The Fetus Can Teach Us: Oxygen and the Pulmonary Vasculature

Noninvasive Tracking of Embryonic Cardiac Dynamics and Development with Volumetric Optoacoustic Spectroscopy

Noninvasive monitoring of cardiac development can potentially prevent cardiac anomalies in adulthood. Mouse models provide unique opportunities to study cardiac development and disease in mammals. However, high-resolution noninvasive functional analyses of murine embryonic cardiac models are challenging because of the small size and fast volumetric motion of the embryonic heart, which is deeply embedded inside the uterus. In this study, a real time volumetric optoacoustic spectroscopy (VOS) platform for whole-heart visualization with high spatial (100 µm) and temporal (10 ms) resolutions is developed. Embryonic heart development on gestational days (GDs) 14.5-17.5 and quantify cardiac dynamics using time-lapse-4D image data of the heart is followed. Additionally, spectroscopic recordings enable the quantification of the blood oxygenation status in heart chambers in a label-free and noninvasive manner. This technology introduces new possibilities for high-resolution quantification of embryonic heart function at different gestational stages in mammalian models, offering an invaluable noninvasive method for developmental biology.

Oxygen Targets in Neonatal Pulmonary Hypertension: Individualized, "Precision-Medicine" Approach

Oxygen is a specific pulmonary vasodilator. Hypoxemia causes pulmonary vasoconstriction, and normoxia leads to pulmonary vasodilation. However, hyperoxia does not enhance pulmonary vasodilation but causes oxidative stress. There are no clinical trials evaluating optimal oxygen saturation or Pao2 in pulmonary hypertension. Data from translational studies and case series suggest that oxygen saturation of 90% to 97% or Pao2 between 50 and 80 mm Hg is associated with the lowest pulmonary vascular resistance.

Early Pulmonary Hypertension in Preterm Infants

Pulmonary hypertension (PH) in preterm neonates has multifactorial pathogenesis with unique characteristics. Premature surfactant-deficient lungs are injured following exposure to positive pressure ventilation and high oxygen concentrations resulting in variable phenotypes of PH. The prevalence of early PH is variable and reported to be between 8% and 55% of extremely preterm infants. Disruption of the lung development and vascular signaling pathway could lead to abnormal pulmonary vascular transition. The management of early PH and the off-label use of selective pulmonary vasodilators continue to be controversial.

Pulmonary Vascular Regulation in the Fetal and Transitional Lung

Fetal lungs have fewer and smaller arteries with higher pulmonary vascular resistance (PVR) than a newborn. As gestation advances, the pulmonary circulation becomes more sensitive to changes in pulmonary arterial oxygen tension, which prepares them for the dramatic drop in PVR and increase in pulmonary blood flow (PBF) that occur when the baby takes its first few breaths of air, thus driving the transition from fetal to postnatal circulation. Dynamic and intricate regulatory mechanisms control PBF throughout development and are essential in supporting gas exchange after birth. Understanding these concepts is crucial given the role the pulmonary vasculature plays in the development of complications with transition, such as in the setting of persistent pulmonary hypertension of the newborn and congenital heart disease. An improved understanding of pulmonary vascular regulation may reveal opportunities for better clinical management.

Value of brain tissue oxygen saturation in neonatal respiratory distress syndrome: a clinical study

Neonatal respiratory distress syndrome (NRDS) is one of the major causes of pre-term mortality and morbidity among very-low-birth-weight infants (VLBWI) in low- and middle-income countries (LMIC). Some of the neonates pass away despite admission and care in intensive care units (ICUs). The present clinical trial seeks the application value of elevating oxygen saturation in the brain cells of pre-term neonates born with NRDS. Near-infrared spectroscopy (NIRS) was used to monitor the neonates' microscopic cerebral oxygenation levels do determine hemoglobin concentration in brain tissues, whereas the pulse oximetry was used to measure oxygenation levels among the patients. In statistical analyses, the Analysis of Variance (ANOVA), and descriptive statistics was deployed in the Jupyter Notebook environment using Python language. High saturation of oxygen in the brain tissues result in important biological and physiological processes, including enhanced oxygen supply to cells, reduced severity of NRDS, and balancing oxygen demand and supply. The correlations of oxygen saturation with systemic saturation of oxygen, the saturation of oxygen in brain tissues, the association between brain-specific and systemic saturation, and the impact of these outcomes on clinical practices were deliberated. Also, the pH gas values, the saturation of oxygen in neonates' brain tissues, metabolic acidosis, the effect of acid-base balance and cerebral oxygen supply, and the oxygenation of brain tissues and the pH values emerged as important variables of oxygenation of brain tissues in pre-term neonates. Oxygen saturation in brain cells influence vital physiological and biological processes. Balancing acid-base saturation or levels is needed despite the challenging achievement. Oxygenation of brain tissues improve the brain's overall functioning.

Optimal oxygen use in neonatal advanced cardiopulmonary resuscitation-a literature review

Background and Objectives

Oxygen (O2) use during neonatal cardiopulmonary resuscitation (CPR) remains a subject of controversy. The inspired O2 concentration during neonatal CPR, that hastens return of spontaneous circulation (ROSC), allows adequate cerebral and myocardial O2 delivery, and enhances survival to discharge, is not known. The optimal FiO2 during CPR should decrease incidence of hypoxia but also avoid hyperoxia, and ultimately lead to improved neurodevelopmental outcomes. Due to infrequent need for extensive resuscitation, and emergent circumstances surrounding neonatal CPR, conducting randomized clinical trials continues to be a challenge. The goal of this study was to review the evolution of oxygen use during neonatal CPR, the evidence from animal and clinical studies on oxygen use during neonatal CPR and after ROSC, the pertinent physiology including myocardial oxygen consumption and cerebral oxygen delivery during CPR, and outcomes following CPR in the DR and in the neonatal intensive care unit.

Methods

This narrative review is based on recent and historic English literature in PubMed and Google scholar over the past 35 years (January 1, 1985 - May 1, 2021).

Key Content and Findings

Several studies in animal models have compared ventilation with different inspired O2 concentrations (mostly 21% and 100%) during chest compressions and after ROSC. These studies reported no difference in short-term outcomes, even with as low as 18% O2. However, in lamb models of cardiac arrest and CPR, 100% O2 during chest compressions is associated with better oxygen delivery to the brain compared to 21% O2. Abrupt weaning to 21% O2 following ROSC followed by titration to achieve preductal SpO2 of 85-95% minimizes systemic hyperoxia and oxidative stress compared to slow weaning from 100% O2 following ROSC.

Conclusions

Clinical research is needed to arrive at the best strategy for assessment of oxygenation and choice of FiO2 during neonatal CPR that lead to improved survival and outcomes. In this article, we have reviewed the literature on evidence behind O2 use during neonatal advanced CPR and after ROSC.

Does Perinatal Intermittent Hypoxia Affect Cerebrovascular Network Development?

Perinatal hypoxia is an inadequate delivery of oxygen to the fetus in the period immediately before, during, or after the birth process. The most frequent form of hypoxia occurring in human development is chronic intermittent hypoxia (CIH) due to sleep-disordered breathing (apnea) or bradycardia events. CIH incidence is particularly high with premature infants. During CIH, repetitive cycles of hypoxia and reoxygenation initiate oxidative stress and inflammatory cascades in the brain. A dense microvascular network of arterioles, capillaries, and venules is required to support the constant metabolic demands of the adult brain. The development and refinement of this microvasculature is orchestrated throughout gestation and in the initial weeks after birth, at a critical juncture when CIH can occur. There is little knowledge on how CIH affects the development of the cerebrovasculature. However, since CIH (and its treatments) can cause profound abnormalities in tissue oxygen content and neural activity, there is reason to believe that it can induce lasting abnormalities in vascular structure and function at the microvascular level contributing to neurodevelopmental disorders. This mini-review discusses the hypothesis that CIH induces a positive feedback loop to perpetuate metabolic insufficiency through derailment of normal cerebrovascular development, leading to long-term deficiencies in cerebrovascular function.

Impact of the Addition of a Centrifugal Pump in a Preterm Miniature Pig Model of the Artificial Placenta

The recent demonstration of normal development of preterm sheep in an artificial extrauterine environment has renewed interest in artificial placenta (AP) systems as a potential treatment strategy for extremely preterm human infants. However, the feasibility of translating this technology to the human preterm infant remains unknown. Here we report the support of 13 preterm fetal pigs delivered at 102 ± 4 days (d) gestation, weighing 616 ± 139 g with a circuit consisting of an oxygenator and a centrifugal pump, comparing these results with our previously reported pumpless circuit (n = 12; 98 ± 4 days; 743 ± 350 g). The umbilical vessels were cannulated, and fetuses were supported for 46.4 ± 46.8 h using the pumped AP versus 11 ± 13 h on the pumpless AP circuit. Upon initiation of AP support on the pumped system, we observed supraphysiologic circuit flows, tachycardia, and hypertension, while animals maintained on a pumpless AP circuit exhibited subphysiologic flows. On the pumped AP circuit, there was a progressive decline in umbilical vein (UV) flow and oxygen delivery. We conclude that the addition of a centrifugal pump to the AP circuit improves survival of preterm pigs by augmenting UV flow through the reduction of right ventricular afterload. However, we continued to observe the development of heart failure within a matter of days.

Prenatal Hypoxia Affects Foetal Cardiovascular Regulatory Mechanisms in a Sex- and Circadian-Dependent Manner: A Review

Prenatal hypoxia during the prenatal period can interfere with the developmental trajectory and lead to developing hypertension in adulthood. Prenatal hypoxia is often associated with intrauterine growth restriction that interferes with metabolism and can lead to multilevel changes. Therefore, we analysed the effects of prenatal hypoxia predominantly not associated with intrauterine growth restriction using publications up to September 2021. We focused on: (1) The response of cardiovascular regulatory mechanisms, such as the chemoreflex, adenosine, nitric oxide, and angiotensin II on prenatal hypoxia. (2) The role of the placenta in causing and attenuating the effects of hypoxia. (3) Environmental conditions and the mother's health contribution to the development of prenatal hypoxia. (4) The sex-dependent effects of prenatal hypoxia on cardiovascular regulatory mechanisms and the connection between hypoxia-inducible factors and circadian variability. We identified that the possible relationship between the effects of prenatal hypoxia on the cardiovascular regulatory mechanism may vary depending on circadian variability and phase of the days. In summary, even short-term prenatal hypoxia significantly affects cardiovascular regulatory mechanisms and programs hypertension in adulthood, while prenatal programming effects are not only dependent on the critical period, and sensitivity can change within circadian oscillations.

Oxygen saturation and heart rate in healthy term and late preterm infants with delayed cord clamping

Blood oxygen in the fetus is substantially lower than in the newborn infant. In the minutes after birth, arterial oxygen saturation rises from around 50-60% to 90-95%. Initial respiratory efforts generate negative trans-thoracic pressures that drive liquid from the airways into the lung interstitium facilitating lung aeration, blood oxygenation, and pulmonary artery vasodilatation. Consequently, intra- (foramen ovale) and extra-cardiac (ductus arteriosus) shunting changes and the sequential circulation switches to a parallel pulmonary and systemic circulation. Delaying cord clamping preserves blood flow through the ascending vena cava, thus increasing right and left ventricular preload. Recently published reference ranges have suggested that delayed cord clamping positively influenced the fetal-to-neonatal transition. Oxygen saturation in babies with delayed cord clamping plateaus significantly earlier to values of 85-90% than in babies with immediate cord clamping. Delayed cord clamping may also contribute to fewer episodes of brady-or-tachycardia in the first minutes after birth, but data from randomized trials are awaited. IMPACT: Delaying cord clamping during fetal to neonatal transition contributes to a significantly earlier plateauing of oxygen saturation and fewer episodes of brady-and/or-tachycardia in the first minutes after birth. We provide updated information regarding the changes in SpO2 and HR during postnatal adaptation of term and late preterm infants receiving delayed compared with immediate cord clamping. Nomograms in newborn infants with delayed cord clamping will provide valuable reference ranges to establish target SpO2 and HR in the first minutes after birth.

Hemodynamic consequences of respiratory interventions in preterm infants

Advances in perinatal management have led to improvements in survival rates for premature infants. It is known that the transitional period soon after birth, and the subsequent weeks, remain periods of rapid circulatory changes. Preterm infants, especially those born at the limits of viability, are susceptible to hemodynamic effects of routine respiratory care practices. In particular, the immature myocardium and cardiovascular system is developmentally vulnerable. Standard of care (but essential) respiratory interventions, administered as part of neonatal care, may negatively impact heart function and/or pulmonary or systemic hemodynamics. The available evidence regarding the hemodynamic impact of these respiratory practices is not well elucidated. Enhanced diagnostic precision and therapeutic judiciousness are warranted. In this narrative, we outline (1) the vulnerability of preterm infants to hemodynamic disturbances (2) the hemodynamic effects of common respiratory practices; including positive pressure ventilation and surfactant therapy, and (3) identify tools to assess cardiopulmonary interactions and guide management.

Inhaled Nitric Oxide at Birth Reduces Pulmonary Vascular Resistance and Improves Oxygenation in Preterm Lambs

Resuscitation with 21% O₂ may not achieve target oxygenation in preterm infants and in neonates with persistent pulmonary hypertension of the newborn (PPHN). Inhaled nitric oxide (iNO) at birth can reduce pulmonary vascular resistance (PVR) and improve PaO₂. We studied the effect of iNO on oxygenation and changes in PVR in preterm lambs with and without PPHN during resuscitation and stabilization at birth. Preterm lambs with and without PPHN (induced by antenatal ductal ligation) were delivered at 134 d gestation (term is 147–150 d). Lambs without PPHN were ventilated with 21% O₂, titrated O₂ to maintain target oxygenation or 21% O₂ + iNO (20 ppm) at birth for 30 min. Preterm lambs with PPHN were ventilated with 50% O₂, titrated O₂ or 50% O₂ + iNO. Resuscitation with 21% O₂ in preterm lambs and 50%O₂ in PPHN lambs did not achieve target oxygenation. Inhaled NO significantly decreased PVR in all lambs and increased PaO₂ in preterm lambs ventilated with 21% O₂ similar to that achieved by titrated O₂ (41 ± 9% at 30 min). Inhaled NO increased PaO₂ to 45 ± 13, 45 ± 20 and 76 ± 11 mmHg with 50% O₂, titrated O₂ up to 100% and 50% O₂ + iNO, respectively, in PPHN lambs. We concluded that iNO at birth reduces PVR and FiO₂ required to achieve target PaO₂.

Neonatal and Postneonatal Pulmonary Hypertension

During transition at birth with ventilation of the lungs, pulmonary vascular resistance (PVR) decreases from high fetal values, leading to an 8 to 10-fold increase in pulmonary blood flow (Qp). In some infants, this transition does not occur, resulting in pulmonary hypertension (PH). In infants, PH can present as: (a) primary PH in term neonates (idiopathic), (b) PH secondary to lung disease or hypoplasia in term infants, (c) acute PH in preterm infants with respiratory distress syndrome (RDS), (d) chronic PH with bronchopulmonary dysplasia (BPD) in preterm infants and (e) post-neonatal PH. A hemodynamically significant patent ductus arteriosus (PDA) can exacerbate PH in preterm infants due to increased Qp. Pulmonary vein stenosis (PVS) can complicate BPD with PH. Diagnosis of PH is based on clinical features, echocardiography and, in some intractable cases, cardiac catheterization. Therapy of PH includes oxygen, invasive or non-invasive ventilation, correction of acidosis, surfactant and selective and non-selective pulmonary vasodilators such as inhaled nitric oxide and sildenafil, respectively. Early closure of a hemodynamically significant PDA has the potential to limit pulmonary vascular remodeling associated with BPD and PH. The role of thiamine in pathogenesis of PH is also discussed with the recent increase in thiamine-responsive acute pulmonary hypertension in early infancy. Recognition and prompt therapy of PH can prevent right ventricular dysfunction, uncoupling and failure.

Metabolic environment in vivo as a blueprint for differentiation and maturation of human stem cell-derived cardiomyocytes

Patient-derived human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are increasingly being used for disease modeling, drug screening and regenerative medicine. However, to date, an immature, fetal-like, phenotype of hPSC-CMs restrains their full potential. Increasing evidence suggests that the metabolic state, particularly important for provision of sufficient energy in highly active contractile CMs and anabolic and regulatory processes, plays an important role in CM maturation, which affects crucial functional aspects of CMs, such as contractility and electrophysiology. During embryonic development the heart is subjected to metabolite concentrations that differ substantially from that of hPSC-derived cardiac cell cultures. A deeper understanding of the environmental and metabolic cues during embryonic heart development and how these change postnatally, will provide a framework for optimizing cell culture conditions and maturation of hPSC-CMs. Maturation of hPSC-CMs will improve the predictability of disease modeling, drug screening and drug safety assessment and broadens their applicability for personalized and regenerative medicine.

Oxygen Supplementation During Preterm Stabilization and the Relevance of the First 5 min After Birth

Fetal to neonatal transition entails cardiorespiratory, hemodynamic, and metabolic changes coinciding with the switch from placental to airborne respiration with partial pressures of oxygen of 4-5 kPa in utero raising to 8-9 kPa ex utero in few minutes. Preterm infants have immature lung and antioxidant defense system. Very preterm infants (<32 weeks' gestation) frequently require positive pressure ventilation and oxygen to establish lung aeration, a functional residual capacity, and overcome a tendency toward hypoxemia and bradycardia in the first minutes after birth. Recent studies have shown that prolonged bradycardia (heart rate <100 beats per minute) and/or hypoxemia (oxygen saturation <80%) are associated with increased mortality and/or intracranial hemorrhage. However, despite the accumulated evidence, the way in which oxygen should be supplemented in the first minutes after birth still has not yet been clearly established. The initial inspired fraction of oxygen and its adjustment within a safe arterial oxygen saturation range measured by pulse oximetry that avoids hyper-or-hypoxia is still a matter of debate. Herewith, we present a current summary aiming to assist the practical neonatologist who has to aerate the lung and establish an efficacious respiration in very preterm infants in the delivery room.

Perinatal Management of Bart's Hemoglobinopathy: Paradoxical Effects of Intrauterine, Transplacental, and Partial Exchange Transfusions

We describe a fetus at 24 ^3/7 weeks' gestation that showed ultrasound evidence of anemia, hydrops, and severe growth restriction. Both parents were known to be cis heterozygous carriers for SEA α-thalassemia deletion (αα/-). Cordocentesis confirmed fetal anemia and homozygous α-thalassemia (-/-) in the fetus. Fetal intrauterine transfusions corrected the anemia, treated the hydrops, and improved fetal growth. The postnatal course was complicated by hypoxic respiratory failure and persistent pulmonary hypertension of the newborn, which resolved only after partial volume exchange transfusion. This case report is presented to point out the potential unintended outcomes with transplacental transfusion via delayed cord clamping and cord milking at delivery in the setting of congenital Bart's hemoglobinopathy, and demonstrates that partial exchange transfusion of the newborn may optimize oxygen delivery due to the more favorable oxygen affinity of transfused adult hemoglobin compared with the Bart's hemoglobin.

Gestational Hypoxia and Programing of Lung Metabolism

Gestational hypoxia is a risk factor in the development of pulmonary hypertension in the newborn and other sequela, however, the mechanisms associated with the disease remain poorly understood. This review highlights disruption of metabolism by antenatal high altitude hypoxia and the impact this has on pulmonary hypertension in the newborn with discussion of model organisms and human populations. There is particular emphasis on modifications in glucose and lipid metabolism along with alterations in mitochondrial function. Additional focus is placed on increases in oxidative stress and the progression of pulmonary vascular disease in the newborn and on the need for further exploration using a combination of contemporary and classical approaches.

Pharmacokinetic modeling of intravenous sildenafil in newborns with congenital diaphragmatic hernia

PURPOSE

We developed a pharmacokinetic model of intravenous sildenafil in newborns with congenital diaphragmatic hernia (CDH) to achieve a target plasma concentration of over 50 μg/l.

METHODS

Twenty-three CDH newborns with pulmonary hypertension (64 blood samples) received intravenous sildenafil. Patients received a loading dose of 0.35 mg/kg (IQR 0.16 mg/kg) for 3 h, followed by a continuous infusion of 1.5 mg/kg/day (IQR 0.1 mg/kg/day). For model development, non-linear mixed modeling was used. Inter-individual variability (IIV) and inter-occasion variability were tested. Demographic and laboratory parameters were evaluated as covariates. Normalized prediction distribution errors (NPDE) and visual predictive check (VPC) were used for model validation.

RESULTS

A two-compartment disposition model of sildenafil and a one-compartment disposition model of desmethyl sildenafil (DMS) was observed with IIV in sildenafil and DMS clearance and volume of distribution of sildenafil. NPDE and VPC revealed adequate predictability. Only postnatal age increased sildenafil clearance. This was partly compensated by a higher DMS concentration, which also has a therapeutic effect. In this small group of patients, sildenafil was tolerated well.

CONCLUSIONS

This model for sildenafil in CDH patients shows that concentration-targeted sildenafil dosing of 0.4 mg/kg in 3 h, followed by 1.6 mg/kg/day continuous infusion achieves appropriate sildenafil plasma levels.

The CoDiNOS trial protocol: an international randomised controlled trial of intravenous sildenafil versus inhaled nitric oxide for the treatment of pulmonary hypertension in neonates with congenital diaphragmatic hernia

INTRODUCTION

Congenital diaphragmatic hernia (CDH) is a developmental defect of the diaphragm that impairs normal lung development, causing pulmonary hypertension (PH). PH in CDH newborns is the main determinant for morbidity and mortality. Different therapies are still mainly based on 'trial and error'. Inhaled nitric oxide (iNO) is often the drug of first choice. However, iNO does not seem to improve mortality. Intravenous sildenafil has reduced mortality in newborns with PH without CDH, but prospective data in CDH patients are lacking.

METHODS AND ANALYSIS

In an open label, multicentre, international randomised controlled trial in Europe, Canada and Australia, 330 newborns with CDH and PH are recruited over a 4-year period (2018-2022). Patients are randomised for intravenous sildenafil or iNO. Sildenafil is given in a loading dose of 0.4 mg/kg in 3 hours; followed by continuous infusion of 1.6 mg/kg/day, iNO is dosed at 20 ppm. Primary outcome is absence of PH on day 14 without pulmonary vasodilator therapy and/or absence of death within the first 28 days of life. Secondary outcome measures include clinical and echocardiographic markers of PH in the first year of life. We hypothesise that sildenafil gives a 25% reduction in the primary outcome from 68% to 48% on day 14, for which a sample size of 330 patients is needed. An intention-to-treat analysis will be performed. A p-value (two-sided) <0.05 is considered significant in all analyses.

ETHICS AND DISSEMINATION

Ethics approval has been granted by the ethics committee in Rotterdam (MEC-2017-324) and the central Committee on Research Involving Human Subjects (NL60229.078.17) in the Netherlands. The principles of the Declaration of Helsinki, the Medical Research Involving Human Subjects Act and the national rules and regulations on personal data protection will be used. Parental informed consent will be obtained.

TRIAL REGISTRATION NUMBER

NTR6982; Pre-results.

Human Umbilical Vein Endothelial Cells (HUVECs) Co-Culture with Osteogenic Cells: From Molecular Communication to Engineering Prevascularised Bone Grafts

The repair of bone defects caused by trauma, infection or tumor resection is a major clinical orthopedic challenge. The application of bone grafts in orthopedic procedures is associated with a problem of inadequate vascularization in the initial phase after implantation. Meanwhile, the survival of cells within the implanted graft and its integration with the host tissue is strongly dependent on nutrient and gaseous exchange, as well as waste product removal, which are effectuated by blood microcirculation. In the bone tissue, the vasculature also delivers the calcium and phosphate indispensable for the mineralization process. The critical role of vascularization for bone healing and function, led the researchers to the idea of generating a capillary-like network within the bone graft in vitro, which could allow increasing the cell survival and graft integration with a host tissue. New strategies for engineering pre-vascularized bone grafts, that apply the co-culture of endothelial and bone-forming cells, have recently gained interest. However, engineering of metabolically active graft, containing two types of cells requires deep understanding of the underlying mechanisms of interaction between these cells. The present review focuses on the best-characterized endothelial cells-human umbilical vein endothelial cells (HUVECs)-attempting to estimate whether the co-culture approach, using these cells, could bring us closer to development and possible clinical application of prevascularized bone grafts.

Targeting Oxygen in Term and Preterm Infants Starting at Birth

Transition into the extrauterine world is characterized by a substantial increase in oxygen availability to tissue. Exact oxygen provision may be needed to avoid negative consequences of hypoxia or hyperoxia. For term and near-term infants, it is recommended to start with air and titrate the oxygen supplement to the saturation nomogram. However, oxygen supplementation in infants less than 32 weeks' gestation is an unsolved conundrum. At present, the inspired fraction of oxygen is set according to gestational age and blended to achieve targeted saturations and heart rates. Studies are still needed to overcome uncertainties about oxygen supplementation during preterm stabilization.

Optimal Inspired Fraction of Oxygen in the Delivery Room for Preterm Infants

Postnatal adaptation of preterm infants entails a series of difficulties among which the immaturity of the respiratory system is the most vital. To overcome respiratory insufficiency, caregivers attending in the delivery room use positive pressure ventilation and oxygen. A body of evidence in relation of oxygen management in the delivery room has been accumulated in recent years; however, the optimal initial inspired fraction of oxygen, the time to achieve specific oxygen saturation targets, and oxygen titration have not been yet clearly established. The aim of this review is to update the reader by critically analyzing the most relevant literature.

Hemoglobin oxygen saturation targets in the neonatal intensive care unit: Is there a light at the end of the tunnel? 1

The optimal oxygenation target needed to prevent the extremes of hypoxia and oxygen toxicity in premature and sick newborns has been the subject of much research and debate. The advent of the pulse oximeter has allowed the continuous monitoring of oxyhemoglobin saturation and the delivery of oxygen with greater precision. Well-run, large clinical trials to determine the safest oxygen concentration have led to several revisions in guidelines for neonatal care. However, monitoring of oxyhemoglobin saturation has its limitations and does not provide a comprehensive assessment of tissue oxygenation. To identify optimal oxygen therapy, various other factors (partial pressure of arterial carbon dioxide, hemoglobin concentration, blood pH, and tissue metabolic demand) that influence perfusion and tissue oxygenation need to be considered.

Influence of Sex on Gestational Complications, Fetal-to-Neonatal Transition, and Postnatal Adaptation

Fetal sex is associated with striking differences during in utero development, fetal-to-neonatal transition, and postnatal morbidity and mortality. Male sex fetuses are apparently protected while in utero resulting in a higher secondary sex rate for males than for females. However, during fetal-to-neonatal transition and thereafter in the newborn period, female exhibits a greater degree of maturation that translates into a better capacity to stabilize, less incidence of prematurity and prematurity-associated morbidities, and better long-term outcomes. The present review addresses the influence of sex during gestation and postnatal adaptation that includes the establishment of an adult-type circulation, the initiation of breathing, endurance when confronted with perinatal hypoxia ischemia, and a gender-related different response to drugs. The intrinsic mechanisms explaining these differences in the perinatal period remain elusive and further experimental and clinical research are therefore stringently needed if an individual oriented therapy is to be developed.