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

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.

Band 3 protein function and oxidative stress in erythrocytes

Band 3 protein (B3p), anion transporter, allows the HCO₃ ^- /Cl^- exchange across plasma membrane and plays an important role for erythrocytes homeostasis. In addition, B3p is linked to proteins cytoskeleton, thus contributing to cell shape and deformability, essential to erythrocytes adjustment within narrowest capillaries. Taking into account that erythrocytes are a suitable cell model to investigate the response of the oxidative stress effects, B3p functions, and specifically anion exchange capability, determining the rate constant for SO₄ ^2- uptake, has been considered. As, in the latter years, rising attention has been addressed to membrane transport system, and particularly to this protein, the present mini-review has been conceived to report the most recent knowledge about B3p, with specific regard to its functions in oxidative stress conditions, including oxidative stress-related diseases.

Hyperoxygenation With Cardiopulmonary Resuscitation and Targeted Temperature Management Improves Post-Cardiac Arrest Outcomes in Rats

Background Oxygen plays a pivotal role in cardiopulmonary resuscitation (CPR) and postresuscitation intervention for cardiac arrest. However, the optimal method to reoxygenate patients has not been determined. This study investigated the effect of timing of hyperoxygenation on neurological outcomes in cardiac arrest/CPR rats treated with targeted temperature management. Methods and Results After induction of ventricular fibrillation, male Sprague-Dawley rats were randomized into 4 groups (n=16/group): (1) normoxic control; (2) O₂_CPR, ventilated with 100% O₂ during CPR; (3) O₂_CPR+postresuscitation, ventilated with 100% O₂ during CPR and the first 3 hours of postresuscitation; and (4) O₂_postresuscitation, ventilated with 100% O₂ during the first 3 hours of postresuscitation. Targeted temperature management was induced immediately after resuscitation and maintained for 3 hours in all animals. Postresuscitation hemodynamics, neurological recovery, and pathological analysis were assessed. Brain tissues of additional rats undergoing the same experimental procedure were harvested for ELISA-based quantification assays of oxidative stress-related biomarkers and compared with the sham-operated rats (n=6/group). We found that postresuscitation mean arterial pressure and quantitative electroencephalogram activity were significantly increased, whereas astroglial protein S100B, degenerated neurons, oxidative stress-related biomarkers, and neurologic deficit scores were significantly reduced in the O₂_CPR+postresuscitation group compared with the normoxic control group. In addition, 96-hour survival rates were significantly improved in all of the hyperoxygenation groups. Conclusions In this cardiac arrest/CPR rat model, hyperoxygenation coupled with targeted temperature management attenuates ischemia/reperfusion-induced injuries and improves survival rates. The beneficial effects of high-concentration oxygen are timing and duration dependent. Hyperoxygenation commenced with CPR, which improves outcomes when administered during hypothermia.

Chest Compression in Neonatal Cardiac Arrest: Cerebral Blood Flow Measurements in Experimental Models

The main aim of this paper was to provide an overview of studies that measured cerebral blood flow (CBF), directly or indirectly, during chest compression (CC) in neonatal animals. Our main research question was: how did different ways of performing CC influence CBF. We also aimed to discuss strengths and limitations of different methods for measuring CBF. Based on a search in Medline Ovid, we identified three studies in piglets that investigated different CC:ventilation (C:V) ratios, as well as three piglet studies investigating continuous CC with asynchronous ventilation. CBF was measured indirectly in all studies by means of carotid artery (CA) flow and regional cerebral oxygenation (rcSO₂). The CA provides flow to the brain, but also to extracerebral structures. The relative sizes of the internal and external carotid arteries and their flow distributions are species-dependent. rcSO₂ is a non-invasive continuous measure, but does not only reflect CBF, but also cerebral blood volume and the metabolic rate of oxygen in the brain. Continuous CC with asynchronous ventilation at a CC rate of 120/min, and combining CC with a sustained inflation (four studies in piglets and one in lambs) provided a faster CBF recovery compared with the standard 3:1 C:V approach.

Effects of the duration of postresuscitation hyperoxic ventilation on neurological outcome and survival in an asphyxial cardiac arrest rat model

Cardiac arrest leads to sudden cessation of oxygen supply and cerebral hypoxia occurs when there is not sufficient oxygen supplied to the brain. Current Guidelines for adult cardiopulmonary resuscitation (CPR) and emergency cardiovascular care recommend the use of 100% oxygen during resuscitative efforts to maximize the probability of achieving the return of spontaneous circulation (ROSC). However, the optimal strategy for oxygen management after ROSC is still debatable. The aim of the present study was to evaluate the effects of the duration of post-resuscitation hyperoxic ventilation on neurological outcomes in asphyxial cardiac arrest rats treated with targeted temperature management (TTM). Asphyxia was induced by blocking the endotracheal tube in 80 adult male Sprague-Dawley rats. CPR begun after 7 min of untreated cardiac arrest. Animals were randomized to either the normoxic control under normothermia (NNC) group or to one of the 4 experimental groups (n = 16 each) immediately after ROSC: ventilated with 100% oxygen for 0 (O₂_0h), 1 (O₂_1h), 3 (O₂_3h), or 5 (O₂_5h) h and ventilated with room air thereafter under TTM. Physiological variables were recorded at baseline and during the 6 h postresuscitation monitoring period. Animals were closely observed for 96 h to assess neurologic recovery and survival. There were no significant differences in baseline measurements between groups, and all animals were successfully resuscitated. There were significant interactions between the duration of 100% oxygen administration and hemodynamics as well as, myocardial and cerebral injuries. Among all the durations of hyperoxic ventilation investigated, significantly lower neurological deficit scores and higher survival rates were observed in the O₂_3h group than in the NNC group. In conclusion, postresuscitation hyperoxic ventilation leads to improved PaO₂, PaCO₂, hemodynamic, myocardial and cerebral recovery in asphyxial cardiac arrest rats treated with TTM. However, the beneficial effects of high concentration-oxygen are duration dependent and ventilation with 100% oxygen during induced hypothermia contributes to improved neurological recovery and survival after 96 h.

Is Supplemental Oxygen Needed in Cardiac Compression?-The Influence of Oxygen on Cerebral Perfusion in Severely Asphyxiated Neonates With Bradycardia or Cardiac Asystole

Background: Previous studies have investigated hemodynamic recovery using 21% vs. 100% oxygen during cardiopulmonary resuscitation (CPR) with chest compression (CC) in term infants. Animal studies indicate that systemic circulatory recovery is the same whether 21 or 100% oxygen is used during neonatal CPR. One of the main goals of resuscitation is to maintain cerebral oxygen delivery and prevent cerebral hypo- and hyperoxygenation. Oxygen delivery to the brain depends on cerebral hemodynamics, concentration of inhaled oxygen and blood oxygen content. The aim of this paper was to synthesize available research about cerebral oxygen delivery during CPR using different oxygen concentrations. Our research questions included how do different oxygen concentrations during CPR with CC influence cerebral perfusion and oxygen delivery, and how do cerebral hemodynamics during CC influence outcomes. Methods: A search in Medline Ovid using the search terms hypoxia AND oxygen AND cerebrovascular circulation AND infant, newborn. Inclusion criteria included studies of hypoxia and resuscitation of term infants. Studies were excluded if no measures of cerebral blood flow (CBF), oxygenation, or perfusion were reported. Results: The search retrieved 21 papers. None of the studies directly fulfilled our inclusion criteria. The reference lists of some of the retrieved papers provided relevant animal studies with slightly conflicting results regarding blood flow and oxygen delivery to the brain using 21 or 100% oxygen. No study in term infants was identified, but we included one study in preterm infants. Studies in asphyxiated animals indicate that 100% oxygen increases CBF and oxygenation during and after CC with a potential increase in oxidative stress. Conclusion: In asphyxia, cerebral autoregulation may be impaired. Pure oxygen administration during CC may result in cerebral hyperperfusion and increased cerebral oxygen delivery, which may be associated with oxidative stress-related damage to the brain tissue. As systemic circulatory recovery is the same whether 21 or 100% oxygen is used during neonatal CPR, it is important to investigate whether brain damage could be aggravated when 100% oxygen is used.

Ventilation strategies for preventing oxidative stress-induced injury in preterm infants with respiratory disease: an update

Reactive oxygen and nitrogen species are produced by several inflammatory and structural cells of the airways. The lungs of preterm newborns are susceptible to oxidative injury induced by both reactive oxygen and nitrogen species. Increased oxidative stress and imbalance in antioxidant enzymes may play a role in the pathogenesis of inflammatory pulmonary diseases. Preterm infants are frequently exposed to high oxygen concentrations, infections or inflammation; they have reduced antioxidant defense and high free iron levels which enhance toxic radical generation. Multiple ventilation strategies have been studied to reduce injury and improve outcomes in preterm infants. Using lung protective strategies, there is the need to reach a compromise between satisfaction of gas exchange and potential toxicities related to over-distension, derecruitment of lung units and high oxygen concentrations. In this review, the authors summarize scientific evidence concerning oxidative stress as it relates to resuscitation in the delivery room and to the strategies of ventilation.

Changes in amplitude-integrated electroencephalograms in piglets during selective mild head cooling after hypoxia-ischemia

BACKGROUND

Amplitude-integrated electroencephalogram (aEEG) is a simplified, alternative means of monitoring cerebral function and may be more useful clinically in some situations than conventional EEG. The aim of this study is to evaluate newborn piglets as an animal model to examine the effect of selective mild head cooling (HC) on aEEG after hypoxia-ischemia (HI).

METHODS

Thirty-four piglets were randomly allocated to the following treatment groups: normothermic control group (NC, n = 7), selective HC control group (HC, n = 9), normothermic HI group (NHI, n = 9), and selective HC HI group (SHC-HI, n = 9). HI was induced by temporary occlusion of both carotid arteries and simultaneous reduction of the concentration of inspired oxygen to 6% for 30 minutes. Mild hypothermia (35°C) was induced after HI using a HC cap and was maintained for 24 hours. Changes in aEEG were monitored for 6 days after these treatments and the incidence of abnormalities analyzed. Physiological parameters were also measured during this period.

RESULTS

In the two HI groups, animals exhibited severely abnormal aEEGs [continuous low voltage (CLV), burst-suppression, or flat tracing (FT)] 20 minutes after the beginning of HI. At 2 hours, the aEEG returned to normal in most of these animals. From 12 hours to 6 days, all animals in the NHI group exhibited severely abnormal aEEGs. Fewer animals in the SHC-HI group exhibited severe abnormal aEEGs during this time period, and four out of nine (44.4%) animals had continuous normal voltage (CNV) at 6 days.

CONCLUSIONS

Selective mild HC decreases the incidence of severe abnormal aEEGs at late times after HI in newborn piglets.

Implementation of a titrated oxygen protocol in the out-of-hospital setting

Oxygen is one of the most frequently-used therapeutic agents in medicine and the most commonly administered drug by prehospital personnel. There is increasing evidence of harm with too much supplemental oxygen in certain conditions, including stroke, chronic obstructive pulmonary disease (COPD), neonatal resuscitations, and in postresuscitation care. Recent guidelines published by the British Thoracic Society (BTS) advocate titrated oxygen therapy, but these guidelines have not been widely adapted in the out-of-hospital setting where high-flow oxygen is the standard. This report is a description of the implementation of a titrated oxygen protocol in a large urban-suburban Emergency Medical Services (EMS) system and a discussion of the practical application of this out-of-hospital protocol.

Reoxygenation of asphyxiated newborn piglets: administration of 100% oxygen causes significantly higher apoptosis in cortical neurons, as compared to 21%

OBJECTIVE

Evaluation of neuronal changes in an animal experimental model of normocapnic hypoxia- reoxygenation.

MATERIALS AND METHODS

Fifty male piglets were the study subjects; normocapnic hypoxia was induced in 40 piglets and ten were sham-operated (controls). When bradycardia and/or severe hypotension occurred, reoxygenation was initiated. Animals were allocated in 4 groups according to the oxygen concentration, they were resuscitated with 18%, 21%, 40%, and 100% O2. Persisting asystole despite 10 minutes of cardiopulmonary resuscitation and return of spontaneous circulation were the endpoints of the experiment. Surviving animals were euthanized and brain cortex samples were collected, hematoxylin and eosin-stained, and examined for apoptotic bodies observing 10 consecutive high power fields.

RESULTS

Histological examination of the control group did not show any pathological change. On the contrary, apoptosis of neurons was found in 87.5% of treated animals. When specimens were examined according to the oxygen concentration used for resuscitation, we found marked intergroup variability; a higher percentage of apoptotic neurons was observed in piglets of group 4 (100% oxygen) compared to the others (P=0.001).

CONCLUSIONS

This preliminary data shows that normocapnic hypoxia and reoxygenation in Landrace/Large White piglets resulted in significant histological changes in the brain cortex. The degree of pathological changes in cortical neurons was significantly associated with the oxygen concentration used for reoxygenation, with a higher percentage of apoptotic neurons being observed in piglets reoxygenated with 100% compared to 18% O2 and to 21% O2.

Hypoxic-preconditioning enhances the regenerative capacity of neural stem/progenitors in subventricular zone of newborn piglet brain

Perinatal hypoxia-ischemia (HI) results in brain injury, whereas mild hypoxic episodes result in preconditioning, which can significantly reduce the vulnerability of the brain to subsequent severe hypoxia-ischemia. Hypoxic-preconditioning (PC) has been shown to enhance cell survival and differentiation of progenitor cells in the central nervous system (CNS). The purpose of this study was to determine whether pretreatment with PC prior to HI stimulates subventricular zone (SVZ) proliferation and neurogenesis in newborn piglets. One-day-old piglets were subjected to PC (8% O2/92% N2) for 3h and 24h later were exposed to HI produced by combination of hypoxia (5% FiO2) for a pre-defined period of 30min and ischemia induced by a period of 10min of hypotension. Here we demonstrate that SVZ derived neural stem/progenitor cells (NSPs) from PC, HI and PC+HI piglets proliferated as neurospheres, expressed neural progenitor and neurodevelopmental markers, and that greater proportion of the spheres generated are multipotential. Neurosphere assay revealed that preconditioning pretreatment increased the number of NSP-derived neurospheres in SVZ following HI compared to normoxic and HI controls. NSPs from preconditioned SVZ generated twice as many neurons and astrocytes in vitro. Injections with 5-Bromo-2-deoxyuridine (BrdU) after PC revealed a robust proliferative response within the SVZ that continued for one week. PC also increased neurogenesis in vivo, doublecortin positive cells with migratory profiles were observed streaming from the SVZ to striatum and neocortex. These findings show that the induction of proliferation and neurogenesis by PC might be a positive adaptation for an efficient repair and plasticity in the event of a hypoxic-ischemic insult.

Oxygen administration for the resuscitation of term and preterm infants

Oxygen has been widely used in neonatal resuscitation for about 300 years. In October 2010, the International Liaison Committee on Neonatal Resuscitation released new guidelines. Based on experimental studies and randomized clinical trials, the recommendations on evaluation and monitoring of oxygenation status and oxygen supplementation in the delivery room were revised in detail. They include: inaccuracy of oxygenation clinical assessment (colour), mandatory use of pulse oximeter, specific saturation targets and oxygen concentrations during positive pressure ventilation in preterm and term infants. In this review, we describe oxygen management in the delivery room in terms of clinical assessment, monitoring, treatment and the gap of knowledge.

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.

Cellular biology of end organ injury and strategies for prevention of injury

The interruption of placental blood flow induces circulatory responses to maintain cerebral, cardiac, and adrenal blood flow with reduced renal, hepatic, intestinal, and skin blood flow. If placental compromise is prolonged and/or severe, total circulatory failure is likely with cerebral hypoperfusion and resultant hypoxic ischemic cerebral injury with collateral renal, cardiac, and hepatic injury. Management strategies should be targeted at restoring cerebral perfusion and oxygen delivery and minimizing the extent of secondary injury. Specifically, the focus should include the judicious use of supplemental oxygen, avoidance of hypoglycemia and elevated temperature in the delivery room, and the early administration of therapeutic hypothermia to high-risk infants.

Neonatal resuscitation: in pursuit of evidence gaps in knowledge

Guidelines for the techniques of resuscitating newly born infants have undergone major revisions over the past 25 years. The International Liaison Committee on Resuscitation (ILCOR) is committed to "periodically developing and publishing a consensus on resuscitation science" every five years with the most recent Consensus on Science and Treatment Recommendations (CoSTR) statement published in 2010. The CoSTR document is used as a basis for developing specific resuscitation guidelines felt to be appropriate for implementation in respective countries. A "gaps in knowledge" summary is created at the conclusion of a cycle. It is a goal that identification of these knowledge gaps will stimulate investigators to pursue more targeted studies to help close the gaps. The current document is based on the "gaps in knowledge" summary for neonatal resuscitation that was created at the conclusion of the 2005-2010 ILCOR cycle.

Normoxic versus hyperoxic resuscitation in pediatric asphyxial cardiac arrest: effects on oxidative stress

OBJECTIVE

To determine the effects of normoxic vs. hyperoxic resuscitation on oxidative stress in a model of pediatric asphyxial cardiac arrest.

DESIGN

Prospective, interventional study.

SETTING

University research laboratory.

SUBJECTS

Postnatal day 16-18 rats (n = 5 per group).

INTERVENTIONS

Rats underwent asphyxial cardiac arrest for 9 min. Rats were randomized to receive 100% oxygen, room air, or 100% oxygen with polynitroxyl albumin (10 mL·kg⁻¹ intravenously, 0 and 30 min after resuscitation) for 1 hr from the start of cardiopulmonary resuscitation. Shams recovered in 100% oxygen or room air after surgery.

MEASUREMENTS AND MAIN RESULTS

Physiological variables were recorded at baseline to 1 hr after resuscitation. At 6 hrs after asphyxial cardiac arrest, levels of reduced glutathione and protein-thiols (fluorescent assay), activities of total superoxide dismutase and mitochondrial manganese superoxide dismutase (cytochrome c reduction method), manganese superoxide dismutase expression (Western blot), and lipid peroxidation (4-hydroxynonenal Michael adducts) were evaluated in brain tissue homogenates. Hippocampal 3-nitrotyrosine levels were determined by immunohistochemistry 72 hrs after asphyxial cardiac arrest. Survival did not differ among groups. At 1 hr after resuscitation, Pao2, pH, and mean arterial pressure were decreased in room air vs. 100% oxygen rats (59 ± 3 vs. 465 ± 46 mm Hg, 7.36 ± 0.05 vs. 7.42 ± 0.03, 35 ± 4 vs. 45 ± 5 mm Hg; p < .05). Rats resuscitated with 100% oxygen had decreased hippocampal reduced glutathione levels vs. sham (15.3 ± 0.4 vs. 20.9 ± 4.1 nmol·mg protein⁻¹; p < .01). Hippocampal manganese superoxide dismutase activity was significantly increased in 100% oxygen rats vs. sham (14 ± 2.4 vs. 9.5 ± 1.6 units·mg protein⁻¹, p < .01), with no difference in protein expression of manganese superoxide dismutase. Room air and 100% oxygen plus polynitroxyl albumin groups had hippocampal reduced glutathione and manganese superoxide dismutase activity levels comparable with sham. Protein thiol levels were unchanged across groups. Compared with all other groups, rats receiving 100% oxygen had increased immunopositivity for 3-nitrotyrosine in the hippocampus and increased lipid peroxidation in the cortex.

CONCLUSIONS

Resuscitation with 100% oxygen leads to increased oxidative stress in a model that mimics pediatric cardiac arrest. This may be prevented by using room air or giving an antioxidant with 100% oxygen resuscitation.

Neonatal resuscitation: Current issues

The following guidelines are intended for practitioners responsible for resuscitating neonates. They apply primarily to neonates undergoing transition from intrauterine to extrauterine life. The updated guidelines on Neonatal Resuscitation have assimilated the latest evidence in neonatal resuscitation. Important changes with regard to the old guidelines and recommendations for daily practice are provided. Current controversial issues concerning neonatal resuscitation are reviewed and argued in the context of the ILCOR 2005 consensus.

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.

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.

Refining the role of oxygen administration during delivery room resuscitation: what are the future goals?

Oxygen was discovered more than 200 years ago and was thought to be both essential and beneficial for all animal life. Although it is now over 100 years since oxygen was first shown to damage biological tissues exposed to high concentrations, and more than 50 years since it was implicated in the aetiology of retinopathy of prematurity, the use of 100% oxygen was still recommended for the resuscitation of all babies at birth as recently as 2000. However, the 2005 International Liaison Committee on Resuscitation (ILCOR) recommendations allow for the initiation of resuscitation with concentrations of oxygen between 21 and 100%. There are strong arguments in favour of a radical curtailment of the use of oxygen in resuscitation at birth, and for devoting resources to defining the margins of safety for its use in the neonatal period in general.

Resuscitation with 100%, compared with 21%, oxygen following brief, repeated periods of apnea can protect vulnerable neonatal brain regions from apoptotic injury

PURPOSE

To determine the effect of repeated intermittent apnea and resuscitation with 100% vs. 21% oxygen enriched gas on levels of key regulatory proteins contributing to cell death (Bax, Caspase-3) or protecting neurons from hypoxic/ischemic injury (Bcl-2, p-Akt, p-CREB).

METHODS

The anaesthetized, mechanically ventilated newborn piglets underwent 10 episodes of apnea with resuscitation either with 100% or with 21% oxygen. Following 6h recovery the animals were sacrificed painlessly, the brain dissected out and used to determine levels of Bcl-2, Bax, Caspase-3, p-Akt and p-CREB in the striatum, frontal cortex, midbrain and hippocampus were studied.

RESULTS

In hippocampus and striatum, Bcl-2 expression was higher with 100% vs. 21% group (173+/-29% vs. 121+/-31%, p<0.05 and 189+/-10% vs. 117+/-47%, p<0.01, respectively) whereas the Bax expression was lower (88+/-3% vs. 100+/-9%, p<0.05 and 117+/-5% vs. 133+/-10%, p<0.05, respectively). Expression of Caspase-3 in the striatum, was lower with 100% vs. 21% group (197+/-35% vs. 263+/-33%, p<0.05, respectively) but not different in the hippocampus. p-Akt expression was higher with 100% vs. 21% oxygen in the hippocampus and striatum (225+/-44% vs. 108+/-35%, p<0.01 and 215+/-12% vs. 164+/-16%, p<0.01, respectively). The p-CREB expression was higher with 100% vs. 21% oxygen resuscitation in the hippocampus (217+/-41% vs. 132+/-30%, p<0.01) with no changes in striatum. Much smaller or insignificant differences between 100% vs. 21% oxygen groups were observed in the frontal cortex and midbrain, respectively.

CONCLUSION

In neonatal piglet model of intermittent apnea, selectively vulnerable regions of brain (striatum and hippocampus) are better protected from apoptotic injury when resuscitation was conducted with 100%, rather than 21%, oxygen.

New Australian Neonatal Resuscitation Guidelines

New Australian Neonatal Resuscitation Guidelines highlight the recent advances in neonatal resuscitation. Resuscitation should start with air and only use oxygen if the infant does not respond. CPAP and PEEP should be considered for premature infants with meconium stained liquor. Sucking out the mouth and nose is not necessary. Infants less than 28 weeks gestation should be placed in a polyethylene bag or wrap to keep warm. Chest compressions, when required, remain at 3:1 inflation. The endotracheal tube position must be verified with a carbon dioxide detector.

The effect of hypoxemic resuscitation of hemorrhagic shock on hemodynamic stabilization and inflammatory response: a pilot study in a rat experimental model

BACKGROUND

Resuscitation of hemorrhagic shock is associated with tissue injury. The effect of hypoxemia during resuscitation was investigated.

METHODS

Shock was induced by withdrawing blood to mean arterial pressure (MAP) 40 mm Hg and maintained for 60 minutes in 25 Wistar rats. Animals were randomly divided to receive either normoxemic (controls, FiO2 = 21%, n = 14) or hypoxemic (HypRes, FiO2 = 12%, n = 11) resuscitation by re-infusing their shed blood. Outcome was assessed through hemodynamic and inflammatory parameters. Another nine rats served to correlate different FiO2 to the corresponding PaO2.

RESULTS

At 60 minutes of resuscitation HypRes had higher MAP than control animals (p = 0.008). The respective median (range) malondialdehyde and TNF-alpha levels was 1.7 (1-2.1) versus 3.1 (2.4-4.3) micromol/L, (p = 0.02) and 0 versus 5.8 (0-5.8) pg/mL, (p = 0.025). Glutathione, endotoxin, interferon-gamma, and nitric oxide values were similar between groups. FiO2 of 12% induced only a mild hypoxemia (PaO2 approximately 80 mm Hg).

CONCLUSIONS

Even mild hypoxemia during resuscitation of shock leads to effective hemodynamic stabilization.

Avoiding hyperoxia in infants < or = 1250 g is associated with improved short- and long-term outcomes

OBJECTIVE

To determine the rate and severity of short- and long-term morbidity in very low birth weight infants treated before and after the implementation of a change in clinical practice designed to avoid hyperoxia.

METHODS

Analysis of a prospectively collected database of all infants < or = 1250 g admitted to two Emory University NICU's from January 2000 to December 2004. A change in practice was instituted in January 2003 with the objective of avoiding hyperoxia in preterm infants with target O2 saturation (SpO2) at 93 to 85% (Period II). Before the change in practice, SpO2 high alarms were set at 100% and low alarms at 92% (Period I). Statistical analysis included bivariate analyses and multivariate logistic regression comparing outcomes between the two periods.

RESULTS

From January 2000 to December 2004, 502 infants met enrollment criteria and 202 (40%) were born in period II, after change in SpO2 targets. Birth weight, gestational age and survival were similar between both periods. The rates for any retinopathy of prematurity, supplemental oxygen at 36 weeks post-conceptional age and the use of steroids for chronic lung disease were significantly lower in the infants born in Period II. There was no difference in the rates of necrotizing enterocolitis, intraventricular hemorrhage and periventricular leukomalacia. At 18 months corrected age (CA), the infants treated during Period II had a higher Mental Developmental Index (MDI) scores (80.2 +/- 18.3 vs 89.2 +/- 18.5; P 0.02) and similar Psychomotor Developmental Index (PDI) scores (83.9 +/- 18.6 vs 89.4 +/- 17.2; P 0.08) than those treated during Period I. The proportion of infants with an MDI or a PDI less than 70 was similar between the periods.

CONCLUSIONS

The change in practice to avoid hyperoxia is associated with a significant decrease in neonatal morbidity and does not have a detrimental effect on developmental outcomes at 18 months CA.

Reoxygenation with 100% oxygen versus room air: late neuroanatomical and neurofunctional outcome in neonatal mice with hypoxic-ischemic brain injury

Study investigated neuroutcome in mice subjected at 7-8 d of life to hypoxic-ischemic brain injury (HI) followed by 30 min of reoxygenation with 100% O(2) (Re-O(2)) or room air (Re-Air). At 24 h of recovery, mouse reflexes were tested. At 7 wks after HI spatial orientation and memory were assessed in the same mice. Mortality rate was recorded at 24 h and at 7 wks of recovery. In separate cohort of mice, changes in cerebral blood flow (CBF) during HI-insult and reoxygenation were recorded. Re-O(2)versus Re-Air mice exhibited significantly delayed geotaxis reflex. Adult Re-O(2)versus Re-Air mice exhibited significantly better spatial learning and orientation with strong tendency toward better preserved memory. Histopathology revealed significantly less hippocampal atrophy in Re-O(2)versus Re-Air mice. Following a hypoxia-induced hypoperfusion, Re-O(2) re-established CBF in the ipsilateral side to the prehypoxic level significantly faster than Re-Air. The mortality was higher among Re-O2 versus Re-Air mice, although, it did not reach statistical significance. Re-O(2)versus Re-Air restores CBF significantly faster and results in better late neuroutcome. However, greater early motor deficit and higher mortality rate among Re-O(2)versus Re-Air mice suggest that Re-O(2) may be deleterious at the early stage of recovery.

Air or 100% oxygen in neonatal resuscitation?

For more than 100 years, three principles have guided the treatment of neonatal asphyxia: maintain body heat, free air passages of obstructions, and stimulate respiration by supplying air to the lungs for oxygenation of the blood. This article addresses the question of which gas, air or 100% oxygen, is best supplied to the lungs to stimulate respiration. Evidence-based studies are presented and discussed.

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

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

Room air resuscitation versus oxygen resuscitation in the delivery room

The use of 100% oxygen for delivery room resuscitation is currently the recommended standard of the American Academy of Pediatrics and the Neonatal Resuscitation Program. However, there is mounting evidence from animal and human studies suggesting that resuscitation with room air (RA, 21% oxygen), including positive pressure ventilation with bag and face mask, may be as effective as that with 100% oxygen, and that the use of 100% oxygen may pose a risk of adverse physiologic sequelae. Resuscitation with RA has been demonstrated to result in faster recovery and improved neonatal mortality in comparison to 100% oxygen resuscitation. In addition, studies of normal oxygen saturation immediately after birth suggest delivery room personnel may be rushing to high saturation unnecessarily. The question for perinatal medical and nursing personnel involved in newborn resuscitation in the delivery room is whether the use of RA reduces the possible adverse effects of 100% oxygen, including delay in short-term stabilization, death, neurological disability, and possible secondary oxygen free radical injury. A systematic synopsis of both animal studies and human studies involving the advantages, disadvantages, possible risks, and short- and long-term effects of these 2 methods of resuscitation is presented.

Room air resuscitation-two decades of neonatal research

Experimental as well as clinical studies have demonstrated that room air is as efficient as pure oxygen for newborn resuscitation. Recent data even indicate that outcome is improved if pure oxygen is avoided. Thus, in a meta-analysis, neonatal mortality was significantly lower in those newly born infants resuscitated with 21% than with 100% oxygen. Short-term recovery is also improved in the room air group since time to first breath is shorter, heart rate at 90 s and 5 min Apgar score are higher. Animal data indicate that injury in a number of organs, including the brain, is aggravated by giving pure oxygen to newly born depressed infants even for a brief period. Although the optimal oxygen concentration probably is not known for newborn infants in need of resuscitation, pure oxygen should be avoided. These data should be reflected in new guidelines that are under way.

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.

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

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

Reoxygenation with 100 or 21% Oxygen after Cerebral Hypoxemia-Ischemia-Hypercapnia in Newborn Piglets

We tested if reoxygenation with 100% O(2) was superior to 21% O(2) after combined cerebral hypoxemia-ischemia-hypercapnia (HIH) in newborn piglets. Twenty-eight piglets were randomized to reoxygenation with 100 or 21% O(2) following asphyxia. Asphyxia was induced by ventilation with 8% O(2), adding CO(2), and temporary occlusion of both common carotid arteries. After 20 min, reoxygenation-reperfusion was started with 21% O(2) (HIH 21% group, n = 13) or 100% O(2) (HIH 100% group, n = 11) for 30 min followed by 21% O(2). All piglets were observed for 2 h. We measured mean arterial blood pressure (MABP), changes in microcirculation in the cerebral cortex (laser Doppler), and extracellular concentrations of hypoxanthine in the cortex and amino acids in the striatum (microdialysis). We found significantly higher MABP and better restoration of microcirculation after reoxygenation with 100% compared with 21% O(2), but no differences in biochemical markers were found between the groups. This indicates that the brain tolerated reoxygenation with 21% as well as with 100% O(2) in the present model of experimental asphyxia in spite of the differences in MABP and cerebral microcirculation.

Resuscitation of newborn infants with 21% or 100% oxygen: follow-up at 18 to 24 months

OBJECTIVE

To follow-up children who had been resuscitated at birth with either 21% or 100% oxygen (O2).

METHODS

A multicenter study with 10 participating centers recruited 609 infants to the Resair 2 study where resuscitation was performed with either 21% or 100% O2. A follow-up between ages 18 and 24 months was performed. However, during follow-up registration, it was found that 18 infants had been enrolled twice in the original Resair 2 study with different registration numbers, leaving 591 enrolled in the Resair 2 study and 410 enrolled in the 7 centers participating in the follow-up. Of these 410 infants, 79 died (76 in the neonatal and 3 in the postneonatal period). Furthermore, for 8 infants informed consent was not obtained, leaving 323 eligible for follow-up. Of these, 213 infants (66%) were followed-up: 91 (62%) had been resuscitated with 21% O2, and 122 (69%) with 100% O2. At a median age of 22 and 20 months (not significant) in the 21% and 100% groups, respectively, a simple questionnaire was filled out and neurologic assessment was performed in addition to measuring anthropometric data.

RESULTS

There were no significant differences in weight, height, or head circumference between the 2 groups. Cerebral palsy developed in 10% and 7%, respectively, in the 2 groups (not significant). In total, 11 cases (12%) in the 21% versus 11 cases (9%) in the 100% O(2) group (odds ratio: 1.39, 95% confidence interval: 0.57-3.36) developed cerebral palsy and/or mental or other delay. Furthermore, it was concluded that 14 (15%) in the 21% group and 12 (10%) in the 100% group were not normal (odds ratio: 1.67, 95% confidence interval: 0.73-3.80).

CONCLUSIONS

There were no significant differences in somatic growth or neurologic handicap at an age of 18 to 24 months in infants resuscitated with either 21% or 100% O2 at birth. Based on these data, resuscitation with ambient air seems to be safe, at least in most cases. More studies are needed to settle this issue.