Peripheral haemodynamics in newborns: best practice guidelines

Pulse Oximetry Saturation (Spo2) Monitoring in the Neonatal Intensive Care Unit (NICU): The Challenge for Providers: A Systematic Review

BACKGROUND

In the neonatal intensive care unit (NICU), maintaining an oxygenation level that avoids both hypoxemia and hyperoxemia is challenging. Pulse oximetry has become fundamental for noninvasive monitoring of saturation of peripheral oxygen (Spo2) in preterm newborns.

PURPOSE

The aim of this systematic review is to determine Spo2 target values in order to avoid hypoxemia or hyperoxemia and complications arising from these.

METHOD AND SEARCH STRATEGY

For this systematic review, articles were audited from 2010 to 2020 using the PRISMA guidelines. PubMed, MEDLINE, Google Scholar, and Scopus databases were used, and search terms were related to use of pulse oximetry in the NICU.

RESULTS

The result showed that 12 of 20 (60%) studies focused on target values but without a unanimous agreement on values, although 5 of 12 studies (41.66%) suggested a lower value target of 85% and 4 of 12 studies (33.33%) recommended 95% as the higher target value. Other authors showed no difference in the incidence of adverse events comparing different target values and focused the importance more on the fluctuation of the value than on the target value itself.

IMPLICATION FOR PRACTICE

Reaching a balance in the oxygen administration so as to avoid potential complications associated with hypoxemia or hyperoxemia is a challenge for the clinicians.

IMPLICATION FOR RESEARCH

Further studies on fluctuation of Spo2 comparing different starting targets could better clarify the role of fluctuations and the absolute target values.Video Abstract available at:https://journals.na.lww.com/advancesinneonatalcare/Pages/videogallery.aspx?autoPlay=false&videoId=49.

A vasoactive inotropic score predicts the severity of compromised systemic circulation and mortality in preterm infants

OBJECTIVE

To validate the vasoactive inotropic score as a predictor of the severity of compromised systemic circulation and mortality in preterm infants.

METHODS

A retrospective study was conducted on preterm infants with Compromised systemic circulation [hypotension±lactic acidosis±oliguria] who received a cardiovascular support, we calculated the vasoactive inotropic score (VIS) and cumulative exposure to cardiovascular medications over time (VISct). Receiver operator curve was constructed to predict the primary outcome which was death & refractory hypotension.

RESULTS

VIS had an area under the curve of 0.73 (95% CI 0.85-0.98, p <  0.001). A VIS cut off of 25 has sensitivity and specificity of 66% and 92%, and positive and negative predictive values of 78.5% and 83%, respectively.

CONCLUSION

High VIS predicts the severity of Compromised systemic circulation and mortality rate in preterm infants.

Association between Regional Tissue Oxygenation and Body Temperature in Term and Preterm Infants Born by Caesarean Section

Body temperature (BT) management remains a challenge in neonatal intensive care, especially during resuscitation after birth. Our aim is to analyze whether there is an association between the BT and cerebral and peripheral tissue oxygen saturation (crSO₂/cTOI and prSO₂), arterial oxygen saturation (SpO₂), and heart rate (HR). The secondary outcome parameters of five prospective observational studies are analyzed. We include preterm and term neonates born by Caesarean section who received continuous pulse oximetry and near-infrared spectroscopy monitoring during the first 15 min, and a rectal BT measurement once in minute 15 after birth. Four-hundred seventeen term and 169 preterm neonates are included. The BT did not correlate with crSO₂/cTOI and SpO₂. The BT correlated with the HR in all neonates (ρ = 0.210, p < 0.001) and with prSO₂ only in preterm neonates (ρ = −0.285, p = 0.020). The BT was lower in preterm compared to term infants (36.7 [36.4–37.0] vs. 36.8 [36.6–37.0], p = 0.001) and prevalence of hypothermia was higher in preterm neonates (29.5% vs. 12.0%, p < 0.001). To conclude, the BT did not correlate with SpO₂ and crSO₂/cTOI, however, there was a weak positive correlation between the BT and the HR in the whole cohort and a weak correlation between the BT and prSO₂ only in preterm infants. Preterm neonates had a statistically lower BT and suffered significantly more often from hypothermia during postnatal transition.

Assessment of neonatal perfusion

Disorders of perfusion in newborn infants are frequently observed in neonatal intensive care units. The current assessment practices are primarily based on clinical signs. Significant technologic advances have opened new avenues for continuous assessment at the bedside. Combining these devices with functional echocardiography provides an in-depth understanding of perfusion and allows targeting therapy to the pathophysiology rather than monitoring and targeting blood pressure. This change in approach is guided by the fact that perfusion disorders can result from a number of causes and a single management approach might do more harm than good. This approach has the potential to improve long term outcomes but needs to be tested in well-designed trials.

Mitochondrial Oxygen Monitoring During Surgical Repair of Congenital Diaphragmatic Hernia or Esophageal Atresia: A Feasibility Study

Current monitoring techniques in neonates lack sensitivity for hypoxia at cellular level. The recent introduction of the non-invasive Cellular Oxygen METabolism (COMET) monitor enables measuring in vivo mitochondrial oxygen tension (mitoPO2), based on oxygen-dependent quenching of delayed fluorescence of 5-aminolevulinic acid (ALA)-enhanced protoporphyrin IX. The aim is to determine the feasibility and safety of non-invasive mitoPO2 monitoring in surgical newborns. MitoPO2 measurements were conducted in a tertiary pediatric center during surgical repair of congenital diaphragmatic hernia or esophageal atresia. Intraoperative mitoPO2 monitoring was performed with a COMET monitor in 11 congenital diaphragmatic hernia and four esophageal atresia neonates with the median age at surgery being 2 days (IQR 1.25-5.75). Measurements were done at the skin and oxygen-dependent delayed fluorescence was measurable after at least 4 h application of an ALA plaster. Pathophysiological disturbances led to perturbations in mitoPO2 and were not observed with standard monitoring modalities. The technique did not cause damage to the skin, and seemed safe in this respect in all patients, and in 12 cases intraoperative monitoring was successfully completed. Some external and potentially preventable factors-the measurement site being exposed to the disinfectant chlorohexidine, purple skin marker, or infrared light-seemed responsible for the inability to detect an adequate delayed fluorescence signal. In conclusion, this is the first study showing it is possible to measure mitoPO2 in neonates and that the cutaneous administration of ALA to neonates in the described situation can be safely applied. Preliminary data suggests that mitoPO2 in neonates responds to perturbations in physiological status.

NIRS in the fetal to neonatal transition and immediate postnatal period

Near-infrared spectroscopy (NIRS) offers the non-invasive continuous monitoring of cerebral oxygenation and perfusion. Cerebral regional oxygen (crSO2) measured via NIRS represents a mixed tissue saturation value, thus enabling information on the balance of cerebral oxygen delivery and oxygen consumption. Cerebral oxygenation is influenced by pulse oximeter saturation (SpO2), hemoglobin content, and cerebral blood flow. Furthermore, cerebral oxygenation is dependent on metabolic parameters, cardio circulatory parameters, perinatal- and postnatal interventions. Reference ranges for healthy term born and late preterm infants have already been published. It is feasible to increase crSO2 values above the 10th percentile by guiding medical support during neonatal to fetal transition. Guiding oxygen supply based on NIRS monitoring in addition to SpO2 monitoring showed that a reduction of the burden of cerebral hypoxia was possible. A currently ongoing study will give further information whether additional NIRS monitoring guiding medical support during neonatal to fetal transition is effective in improving neonatal outcome.

Measurement of gut oxygenation in the neonatal population using near-infrared spectroscopy: a clinical tool?

CONTEXT

Near-infrared spectroscopy (NIRS) is a non-invasive bedside monitor of tissue oxygenation that may be a useful clinical tool in monitoring of gut oxygenation in newborn infants.

OBJECTIVE

To systematically review literature to determine whether NIRS is a reliable tool to monitor gut oxygenation on neonatal units.

DATA SOURCES

PubMed and Embase databases were searched using the terms 'neonate', 'preterm infants', 'NIRS' and 'gut oxygenation' (2001-2018).

STUDY SELECTION

Studies were included if they met inclusion criteria (clinical trial, observational studies, neonatal population, articles in English and reviewing regional gut oxygen saturations) and exclusion criteria (not evaluating abdominal NIRS or regional oxygen saturations).

DATA EXTRACTION

Two authors independently searched PubMed and Embase using the predefined terms, appraised study quality and extracted from 30 studies the study design and outcome data.

LIMITATIONS

Potential for publication bias, majority of studies were prospective cohort studies and small sample sizes.

RESULTS

Thirty studies were reviewed assessing the validity of abdominal NIRS and potential application in neonates. Studies reviewed assessed abdominal NIRS in different settings including normal neonates, bolus and continuous feeding, during feed intolerance, necrotising enterocolitis and transfusion with packed red cells. Several observational studies demonstrated how NIRS could be used in clinical practice.

CONCLUSIONS

NIRS may prove to be a useful bedside tool on the neonatal unit, working alongside current clinical tools in the monitoring of newborn infants (preterm and term) and inform clinical management. We recommend further studies including randomised controlled trials looking at specific measurements and cut-offs for abdominal NIRS for use in further clinical practice.

Neonatal hemodynamics and management of hypotension in newborns

Hemodynamic instability is frequent in high-risk infants admitted to neonatal intensive care units. However, monitoring and treatment strategies of those conditions might show variations among the units. Different factors can compromise hemodynamic status in preterm/ term infants. Treatment options mostly include volume replacement, inotropes and/or vasopressors (dopamine, dobutamine, epinephrine and milrinone) and hydrocortisone. In general, these treatments are driven by predetermined protocols, which are not patient-based. According to the current knowledge, a physiology-driven approach that takes the individual characteristics of the newborn into consideration is accepted to be more suitable. In neonatal hemodynamics, important determinants are cardiac output, systemic vascular resistance, blood pressure, regional tissue perfusion and oxygenation. The novel technological methods, "targeted neonatal echocardiography" and "near-infrared spectroscopy" can help to delineate the underlying pathophysiology better, when added to the clinical assessment. In this review, strategies for the assessment of neonatal hemodynamics, as well as etiology, monitoring, and treatment of hemodynamic instability in preterm and term infants are presented.

The future of medical education in neonatology, paediatrics and paediatric virology: An interview with Professor Alan Michael Weindling, Professor of Perinatal Medicine at the University of Liverpool

Professor Alan Michael Weindling, Emeritus Professor of Perinatal Medicine at the University of Liverpool in the UK, is one of the pioneers of modern neonatal care worldwide with an enormous contribution to the care of premature babies in the city of Liverpool. During the last 3 decades, his contributions focused on the development of the clinical service, the training provided and the strong research achievements at Liverpool Women's Hospital NHS Trust, one of the most widely respected centres for neonatal medicine in western Europe. According to Professor Weindling, teaching a commitment to continuing lifelong learning as well as trying to make clinical care cost-effective is really important. He highlights the value of humility, holistic scientific approach, evidence-based medicine and multidisciplinary team working to neonatal and paediatric care. Looking back to neonatology as practiced in the 1990s, he accepts that since then, the overall standard of care has improved enormously. He supports that further neonatal care research is required for the prevention and treatment of acquired brain damage as well as on looking at ways of minimising stress for families, who have a child in an intensive care unit. He could see how for most trainees a module or series of lectures in paediatric infectious diseases would be helpful as part of their training and he estimates that in the future paediatric virology may become a specialist interest for a limited number of paediatric trainees. In the context of the ‘4th Workshop on Paediatric Virology’, which will be held in Athens, Greece, on September 22nd, 2018, Professor Weindling will receive the ‘2018 Paediatric Virology Award in Neonatology and Medical Education’.

Perfusion monitoring and intraventricular hemorrhage in preterm infants

Cardiovascular instability in preterm infants during the early postnatal period correlates with the development of intraventricular hemorrhage (IVH). Due to the correlation between hypotension and fluctuation of blood pressure, treatment was targeted specifically at hypotension to prevent IVH, but this was not successful. Recently, several novel perfusion markers have been found to be correlated with the development of IVH, and they are of current interest in cardiovascular management. In this review, the correlation between IVH and conventional, as well as novel, perfusion markers is examined.

Integrated Evaluation of Neonatal Hemodynamics Program Optimizing Organ Perfusion and Performance in Critically Ill Neonates, Part 1: Understanding Physiology of Neonatal Hemodynamics

Integrated evaluation of neonatal hemodynamics is the integration of information obtained by echocardiography, clinical evaluation, and biochemical markers, in addition to the clinical information obtained from noninvasive and invasive monitoring of blood pressure and arterial and tissue oxygenation, leading to the formulation of a medical recommendation. This review will focus on the physiology of cardiovascular dynamics and oxygen delivery.

The impact of integrated evaluation of hemodynamics using targeted neonatal echocardiography with indices of tissue oxygenation: a new approach

OBJECTIVE

To study the impact of integrated evaluation of hemodynamics (IEH) using targeted neonatal echocardiography, together with regional tissue oxygenation, fractional oxygen extraction using near-infrared spectroscopy on the management of infants with compromised hemodynamics.

STUDY DESIGN

Retrospective cohort comparison of two groups of infants with compromised hemodynamics. EPOCH 1: did not undergo IEH (January 2012 to March 2014); EPOCH 2: underwent IEH (April 2014 to December 2015). The primary outcome was the time to recovery.

RESULTS

In all, 340 infants were included; 158 underwent IEH with a median (IQR) of 2 (1 to 3) evaluations per infant. Reasons for assessment included PDA (60%), compromised systemic circulation (14%) and clinically suspected pulmonary hypertension (22%). The time to recovery was shorter in IEH group in patients with compromised systemic circulation median (IQR), 32 h (24 to 63) compared with none IEH group 71 h (36 to 96), pulmonary hypertension 63 h (14.2 to 102) in IEH group compared with 68 h (24 to 240) in none IEH group, there were fewer PDA-related complications in preterm infants with PDA in IEH group.

CONCLUSION

IEH was associated with shorter time to clinical recovery in infants with compromised hemodynamics.

Defining hypotension in anesthetized infants by individual awake blood pressure values: a prospective observational study

BACKGROUND

Blood pressure (BP) is the most commonly applied clinical surrogate parameter for tissue perfusion and cerebral autoregulation. Hypotension during anesthesia may contribute to unfavorable outcome in young children. Hypotension in anesthetized infants can be defined using BP values relative to individual awake baseline or absolute BP values.

AIM

The aim of this study was to investigate the applicability of the two definitions and to compare the incidences of hypotension.

METHOD

This was a prospective observational study in 151 infants <12 months of age. The percentage of successful awake BP measurements was calculated and related to the infant's behavioral state. Hypotension under sevoflurane anesthesia was defined by a decrease of mean arterial pressure (MAP) relative to awake baseline (>20% in infants <6 months, >40% in infants >6 months) or absolute MAP values (<35 mmHg in infants <6 months, <43 mmHg in infants >6 months). The incidences of hypotension using the two definitions were compared.

RESULTS

Awake BP values were obtained in 85% of the patients. Calm patients were more likely to allow their BP to be measured than anxious patients. Anxious patients had higher preinduction MAP values than calm patients. The relative BP approach resulted in a higher incidence of postinduction hypotension than using absolute BP values.

CONCLUSIONS

Awake BP values were unobtainable in 15% of our patients, resulting in the necessity to define hypotension under anesthesia using absolute BP values. Definitions of hypotension using either absolute MAP or values relative to awake baseline are not interchangeable.

Impact of mode of delivery on skin microcirculation in term healthy newborns within the first day of life

BACKGROUND

Microcirculation is an important component of hemodynamic physiology. It can be assessed simply by clinical scores or by a variety of techniques including sidestream dark field (SDF) imaging and peripheral perfusion index (PI) measurements. Mode of delivery may have affects on microcirculation during transitional period. The aim of this study was to compare skin microcirculation in newborns born via vaginal delivery (VD) or cesarian section (C/S).

METHODS

Term healthy newborns not requiring NICU admission were included. Vital signs were recorded. Skin microcirculation was determined by clinical scoring including capillary refill time, skin color, warmth of extremities, by SDF imaging where capillary density and microvascular flow is determined and by PI measurements where pulsatile and nonpulsatile capillary flow is measured. Assessments were done at 30 min and 24 h of life. Results were compared between VD and C/S groups and overtime.

RESULTS

There were 12 newborns in VD group and 25 newborns in C/S group. No difference was observed in microcirculation assessments between groups. However VD group had increased hyperdynamic flow overtime.

CONCLUSION

In healthy term newborns microcirculation does not seem to be affected by mode of delivery, however results may differ in sick or preterm newborns.

Oxygen targeting in preterm infants: a physiological interpretation

Randomized controlled trials evaluating low-target oxygen saturation (SpO2:85% to 89%) vs high-target SpO2 (91% to 95%) have shown variable results regarding mortality and morbidity in extremely preterm infants. Because of the variation inherent to the accuracy of pulse oximeters, the unspecified location of probe placement, the intrinsic relationship between SpO2 and arterial oxygen saturation (SaO2) and between SaO2 and partial pressure of oxygen (PaO2) (differences in oxygen dissociation curves for fetal and adult hemoglobin), the two comparison groups could have been more similar than dissimilar. The SpO2 values were in the target range for a shorter period of time than intended due to practical and methodological constraints. So the studies did not truly compare 'target SpO2 ranges'. In spite of this overlap, some of the studies did find significant differences in mortality prior to discharge, necrotizing enterocolitis and severe retinopathy of prematurity. These differences could potentially be secondary to time spent beyond the target range (SpO2 <85 or >95%) and could be avoided with an intermediate but wider target SpO2 range (87% to 93%). In conclusion, significant uncertainty persists about the desired target range of SpO2 in extremely preterm infants. Further studies should focus on studying newer methods of assessing oxygenation and strategies to limit hypoxemia (<85% SpO2) and hyperoxemia (>95% SpO2).

Microcirculatory mechanisms in postnatal hypotension affecting premature infants

BACKGROUND

Hypotension remains a common complication in preterm infants and is associated with high neonatal morbidity and mortality. The underlying mechanisms are still not fully understood. We studied the microcirculation in extremely low birth weight infants to understand the relationship between blood pressure and skin perfusion.

METHODS

In 21 patients (gestational age <30 wk, birth weight <1,225 g), functional vessel density (FVD) and diameter distribution were obtained prospectively by side stream dark-field imaging at the right arm in the first 48 h after birth. Infants with blood pressure below gestational age and receiving catecholamines were defined as hypotensive as compared with the remaining normotensive control group.

RESULTS

In the first 6 h after birth, FVD was significantly higher in the hypotensive group than in the control group. After 12 h, there were no significant differences in either blood pressure or FVD between the two groups. FVD did not change significantly during the observation period in either group.

CONCLUSION

Hypotensive infants have a higher FVD, possibly due to loss of microvascular tone leading to vasodilation and flow redistribution. However, the link between blood pressure and perfusion remains unclear, and no definitive correlation could be found.

Neonatal hemodynamics: monitoring, data acquisition and analysis

Monitoring of cardiovascular function is critical to both clinical care and research as the use of sophisticated monitoring systems enable us to obtain accurate, reliable and real-time information on developmental hemodynamics in health and disease. Novel approaches to comprehensive hemodynamic monitoring and data acquisition will undoubtedly aid in developing a better understanding of developmental cardiovascular physiology in neonates. In addition, development and use of state-of-the-art, comprehensive hemodynamic monitoring systems enable the recognition of signs of cardiovascular compromise in its early stages, and provide information on the hemodynamic response to treatment in critically ill patients.

The influence of perinatal asphyxia on peripheral oxygenation and perfusion in neonates

BACKGROUND

Perinatal asphyxia influences peripheral oxygenation and perfusion in neonates.

OBJECTIVES

The aim was to investigate the influence of perinatal asphyxia on peripheral oxygenation and perfusion in neonates by using near-infrared spectroscopy (NIRS).

METHODS

Prospective observational study. Neonates with gestational age >34 weeks and birth weight >2000 g without infection or congenital malformations were included. Peripheral muscle NIRS measurements in combination with venous occlusion were performed once in the first 48 h of life. Tissue oxygenation index (TOI), mixed venous oxygenation (SvO2), fractional oxygen extraction (FOE), haemoglobin flow (Hbflow), oxygen delivery (DO2) and oxygen consumption (VO2) were assessed. Furthermore arterial oxygen saturation, heart rate, blood pressure and temperatures were measured. Neonates with a UapH≤7.15 and an Apgar 5≤6 were compared to neonates with a UapH≥7.15, an Apgar 5≥7 (control group) and a UapH was correlated to NIRS parameters.

RESULTS

8 asphyxiated neonates were compared to 30 neonates in the control group. TOI (67.7±5.5%) and DO2 (29.0±14.2 μmol/100 mL/min) were significantly lower in asphyxiated neonates compared to the controls (TOI 71.8±4.9%, p=0.045; DO2 43.9±16.9 μmol/100 mL/min, p=0.028) and FOE was significantly higher (0.33±0.05) compared to the controls (0.28±0.06, p=0.028). Furthermore significant correlations between UapH and DO2 (r=0.78, p=0.022), VO2 (r=0.80, p=0.018) and FOE (r=-0.75, p=0.034) in the asphyxiated group were found.

CONCLUSION

Peripheral oxygenation and perfusion measured with NIRS are compromised in neonates with perinatal asphyxia with worsening of parameters and degree of acidosis in the umbilical cord blood.

Myocardial performance assessment in neonates by one-segment strain and strain rate analysis by tissue Doppler - a quality improvement cohort study

OBJECTIVES

To investigate one-segment strain and strain rate indices as measures of myocardial performance in asphyxiated term neonates.

DESIGN

Quality improvement cohort study.

SETTING

Newborns admitted to a neonatal intensive care unit at a Norwegian University Hospital for perinatal asphyxia and non-asphyxiated newborn recruited from the maternity ward at the same hospital.

PARTICIPANTS

Twenty asphyxiated and 48 non-asphyxiated term neonates.

PRIMARY OUTCOME MEASURE

Strain and strain rate indices and repeatability measures. One-segment longitudinal strain and strain rate by tissue Doppler were assessed on days 1, 2 and 3 of life in nine heart walls. Repeatability was compared against measurements from two-segment analyses previously performed in the same images.

RESULTS

The 95% limits of agreement were significantly better for the one-segment than two-segment repeatability analyses, the inter-rater peak systolic strain (PSS) was (-3.1, 3.3) vs (-11.4, 18.3)%, the inter-rater peak systolic strain rate (PSSR) was (-0.38, 0.40) vs (-0.79, 1.15)/s, the intra-rater PSS was (-2.5, 2.6) vs (-8.0, 9.8)% and the intra-rater PSSR was (-0.23, 0.25) vs (-0.75, 0.80)/s (p<0.05). The myocardial performance was lower in the asphyxiated neonates (indices closer to zero) than in the non-asphyxiated neonates, PSS was -17.8 (0.6) (mean (SEM)) vs -21.2 (0.3)%, PSSR -1.43 (0.08) vs -1.61 (0.03)/s, early diastolic strain rate 1.72 (0.11) vs 2.00 (0.11)/s and strain rate during the atrial systole 1.92 (0.17) vs 2.27 (0.10)/s (p<0.05), despite no difference in fractional shortening (29.0 (0.5) vs 29.1 (1.0)%) (p>0.05).

CONCLUSIONS

One-segment strain and strain rate assessed the reduced myocardial performance in asphyxiated neonates with significantly improved reproducibility as compared with two-segment analysis and was therefore more feasible than two-segment analyses for assessment of myocardial performance after perinatal asphyxia.

Pulmonary hemodynamics and vascular reactivity in asphyxiated term lambs resuscitated with 21 and 100% oxygen

An increase in oxygen tension is an important factor in decreasing pulmonary vascular resistance (PVR) at birth. Birth asphyxia results in acidosis and increased PVR. We determined the effect of resuscitation with 21 vs. 100% O(2) on pulmonary hemodynamics, pulmonary arterial (PA) reactivity, and oxidant stress in a lamb model of in utero asphyxia. Term fetal lambs were acutely asphyxiated by intrauterine umbilical cord occlusion for 10 min resulting in acidosis (pH 6.96 ± 0.05 and Pco(2) 103 ± 5 Torr), bradycardia, systemic hypotension, and increased PVR. Lambs were treated with 30 min of resuscitation with 21% or 100% O(2) (n = 6 each). Pa(O(2)) was significantly elevated with 100% O(2) resuscitation compared with 21% O(2) (430 ± 38 vs. 64 ± 8 Torr), but changes in pH and Pa(CO(2)) were similar. The 100% O(2) induced greater increase in pulmonary blood flow and decrease in PVR at 1 min of life, but subsequent values were similar to 21% O(2) group between 2 and 30 min of life. Oxygen uptake from the lung and systemic oxygen extraction was similar between the two groups. Pulmonary arteries showed increased staining for superoxide anions and increased contractility to norepinephrine following resuscitation with 100% O(2). The increased PA contractility induced by 100% O(2) was reversed by scavenging superoxide anions with superoxide dismutase and catalase. We conclude that resuscitation of asphyxiated lambs with 100% O(2) increases Pa(O(2)) but does not improve lung oxygen uptake, decrease PVR at 30 min, or increase systemic oxygen extraction ratios. Furthermore, 100% O(2) also induces oxidative stress and increases PA contractility. These findings support the new neonatal resuscitation guidelines recommending 21% O(2) for initial resuscitation of asphyxiated neonates.