatal omega-3 fatty acid supplementation attenuates hyperoxia-induced apoptosis in the developing rat brain

Supraphysiologic amounts of oxygen negatively influences brain maturation and development. The aim of the present study was to evaluate whether maternal ω-3 long-chain polyunsaturated fatty acid (ω-3 FA) supplementation during pregnancy protects the developing brain against hyperoxic injury. Thirty-six rat pups from six different dams were divided into six groups according to the diet modifications and hyperoxia exposure. The groups were: a control group (standard diet+room air), a hyperoxia group (standard diet+80% O₂ exposure), a hyperoxia+high-dose ω-3 FA-supplemented group, a hyperoxia+low-dose ω-3 FA-supplemented group, a room air+low-dose ω-3 FA-supplemented+group, and a room air+high dose ω-3 FA-supplemented group. The ω-3 FA's were supplemented as a mixture of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) from the second day of pregnancy until birth. Rat pups in the hyperoxic groups were exposed to 80% oxygen from birth until postnatal day 5 (P5). At P5, all animals were sacrificed. Neuronal cell death and apoptosis were evaluated by cell count, TUNEL, and active Caspase-3 immunohistochemistry. Histopathological examination showed that maternally ω-3 FA deficient diet and postnatal hyperoxia exposure were associated with significantly lower neuronal counts and significantly higher apoptotic cell death in the selected brain regions. Ω-3 FA treatment significantly diminished apoptosis, in the selected brain regions, in a dose dependent manner. Our results suggest that the maternal ω-3 FA supply may protect the developing brain against hyperoxic injury.

Analysis of incidence and risk factors of retinopathy of prematurity among very-low-birth-weight infants in North Taiwan

BACKGROUND

Although significant advances have been made in perinatal care, retinopathy of prematurity (ROP) remains a serious complication in prematurely born individuals. There have been limited studies on ROP in Taiwan, and most of those existing reports are outdated.

METHODS

This retrospective study included 252 very-low-birth-weight (VLBW) infants admitted to the neonatal intensive care unit of Chang Gung Children's Hospital over a 2-year period between July 2005 and June 2007. All infants were examined for ROP according to the guidelines published by the American Academy of Pediatrics. The relationship between clinical risk factors and the development of ROP was analyzed.

RESULTS

Of the 252 VLBW infants, 216 met the screening criteria. Of the 216, 99 (45.8%) had ROP. Compared with neonates born at 29 weeks of gestational age (GA) or later, those very premature infants of ≤25 weeks' and 26-28 weeks' GA had increased odds ratios (OR) of 8.49 and 3.19, respectively, for the development of severe ROP. No ROP was detected in infants of greater than 33 weeks' GA. The simultaneous presence of a low GA, low birth weight (LBW), lower Apgar scores, hypotension, patent ductus arteriosus, septicemia, intraventricular hemorrhage, ventilator dependence, and use of postnatal steroids was associated with severe ROP. Using multiple logistic regression analyses for ROP, only maternal preeclampsia [OR, 2.52; confidence interval (CI), 1.32-4.7]; duration of mechanical ventilation (OR, 1.06; CI, 1.04-1.08); and LBW (OR, 2.62; CI, 1.370-3.375) predicted the development of threshold ROP.

CONCLUSION

The incidence of ROP among VLBW infants was 45.8%; 19.0% had severe ROP. Infants of lower GAs and/or with LBW, whose mother had preeclampsia or who had a long duration of mechanical ventilation are at risk for the development of threshold ROP.

Maintaining optimal oxygen saturation in premature infants

INTRODUCTION

Advances in technology have resulted in increasing survival rates for premature infants. Oxygen therapy is commonly used in neonatal units as part of respiratory support. The number of premature infants in our institution surviving with severe (stage ≥3) retinopathy of prematurity (ROP) prompted a review of oxygen therapy as a contributing factor. Prolonged exposure to high concentrations of oxygen may cause irreversible damage to the eyes of very-low-birth-weight preterm infants and is a potential cause of blindness.

OBJECTIVE

We developed strategies to reduce incidence of severe ROP requiring laser surgery in premature infants.

METHODS

We studied 37 preterm infants who were born at a gestational age of <32 weeks, with a birth weight of <1500 g, receiving supplemental oxygen, and had been admitted to our neonatal intensive care unit. Infants received oxygen via mechanical ventilator, nasal continuous positive airway pressure (CPAP), or intranasal (I/N) and titration of oxygen was based on each infant's measured oxygen saturation (Spo(2)). For each infant, we monitored the Spo(2) trend, Spo(2) alarm limit, and the percentage of time that the alarm limit was set incorrectly. We implemented a Spo(2) targeting protocol and developed an algorithm for titrating fraction of inspired oxygen (Fio(2)).

RESULTS

After phase 1 of implementation, the percentage of time that Spo(2) readings were >95% was reduced to between 20% and 50%. However, our findings raised concern regarding the wide fluctuation of Spo(2) readings because of inconsistency in Fio(2) titration, which can contribute to deviation from the optimal target range. Accordingly, we developed an algorithm for titrating Fio(2) aimed at maintaining each infant's Spo(2) within the optimal target range. After phase 2 of implementation, the percentage of Spo(2) readings >95% was markedly reduced to between 0% and 15%. The incidence of infants with severe ROP requiring laser surgery decreased from 5 to 1.

CONCLUSIONS

A change in clinical practice aimed at maintaining oxygen within the target range to avoid a high Spo(2) was associated with a significant decrease in the incidence of both severe ROP and the need for laser surgery, thus reducing hospital costs and length of hospital stays for premature infants.

New guidelines for newborn resuscitation--a critical evaluation

The 2010 International Liaison Committee on Resuscitation guidelines for newborn resuscitation represent important progress. The criteria for assessment are simplified based on heart rate and respiration only and there is no timing of stages after the first 60 sec. Instead of giving supplemental oxygen, the guidelines state that 'it is best to start with air'. However, the optimal oxygen concentration later in the process and for premature babies is not yet clear. A description of an adequate heart rate response is not given, and the cut-off of 100 bpm may be arbitrary. There are still no clear recommendations regarding ventilation, inspiratory time, use of positive end expiratory pressure or continuous positive airway pressure. The guidelines do not mention which paCO2 level might be optimal. As colour pink assessment and routine suctioning of airways are not recommended anymore, there is an urgent need to obtain international consensus and create a new and revised Apgar score without these two variables.

CONCLUSION

In spite of improved guidelines for newborn resuscitation, there is still a number of unanswered questions and a need for more delivery room studies.

Erythropoietin attenuates hyperoxia-induced oxidative stress in the developing rat brain

Oxygen toxicity contributes to the pathogenesis of adverse neurological outcome in survivors of preterm birth in clinical studies. In infant rodent brains, hyperoxia triggers widespread apoptotic neurodegeneration, induces pro-inflammatory cytokines and inhibits growth factor signaling cascades. Since a tissue-protective effect has been observed for recombinant erythropoietin (rEpo), we hypothesized that rEpo would influence hyperoxia-induced oxidative stress in the developing rat brain. The aim of this study was to investigate the level of glutathione (reduced and oxidized), lipid peroxidation and the expression of heme oxygenase-1 (HO-1) and acetylcholinesterase (AChE) after hyperoxia and rEpo treatment. Six-day-old Wistar rats were exposed to 80% oxygen for 2-48 h and received 20,000 IU/kg rEpo intraperitoneally (i.p.). Sex-matched littermates kept under room air and injected with normal saline or rEpo served as controls. Treatment with rEpo significantly reduced hyperoxia-induced upregulation of oxidized glutathione (GSSG) and malondialdehyde, a product of lipid breakdown, whereas reduced glutathione (GSH) was upregulated by rEpo. In parallel, hyperoxia-treated immature rat brains revealed rEpo-suppressible upregulation of synaptic AChE-S as well as of the stress-inducible AChE-R variant, together predicting rEpo-protected cholinergic signaling and restrained inflammatory reactions. Furthermore, treatment with rEpo induced upregulation of HO-1 on mRNA, protein and activity level in the developing rat brain. Our results suggest that rEpo generates its protective effect against oxygen toxicity by a reduction of diverse oxidative stress parameters and by limiting the stressor-inducible changes in both HO-1 and cholinergic functions.

Lung protective ventilation strategies in paediatrics-A review

Ventilator Associated Lung Injury (VALI) is an iatrogenic phenomena that significantly impacts on the morbidity and mortality of critically ill patients. The hazards associated with mechanical ventilation are becoming increasingly understood courtesy of a large body of research. Barotrauma, volutrauma and biotrauma all play a role in VALI. Concomitant to this growth in understanding is the development of strategies to reduce the deleterious impact of mechanical ventilation. The majority of the research is based upon adult populations but with careful extrapolation this review will focus on paediatrics. This review article describes the physiological basis of VALI and discusses the various lung protective strategies that clinicians can employ to minimise its incidence and optimise outcomes for paediatric patients.

Is 100% oxygen necessary for the resuscitation of newborn infants?

This paper reproduces in detail the debate 'pro-and-con' regarding the use of 100% oxygen or room air in the resuscitation of the asphyxiated newly born infants, celebrated in Oslo at the 2002 European Association of Perinatal Medicine (EAPM) meeting, in which both co-authors participated as featured speakers. The authors describe their arguments which are based on medical tradition, clinical experience, basic science, and prospective randomized and pseudo-randomized clinical studies that have been reported in the past years. Both authors stress the importance of the long-term consequences of the use of high oxygen concentrations in the perinatal period and conclude that there is a need for further research in the way of ample prospective randomized clinical trials.

Effect of hyperoxia on serine phosphorylation of apoptotic proteins in mitochondrial membranes of the cerebral cortex of newborn piglets

Previous studies have shown that hyperoxia results in cerebral cortical neuronal apoptosis. Studies have also shown that phosphorylation of anti-apoptotic proteins Bcl-2 and Bcl-xl results in loss of their anti-apoptotic potential leading to alteration in mitochondrial membrane permeability and the release of apoptogenic proteins in the neuronal cell of the newborn piglets. The present study tests the hypothesis that cerebral hyperoxia will result in increased serine phosphorylation of apoptotic proteins Bcl-2, Bcl-xl, Bax, and Bad in the mitochondrial membranes of the cerebral cortex of newborn piglets. Twelve newborn piglets were divided into normoxic (Nx, n = 6) exposed to an FiO(2) of 0.21 for 1 h and hyperoxic (Hyx, n = 6) exposed to FiO(2) of 1.0 for 1 h. In the Hyx group, PaO(2) was maintained above 400 mmHg while the Nx group was kept at 80-100 mmHg. Cerebral cortical tissue was harvested and mitochondrial fractions were isolated. Mitochondrial membrane proteins were separated using 12% SDS-PAGE, and probed with anti-serine phosphorylated Bcl-2, Bcl-xl, Bax, and Bad antibodies. Protein bands were detected, analyzed by imaging densitometry and density expressed as absorbance (OD x mm(2)). Phosphorylated Bcl-2 (p-Bcl-2) protein density (OD x mm(2)) was 81.81 +/- 9.24 in Nx and 158.34 +/- 10.66 in Hyx (P < 0.05). Phosphorylated Bcl-xl (p-Bcl-xl) protein density was 52.98 +/- 3.59 in Nx and 99.62 +/- 18.22 in Hyx (P < 0.05). Phosphorylated Bax (p-Bax) protein was 161.13 +/- 6.27 in Nx and 174.21 +/- 15.95 in Hyx (P = NS). Phosphorylated Bad (p-Bad) protein was 166.24 +/- 9.47 in Nx 155.38 +/- 12.32 in Hyx (P = NS). The data show that there is a significant increase in serine phosphorylation of Bcl-2 and Bcl-xl proteins while phosphorylation of Bad and Bax proteins were not altered during hyperoxia in the mitochondrial fraction of the cerebral cortex of newborn piglets. We conclude that hyperoxia results in differential post-translational modification of anti-apoptotic proteins Bcl-2 and Bcl-xl as compared to pro-apoptotic proteins Bax and Bad in mitochondria. We speculate that phosphorylation of Bcl-2 and Bcl-xl will result in loss of their anti-apoptotic potential by preventing their dimerization with Bax leading to activation of the caspase cascade of neuronal death.

Oxigenoterapia inalatória em pacientes pediátricos internados em hospital universitário

OBJETIVO: Avaliar o uso da oxigenoterapia inalatória em crianças internadas em hospital universitário. MÉTODOS: Estudo prospectivo de crianças atendidas no Pronto-Socorro Pediátrico do Hospital das Clínicas da Faculdade de Medicina de Botucatu e que receberam oxigenoterapia durante a internação, de maio a setembro de 2005. Indicou-se oxigenoterapia se saturação de oxigênio inferior a 90% e frequência respiratória elevada para idade. Crianças em uso crônico de oxigênio ou com necessidade de ventilação mecânica foram excluídas. Foram avaliados: sintomas respiratórios, diagnósticos clínicos, saturação de oxigênio, método e tempo de oxigenoterapia e responsável pela prescrição. RESULTADOS: Foram atendidas 8.709 crianças no pronto-socorro, sendo que 2.769 (32%) apresentaram doenças respiratórias e 97 necessitaram de internação na enfermaria. Destas, 62 (64%) receberam oxigenoterapia. Das 62 crianças, 37 eram do sexo masculino e a idade variou de 2 meses a 14 anos (mediana: 8 meses). A causa de hipóxia foi pneumonia em 52 crianças (84%), asma em cinco, bronquiolite em quatro e traqueomalácia em uma. As prescrições de oxigenoterapia foram feitas por médicos, com monitoração de saturação de oxigênio por oxímetro de pulso. O tempo mediano de administração de O2 foi 6 dias e o cateter nasal foi usado em 94% dos casos, sendo raro o uso de máscaras ou capuz de oxigênio. CONCLUSÕES: A oxigenoterapia inalatória foi mais frequente em crianças com menor idade e em pacientes com pneumonia, sendo sua indicação compatível com critérios internacionais. O uso do cateter nasal mostrou-se seguro, simples, efetivo e de baixo custo.

Oxygen as a neonatal health hazard: call for détente in clinical practice

Education in oxygenation and in how oxygen is given to newborns needs to increase. Treatment with oxygen should no longer be considered proverbial and customary, regardless of our 'past experience' or consensus recommendations in clinical guidelines, since oxygen may lead to acute or chronic health effects.

CONCLUSION

Inappropriate oxygen use is a neonatal health hazard associated with aging, DNA damage and cancer, retinopathy of prematurity, injury to the developing brain, infection and others. Neonatal exposure to pure O2, even if brief, or to pulse oximetry >95% when breathing supplemental O2 must be avoided as much as possible.

Optimal oxygenation at birth and in the neonatal period

BACKGROUND

In recent years it has become clear that even a brief exposure to high oxygen concentration at birth and an oxygen saturation (SaO(2)) >93-95% in extremely low birth weight (ELBW) infants is more toxic than previously believed.

OBJECTIVE

To summarize and review clinical studies published to date either dealing with resuscitation of newborn infants with different oxygen concentrations or the use of high or low SaO(2) in the neonatal period of ELBW infants.

RESULTS

Three systematic reviews of five trials and seven individual studies including up to 2,011 newborn infants have shown that neonatal mortality is reduced by 30-40% if resuscitation is carried out with 21% instead of 100% O(2). Room air resuscitation also leads to faster early recovery and need for shorter duration of resuscitation. Six studies of ELBW infants have shown that retinopathy of prematurity and chronic lung disease are significantly reduced if SaO(2) is kept <93-95% compared with higher saturations. Avoidance of fluctuations in SaO(2) also seems to be important. Two observational studies suggest a significant 2.5- to 3.5-fold increased risk of childhood cancer in infants resuscitated with 100% O(2) for a few minutes.

CONCLUSIONS

To date there are sufficient data available to recommend that newborn resuscitation should not be carried out with 100% O(2). In ELBW infants, SaO(2) levels should be kept between 85 and 93% or possibly between 88 and 95%, but should definitely not exceed 95%. Fluctuations should be avoided.

Somatotropic axis derangement as an underlying factor in the genesis of retinopathy of prematurity

Recent research data suggest a significant role of prolonged low serum insulin-like growth factor (IGF)-I concentration in the genesis of retinopathy of prematurity (ROP). Evidence also reveals significant early postnatal nutritional deficits and growth deceleration among premature newborns.

CONCLUSION

Since serum IGF-I concentration is positively related to nutritional status, particularly protein nutrition, it would suggest that protein under-nutrition may be a major determinant of low serum IGF-I concentration and in the high risk of ROP.

Achieved versus intended pulse oximeter saturation in infants born less than 28 weeks' gestation: the AVIOx study

OBJECTIVE

The objective of this study was to document pulse oximeter saturation levels achieved in the first 4 weeks of life in infants who were born at < 28 weeks' gestation, compared with the levels that were targeted by local policy, and examine factors that are associated with compliance with the target range.

METHODS

Infants who were < 28 weeks' gestation and < or = 96 hours of age were enrolled in a prospective, multicenter cohort study. Oximetry data were collected with masked signal-extraction oximeters for a 72-hour period in each of the first 4 weeks of life. Data were compared with the pulse oximeter saturation target range prescribed by local institutional policy. Factors that were associated with intended range compliance were identified with hierarchical modeling.

RESULTS

Fourteen centers from 3 countries enrolled 84 infants with mean +/- SD birth weight of 863 +/- 208 g and gestational age of 26 +/- 1.4 weeks. Oxygen saturation policy limits ranged between 83% and 92% for lower limits and 92% and 98% for upper limits. For infants who received respiratory support, median pulse oximeter saturation level achieved was 95%. Center-specific medial levels were within the intended range at 12 centers. Centers maintained infants within their intended range 16% to 64% of the time but were above range 20% to 73% of the time. In hierarchical modeling, wider target ranges, higher target range upper limits, presence of a policy of setting oximeter alarms close to the target range limits, and lower gestational age were associated with improved target range compliance.

CONCLUSIONS

Success with maintaining the intended pulse oximeter saturation range varied substantially among centers, among patients within centers, and for individual patients over time. Most noncompliance was above the intended range. Methods for improving compliance and the effect of improved compliance on neonatal outcomes require additional research.

Pulse oximetry in very low birth weight infants: can oxygen saturation be maintained in the desired range?

OBJECTIVE

To determine if a change in the pulse oximeter goal range and high alarm limit for oxygen saturation (SpO2) alters the distribution of SpO2 for premature infants in oxygen.

STUDY DESIGN

This was a prospective, observational analysis. For group 1 (February 2002 to April 2002, n = 23), pulse oximeter alarms were set at 80% (low) and 96% (high), and the goal range was 90-95%. For group 2 (May 2002 to August 2003, n = 49), the high alarm was lowered to 94%, and the goal range was 88 to 94%. The SpO2 values for 24 h were downloaded from Nellcor pulse oximeters during the two periods and the percent time within, above and below the goal range was derived and compared.

RESULTS

Groups were similar except for use of post-natal steroids (group 2 > 1). The percent time within (57.7+/-9.8 vs 59.4+/-12.4%), above (15.4+/-10.6 vs 14+/-9.4%) and below (26.9+/-9.7 vs 26.6+/-10.2%) the goal range was similar for groups 1 and 2, respectively. However, the percent time with SpO2 <80% increased significantly for group 2 (4.0+/-2.7 vs 1.9+/-1.4%).

CONCLUSIONS

Changes in pulse oximeter policy and alarms in labile, sick premature infants need evaluation for their effects on the distribution of SpO2 values before routine use.

Childhood cancer following neonatal oxygen supplementation

OBJECTIVE

To evaluate the relationship between neonatal oxygen supplementation (O2) and childhood cancer in the Collaborative Perinatal Project (CPP).

STUDY DESIGN

The CPP consisted of 54,795 children born between 1959 and 1966 and followed to age 8 years. We used Cox proportional hazards modeling to examine the association between history of neonatal O2 and cancer (n = 48).

RESULTS

The hazard ratio (HR) for any O2 was 1.77 (95% confidence interval [CI] = 0.94 to 3.35). The HR for continuous duration of O2 was near 1 and not significant. However, the HRs were 0.69 (95% CI = 0.17 to 2.88) and 2.87 (95% CI = 1.46 to 5.66) when comparing 0 to 2 and 3 or more minutes of O2, respectively, to no O2. The latter association was weaker (HR = 2.00; 95% CI = 0.88 to 4.54) and not significant ( P = .10) when analysis was restricted to cancers diagnosed after age 1 year (n = 41).

CONCLUSIONS

These findings are consistent with an association between O 2 for 3 minutes or longer and cancer in childhood, and should serve as a basis for further study.

Restoration of cardiopulmonary function with 21% versus 100% oxygen after hypoxaemia in newborn pigs

OBJECTIVE

To assess the consequences of hypoxaemia and resuscitation with room air versus 100% O(2) on cardiac troponin I (cTnI), cardiac output (CO), and pulmonary artery pressure (PAP) in newborn pigs.

DESIGN

Twenty anaesthetised pigs (12-36 hours; 1.7-2.7 kg) were subjected to hypoxaemia by ventilation with 8% O(2). When mean arterial blood pressure fell to 15 mm Hg, or arterial base excess was < or = -20 mmol/l, resuscitation was performed with 21% (n = 10) or 100% (n = 10) O(2) for 30 minutes, then ventilation with 21% O(2) for 120 minutes. Blood was analysed for cTnI. Ultrasound examinations of CO and PAP (estimated from tricuspid regurgitation velocity (TR-Vmax)) were performed at baseline, during hypoxia, and at the start of and during reoxygenation.

RESULTS

cTnI increased from baseline to the end point (p<0.001), confirming a serious myocardial injury, with no differences between the 21% and 100% O(2) group (p = 0.12). TR-Vmax increased during the insult and returned towards baseline values during reoxygenation, with no differences between the groups (p = 0.11) or between cTnI concentrations (p = 0.31). An inverse relation was found between increasing age and TR-Vmax during hypoxaemia (p = 0.034). CO per kg body weight increased during the early phase of hypoxaemia (p<0.001), then decreased. Changes in CO per kg were mainly due to changes in heart rate, with no differences between the groups during reoxygenation (p = 0.298).

CONCLUSION

Hypoxaemia affects the myocardium and PAP. During this limited period of observation, reoxygenation with 100% O(2) showed no benefits compared with 21% O(2) in normalising myocardial function and PAP. The important issue may be resuscitation and reoxygenation without hyperoxygenation.

Caspase-1-processed interleukins in hyperoxia-induced cell death in the developing brain

Infants born prematurely may develop neurocognitive deficits without an obvious cause. Oxygen, which is widely used in neonatal medicine, constitutes one possible contributing neurotoxic factor, because it can trigger neuronal apoptosis in the developing brain of rodents. We hypothesized that two caspase-1-processed cytokines, interleukin (IL)-1beta and IL-18, are involved in oxygen-induced neuronal cell death. Six-day-old Wistar rats or C57/BL6 mice were exposed to 80% oxygen for various time periods (2, 6, 12, 24, and 48 hours). Neuronal cell death in the brain, as assessed by Fluoro-Jade B and silver staining, peaked at 12 to 24 hours and was preceded by a marked increase in mRNA and protein levels of caspase 1, IL-1beta, IL-18, and IL-18 receptor alpha (IL-18Ralpha). Intraperitoneal injection of recombinant human IL-18-binding protein, a specific inhibitor of IL-18, attenuated hyperoxic brain injury. Mice deficient in IL-1 receptor-associated kinase 4 (IRAK-4), which is pivotal for both IL-1beta and IL-18 signal transduction, were protected against oxygen-mediated neurotoxicity. These findings causally link IL-1beta and IL-18 to hyperoxia-induced cell death in the immature brain. These cytokines might serve as useful targets for therapeutic approaches aimed at preserving neuronal function in the immature brain, which is exquisitely sensitive to a variety of iatrogenic measures including oxygen.

Resuscitation of newborn infants with 100% oxygen or air: a systematic review and meta-analysis

BACKGROUND

International consensus statements for resuscitation of newborn infants recommend provision of 100% oxygen with positive pressure if assisted ventilation is required. However, 100% oxygen exacerbates reperfusion injury in animals and reduces cerebral perfusion in newborn babies. We aimed to establish whether resuscitation with air decreased mortality or neurological disability in newborn infants compared with 100% oxygen.

METHODS

We did a systematic review and meta-analysis of trials that compared resuscitation with air versus 100% oxygen, using the methods of the Cochrane Collaboration. We combined data for similar outcomes in the analysis where appropriate, using a fixed-effects model.

FINDINGS

Five trials (two masked and three unmasked), consisting of 1302 newborn infants, fulfilled the inclusion criteria. Most babies were born at or near term in developing countries. In the three unmasked studies, infants resuscitated with room air who remained cyanotic and bradycardic were switched to 100% oxygen at 90 s. The masked studies allowed crossover to the other gas during the first minutes of life. Although no individual trial showed a difference in mortality, the pooled analysis showed a significant benefit for infants resuscitated with air (relative risk 0.71 [95% CI 0.54 to 0.94], risk difference -0.05 [-0.08 to -0.01]). The effect on long-term development could not be reliably determined because of methodological limitations in the one study that followed up infants beyond 12 months of age.

INTERPRETATION

For term and near-term infants, we can reasonably conclude that air should be used initially, with oxygen as backup if initial resuscitation fails. The effect of intermediate concentrations of oxygen at resuscitation needs to be investigated. Future trials should include and stratify for premature infants.

The role of oxygen in neonatal resuscitation

New knowledge has accumulated in recent years making it prudent to ask questions regarding current oxygenation policies and guidelines. Because new-born resuscitation affects so many individuals, and because resuscitation procedures may have dramatic consequences on infant and child health, intensified discussion and research in this field are not only necessary but are a requirement. In particular, there is a lack of data on infants born before term. It is difficult to give absolute recommendations on which oxygen concentration should be applied for newborn resuscitation; however, it seems that ambient air is safe. It is easy to handle, is always at hand, and is inexpensive. Conversely, regarding 100% O2, I believe we have sufficient data to conclude that this should not be given routinely at birth to depressed infants; however, whether it is beneficial or harmful to start out resuscitation with 30%, 40%, or 60% O2 is not known. No data exist to answer this question. A call for more research in this area is timely. The effect of pure oxygen on cell growth and cell death, gene activation, and possibly DNA damage should be carefully investigated. Even before such data are collected, it is known that pure oxygen at birth triggers long-term and poorly understood effects. Oxygen obviously is more toxic than previously thought, and oxygen given to small infants has a 50-year history of uncertain benefits. Table 1 summarizes the pros and cons of using 21%versus 100% 02 for newborn resuscitation. Brain circulation as assessed by microspheres is restored as quickly with 21% O2 as it is with 100% O2; however, microcirculation is somewhat slower. Metabolism, pulmonary flow, and myocardial performance are normalized just as quickly by 21% and 100% O2. Brain injury as assessed by glycerol augmentation, matrix injury, and neonatal mortality is less in infants given 21% versus 100% O2.

The effect of chronic or intermittent hypoxia on cognition in childhood: a review of the evidence

OBJECTIVE

A review of the evidence concerning the effect of chronic or intermittent hypoxia on cognition in childhood was performed by using both a systematic review of the literature and critical appraisal criteria of causality. Because of the significant impact of behavioral disorders such as attention-deficit/hyperactivity disorder on certain cognitive functions as well as academic achievement, the review also included articles that addressed behavioral outcomes.

METHODS

Both direct and indirect evidence were collected. A structured Medline search was conducted from the years 1966-2000 by using the OVID interface. Both English- and non-English-language citations were included. Significant articles identified by the reviewers up to 2003 were also included. To be included as direct evidence, an article needed to be an original report in a peer-reviewed journal with data on cognitive, behavioral, or academic outcomes in children up to 14 years old, with clinical conditions likely to be associated with exposure to chronic or intermittent hypoxia. Indirect evidence from other reviews and publications in closely related fields, including experimental studies in adults, was used to help formulate conclusions. Two reviewers screened abstracts and titles. Each article included as direct evidence received a structured evaluation by 2 reviewers. Adjudication of differences was performed by a group of 2 reviewers and a research consultant. After this review, tables of evidence were constructed that were used as the basis for group discussion and consensus development. Indirect evidence assigned by topic to specific reviewers was also presented as part of this process. A formal procedure was used to rank the studies by design strength. The critical appraisal criteria for causation described in Evidence Based Pediatrics and Child Health (Moyer V, Elliott E, Davis R, et al, eds. London, United Kingdom: BMJ Books; 2000:46-55) were used to develop consensus on causality.

RESULTS

A total of 788 literature citations were screened. For the final analysis, 55 articles met the criteria for inclusion in the direct evidence. Of these, 43 (78.2%) reported an adverse effect. Of the 37 controlled studies, 31 (83.8%) reported an adverse effect. Adverse effects were noted at every level of arterial oxygen saturation and for exposure at every age level except for premature newborns. The studies were classified into 5 clinical categories: congenital heart disease (CHD), sleep-disordered breathing (SDB), asthma, chronic ventilatory impairment, and respiratory instability in infants. Two of these categories, CHD and SDB, which accounted for 42 (76.4%) of the included articles, fulfilled the Evidence Based Pediatrics and Child Health criteria for causation. The indirect evidence included 8 reviews, 1 meta-analysis, and 10 original reports covering the fields of adult anoxia, animal research, SDB in adults, natural and experimental high-altitude studies, perinatal hypoxic-ischemic encephalopathy, anemia, and carbon-monoxide poisoning. The studies of high-altitude and carbon-monoxide poisoning provided evidence for causality.

CONCLUSIONS

Adverse impacts of chronic or intermittent hypoxia on development, behavior, and academic achievement have been reported in many well-designed and controlled studies in children with CHD and SDB as well as in a variety of experimental studies in adults. This should be taken into account in any situation that may expose children to hypoxia. Because adverse effects have been noted at even mild levels of oxygen desaturation, future research should include precisely defined data on exposure to all levels of desaturation.

Increased myocardial matrix metalloproteinases in hypoxic newborn pigs during resuscitation: effects of oxygen and carbon dioxide

BACKGROUND

Perinatal asphyxia is associated with cardiac dysfunction, and it is important to prevent further tissue injury during resuscitation. There is increasing evidence that myocardial matrix metalloproteinases (MMPs) are involved in myocardial hypoxaemia-reoxygenation injury.

OBJECTIVE

To assess MMPs and antioxidant capacity in newborn pigs after global ischaemia and subsequent resuscitation with ambient air or 100% O(2) at different PaCO(2)-levels.

METHODS

Newborn pigs (12-36 h of age) were resuscitated for 30 min by ventilation with 21% or 100% O(2) at different PaCO(2) levels after a hypoxic insult, and thereafter observed for 150 min. In myocardial tissue extracts, MMPs were analyzed by gelatin zymography and broad matrix-degrading capacity (total MMP). Total endogenous antioxidant capacity in myocardial tissue extracts was measured by the oxygen radical absorbance capacity (ORAC) assay.

RESULTS

Matrix metalloproteinase-2 more than doubled from baseline values (P < 0.001), and was higher in piglets resuscitated with 100% O(2) than with ambient air (P = 0.012). The ORAC value was considerably decreased (P < 0.001). In piglets with elevated PaCO(2), total MMP-activity in the right ventricle was more increased than in the left ventricle (P = 0.008). In the left ventricle, total MMPactivity was higher in the piglets with low PaCO(2) than in the piglets with elevated PaCO(2) (P = 0.013).

CONCLUSION

In hypoxaemia-reoxygenation injury the MMP-2 level was highly increased and was most elevated in the piglets resuscitated with 100% O(2). Antioxidant capacity was considerably decreased. Assessed by total MMP-activity, elevated PaCO(2) during resuscitation might protect the left ventricle, and probably increase right ventricle injury of the myocardium.

Effects on the fetus and newborn of maternal analgesia and anesthesia: a review

PURPOSE

To review the effects of maternal anesthesia and analgesia on the fetus and newborn.

METHODS

An on-line computerized search of Medline, Embase, and the Cochrane Collaboration via PubMed was conducted. English language articles were selected. The bibliographies of relevant articles and additional material from other published sources were retrieved and reviewed.

PRINCIPAL FINDINGS

No one test clearly separates the effects on the fetus/newborn, if any, of maternally administered medication during labour and delivery, or during surgery for non-obstetric indications. Supposition in this regard is limited in part by methodology previously used to study the transplacental passage of various drugs. This work needs to be repeated using a human model. Routine maternal supplemental oxygen administration is being questioned in light of research showing that free radical generation and oxidative stress are implicated as the underlying mechanisms in several neonatal conditions. Maternal hypotension is associated with neonatal acidemia and base excess correlates with neonatal outcome. Common postpartum analgesics transfer minimally into breast milk. Maternal or fetal surgery conducted during pregnancy necessitates modification of both anesthetic and surgical approaches. The key to resuscitation of the fetus is resuscitation of the mother: intra-uterine maneuvers, including perimortem Cesarean section, aim to reverse treatable causes of fetal asphyxia, restore fetal oxygenation, and correct fetal acidosis.

CONCLUSIONS

The well-being of the infant is a major criterion for evaluating the anesthetic management of pregnant women. Many tools exist to assist with this determination for the fetus, whereas few are available to evaluate the newborn.

Resuscitation with 100% O(2) does not protect the myocardium in hypoxic newborn piglets

BACKGROUND

Perinatal asphyxia is associated with cardiac dysfunction secondary to myocardial ischaemia. Cardiac troponin I (cTnI) is a marker of myocardial necrosis. Raised concentrations in the blood are related to perinatal asphyxia and increased morbidity.

OBJECTIVE

To assess porcine myocardial damage from enzyme release during hypoxaemia induced global ischaemia, and subsequent resuscitation with ambient air or 100% O(2). To investigate whether CO(2) level during resuscitation influences myocardial damage.

DESIGN

Newborn piglets (12-36 hours) were exposed to hypoxaemia by ventilation with 8% O(2) in nitrogen. When mean arterial blood pressure had fallen to 15 mm Hg, or base excess to < -20 mmol/l, the animals were randomly resuscitated by ventilation with either 21% O(2) (group A, n = 29) or 100% O(2) (group B, n = 29) for 30 minutes. Afterwards they were observed in ambient air for another 150 minutes. During resuscitation, the two groups were further divided into three subgroups with different CO(2) levels.

ANALYSIS

Blood samples were analysed for cTnI, myoglobin, and creatine kinase-myocardial band (CK-MB) at baseline and at the end of the study.

RESULTS

cTnI increased more than 10-fold (p < 0.001) in all the groups. Myoglobin and CK-MB doubled in concentration.

CONCLUSION

The considerable increase in cTnI indicates seriously affected myocardium. Reoxygenation with 100% oxygen offered no biochemical benefit over ambient air. CK-MB and myoglobin were not reliable markers of myocardial damage. Normoventilation tended to produce better myocardial outcome than hyperventilation or hypoventilation.