Dynamic changes in the direction of blood flow through the ductus arteriosus at birth

Antenatal betamethasone augments lung perfusion but lowers upper body blood flow and O2 delivery with delayed cord clamping at birth in preterm lambs

Although the corticosteroid betamethasone is routinely administered to accelerate lung and cardiovascular maturation in the preterm fetus prior to birth, and use of delayed cord clamping (DCC) is recommended at birth by professional bodies, it is unknown whether antenatal betamethasone alters perinatal pulmonary or systemic arterial blood flow accompaniments of DCC. To address this issue, preterm fetal lambs [gestation 127 (1) days, term = 147 days] with (n = 10) or without (n = 10) antenatal betamethasone treatment were acutely instrumented under general anaesthesia with flow probes to obtain left (LV) and right ventricular (RV) outputs, major central arterial blood flows and shunt flow across both the ductus arteriosus and foramen ovale (FO). After delivery, lambs underwent initial ventilation for 2 min prior to DCC. During initial ventilation and after DCC, betamethasone (1) augmented rises in pulmonary arterial blood flow, with this greater increase supported during initial ventilation by enhanced pulmonary distribution of a higher RV output that was largely underpinned by newly emergent and substantial left-to-right (L → R) shunting across the FO, and after DCC, by an added contribution from more pronounced L → R ductal shunting; (2) increased a redistribution of LV output away from the upper body region, accompanied by lowering of upper body blood flow and O2 delivery; and (3) accentuated a progressive systemic-to-pulmonary arterial shift in the distribution of the combined LV and RV output that occurred in conjunction with more pronounced perinatal L → R shunting. These findings suggest that antenatal betamethasone substantially alters arterial blood flow effects of initial ventilation and DCC in the preterm birth transition. KEY POINTS: Betamethasone is given to increase fetal lung and cardiovascular maturation prior to preterm birth, while delayed cord clamping (DCC) is recommended at birth. Whether antenatal betamethasone alters perinatal arterial blood flow responses to DCC is unknown. Anaesthetized preterm fetal lambs with or without betamethasone pretreatment were instrumented with central arterial flow probes and, at birth, underwent ∼2 min of ventilation before DCC. Betamethasone augmented perinatal rises in pulmonary arterial blood flow, related to enhanced pulmonary distribution during initial ventilation of a higher right ventricular output largely underpinned by left-to-right (L → R) shunting across the foramen ovale, with an added contribution from more pronounced L → R ductal shunting after DCC. Betamethasone increased a redistribution of left ventricular output away from the upper body region, with lowering of upper body blood flow and O2 delivery. Betamethasone accentuated a systemic-to-pulmonary arterial shift in the distribution of combined ventricular output occurring with greater perinatal L → R shunting.

The cardiopulmonary benefits of physiologically based cord clamping persist for at least 8 hours in lambs with a diaphragmatic hernia

Introduction

Infants with congenital diaphragmatic hernia can suffer severe respiratory insufficiency and pulmonary hypertension after birth. Aerating the lungs before removing placental support (physiologically based cord clamping, PBCC) increases pulmonary blood flow (PBF) and reduces pulmonary vascular resistance (PVR) in lambs with a diaphragmatic hernia (DH). We hypothesized that these benefits of PBCC persist for at least 8 h after birth.

Methods

At ∼138 days of gestation age (dGA), 21 lambs with a surgically induced left-sided DH (∼86 dGA) were delivered via cesarean section. The umbilical cord was clamped either before ventilation onset (immediate cord clamping, ICC, n = 9) or after achieving a tidal volume of 4 ml/kg, with a maximum delay of 10 min (PBCC, n = 12). The lambs were ventilated for 8 h, initially with conventional mechanical ventilation, but were switched to high-frequency oscillatory ventilation after 30 min if required. Ventilatory parameters, cardiopulmonary physiology, and arterial blood gases were measured throughout the study.

Results

PBF increased after ventilation onset in both groups and was higher in the PBCC DH lambs than the ICC DH lambs at 8 h (5.2 ± 1.2 vs. 1.9 ± 0.3 ml/min/g; p < 0.05). Measured over the entire 8-h ventilation period, PBF was significantly greater (p = 0.003) and PVR was significantly lower (p = 0.0002) in the PBCC DH lambs compared to the ICC DH lambs. A high incidence of pneumothoraces in both the PBCC (58%) and ICC (55%) lambs contributed to a reduced sample size at 8 h (ICC n = 4 and PBCC n = 4).

Conclusion

Compared with ICC, PBCC increased PBF and reduced PVR in DH lambs and the effects were sustained for at least 8 h after ventilation onset.

Outcomes after delivery room positive pressure ventilation in late preterm and term infants

Objectives

Characterize short-term outcomes of late preterm and term infants who received positive pressure ventilation in the delivery room and compare these with infants who did not receive resuscitation at birth.

Study Design

Single center retrospective cohort study of infants born between 35 0/7 and 41 6/7 weeks' gestation in 2019. Baseline characteristics and outcomes of infants who received positive pressure ventilation were compared with controls who did not receive delivery room ventilation. The primary outcome was neonatal intensive care unit admission; secondary outcomes included multiple hospital morbidities and interventions.

Results

Among 202 infants who received delivery room positive pressure ventilation, 77 (38.1%) received ≤1 min, and 125 (61.9%) received >1 min of positive pressure ventilation. Neonatal intensive care unit admission directly following resuscitation was more common in the ventilation cohort (33%) compared with controls (1.5%), p ≤ 0.0001. After initial admission to the newborn nursery, intensive care unit transfer rates were similar in the positive pressure ventilation cohort (4%) and controls (5%). Antibiotic exposure, hypoxic ischemic encephalopathy, respiratory support in the neonatal intensive care unit, and pneumothorax were more common in the ventilation cohort. The composite outcome of any post-delivery complication occurred in 45% of positive pressure ventilation-exposed infants, compared to 15.8% of control infants (<0.0001); this was more common following >1 min (52.8%) than ≤1 min positive pressure ventilation (32.5%), p = 0.002.

Conclusion

Post-delivery complications are common following delivery room positive pressure ventilation, emphasizing the need for post-resuscitation monitoring in either the neonatal intensive care unitor newborn nursery setting.

Deferred cord clamping to improve neonatal blood values: A systematic review and meta-analysis

BACKGROUND

Practices related to umbilical cord clamping at birth should be evidence-based. Deferred cord clamping, compared to immediate cord clamping, shows benefits for preterm neonates but this may also apply to healthy term neonates. Different blood sampling techniques are used to measure effect of deferred and immediate cord clamping.

OBJECTIVE

To assess the statistical and effect size differences between blood biomarkers from umbilical cord and capillary blood samples of healthy term neonates following either immediate or deferred cord clamping.

DESIGN

Systematic review and meta-analysis.

METHODS

The databases PubMed, Medline, CENTRAL, CINAHL and EMBASE were systematically searched. We included studies with a randomised clinical trial design comparing deferred and immediate cord clamping among healthy term neonates born by a spontaneous vaginal birth, reporting on blood biomarkers. Studies including caesarean births and premature births/neonates were excluded. Study attributes, sampling technique, blood biomarkers, mean differences, and standard deviations were extracted. The standardised mean differences (SMD) and sampling errors were calculated for effect size estimation. Meta-analyses were performed if ≥2 studies reported the same outcome using RevMan 5. Subgroup analyses distinguished effects from umbilical cord and capillary blood samples. Moderator tests and publication bias analyses were performed using JASP.

RESULTS

Fifteen studies were included for analysis. The biomarkers haematocrit, haemoglobin, and bilirubin were reported in ≥2 studies and thus eligible for pooling. No differences were found in haemoglobin (SMD -0.04, 95%CI -0.57 to 0.49) or bilirubin values (SMD 0.13, 95%CI -0.03 to 0.28) between umbilical cord blood samples collected after deferred or immediate cord clamping. Deferred cord clamping led to lower haematocrit values (SMD -0.3, 95%CI -0.53 to -0.07). Higher haematocrit (SMD 0.67, 95%CI 0.37 to 0.97) and haemoglobin values (SMD 0.76, 95%CI 0.56 to 0.97) from capillary blood samples, collected 2 to 72 h postpartum, showed when cord clamping was deferred. No effect was found on bilirubin values (SMD 0.13, 95%CI -0.03 to 0.28) irrespective of the sampling technique.

CONCLUSIONS

Blood collected after deferred umbilical cord clamping showed increased haemoglobin and haematocrit values up to 72 h after birth, opposed to bilirubin values. Clinical evaluation of blood biomarkers from the umbilical cord shows different values compared to capillary blood. Sampling time and technique therefore seem essential in estimating the effects of deferred cord clamping.

TWEETABLE ABSTRACT

This meta-analysis shows that sampling time and technique are essential in estimating the effects of deferred cord clamping on neonatal blood values.

Impact of cord clamping on haemodynamic transition in term newborn infants

OBJECTIVE

To assess the haemodynamic consequences of cord clamping (CC) in healthy term infants.

DESIGN

Cohort study.

SETTING

Tertiary maternity hospital.

PATIENTS

46 full-term vigorous infants born by caesarean section.

INTERVENTIONS

Echocardiography was performed before CC, immediately after CC and at 5 min after birth.

MAIN OUTCOME MEASURES

Pulsed wave Doppler-derived cardiac output and the pulmonary artery acceleration time indexed to the right ventricle ejection time were obtained. As markers of loading fluctuations, the myocardial performance indexes and the velocities of the tricuspid and mitral valve annuli were determined with tissue Doppler imaging. Heart rate was derived from Doppler imaging throughout the assessments.

RESULTS

Left ventricular output increased throughout the first minutes after birth (mean (SD) 222.4 (32.5) mL/kg/min before CC vs 239.7 (33.6) mL/kg/min at 5 min, p=0.01), while right ventricular output decreased (306.5 (48.2) mL/kg/min before vs 272.8 (55.5) mL/kg/min immediately after CC, p=0.001). The loading conditions of both ventricles were transiently impaired by CC, recovering at 5 min. Heart rate progressively decreased after birth, following a linear trend temporarily increased by CC. The variation in left ventricular output across the CC was directly correlated to the fluctuation of left ventricular preload over the same period (p=0.03).

CONCLUSIONS

This study illustrates the cardiovascular consequences of CC in term vigorous infants and offers insight into the haemodynamic transition from fetal to neonatal circulation in spontaneously breathing newborns. Strategies that aim to enhance left ventricular preload before CC may prevent complications of perinatal cardiovascular imbalance.

Extended period of ventilation before delayed cord clamping augments left-to-right shunting and decreases systemic perfusion at birth in preterm lambs

Previous studies have suggested that an extended period of ventilation before delayed cord clamping (DCC) augments birth-related rises in pulmonary arterial (PA) blood flow. However, it is unknown whether this greater rise in PA flow is accompanied by increases in left ventricular (LV) output and systemic arterial perfusion or whether it reflects enhanced left-to-right shunting across the ductus arteriosus and/or foramen ovale (FO), with decreased systemic arterial perfusion. Using an established preterm lamb birth transition model, this study compared the effect of a short (∼40 s, n = 11), moderate (∼2 min, n = 11) or extended (∼5 min, n = 12) period of initial mechanical lung ventilation before DCC on flow probe-derived perinatal changes in PA flow, LV output, total systemic arterial blood flow, ductal shunting and FO shunting. The LV output was relatively stable during initial ventilation but increased after DCC, with similar responses in all groups. Systemic arterial flow patterns displayed only minor differences during brief and moderate periods of initial ventilation and were similar after DCC. However, an increase in PA flow was augmented with an extended initial ventilation (P < 0.001), owing to an earlier onset of left-to-right ductal and FO shunting (P < 0.001), and was accompanied by a pronounced reduction in total systemic arterial flow (P = 0.005) that persisted for 4 min after DCC (P ≤ 0.039). These findings suggest that, owing to increased left-to-right shunting and a greater reduction in systemic arterial perfusion, an extended period of ventilation before DCC does not result in greater perinatal circulatory benefits than shorter periods of initial ventilation in the birth transition. KEY POINTS: Previous studies suggest that an extended period of initial ventilation before delayed cord clamping (DCC) augments birth-related rises in pulmonary arterial (PA) blood flow. It is unknown whether this greater rise in PA flow is accompanied by an increased left ventricular output and systemic arterial perfusion or whether it reflects enhanced left-to-right shunting across the ductus arteriosus and/or foramen ovale, with decreased systemic arterial perfusion. Anaesthetized preterm fetal lambs instrumented with central arterial flow probes underwent a brief (∼40 s), moderate (∼2 min) or extended (∼5 min) period of ventilation before DCC. Perinatal changes in left ventricular output were similar in all groups, but extended initial ventilation augmented both perinatal increases in PA flow, owing to earlier onset and greater left-to-right ductal and foramen ovale shunting, and perinatal reductions in total systemic arterial perfusion. Extended ventilation before DCC does not confer a greater perinatal circulatory benefit than shorter periods of initial ventilation.

Surfactant and neonatal hemodynamics during the postnatal transition

Surfactant replacement therapy (SRT) has revolutionized the management of respiratory distress syndrome (RDS) in premature infants, leading to improved survival rates and decreased morbidity. SRT may, however, be associated with hemodynamic changes, which can have both positive and negative effects on the immature cardiovascular system, during the transitional adaptation from fetal to extrauterine environment. However, there is a relative paucity of evidence in this domain, with most of them derived from small heterogeneous observational studies providing conflicting results. In this review, we will discuss the hemodynamic changes that occur with surfactant administration during this vulnerable period, focusing on available evidence regarding changes in pulmonary and systemic blood flow, cerebral circulation and their clinical implications.

Cardiovascular responses to mild perinatal asphyxia in growth-restricted preterm lambs

Growth-restricted neonates have worse outcomes after perinatal asphyxia, with more severe metabolic acidosis than appropriately grown neonates. The cardiovascular physiology associated with fetal growth restriction (FGR) may alter their response to asphyxia. However, research on asphyxia in FGR is limited. Here we compared cardiovascular hemodynamics in preterm FGR and control lambs during mild perinatal asphyxia. We induced FGR in one twin at 89 days gestation (term 148 days), while the other served as a control. At 126 days gestation, lambs were instrumented to allow arterial blood pressure and regional blood flow recording, and then mild perinatal asphyxia was induced by umbilical cord clamping, and resuscitation followed neonatal guidelines. FGR lambs maintained carotid blood flow (CBF) for 7 min, while control lambs rapidly decreased CBF (P < 0.05). Fewer growth-restricted lambs needed chest compressions for return of spontaneous circulation (ROSC) (17 vs. 83%, P = 0.02). The extent of blood pressure overshoot after ROSC was similar, but it took longer for MAP to return to baseline in FGR lambs (18.83 ± 0.00 vs. 47.67 ± 0.00 min, P = 0.003). Growth-restricted lambs had higher CBF after ROSC (P < 0.05) and displayed CBF overshoot, unlike control lambs (P < 0.03). In conclusion, preterm growth-restricted lambs show resilience during perinatal asphyxia based on prolonged CBF maintenance and reduced need for chest compressions during resuscitation. However, CBF overshoot after ROSC may increase the risk of cerebrovascular injury in FGR.NEW & NOTEWORTHY Preterm growth-restricted lambs maintain carotid blood flow for longer than control lambs during asphyxia and have a lower requirement for chest compressions than control lambs during resuscitation. Preterm growth-restricted, but not control, lambs displayed an overshoot in carotid blood flow following return of spontaneous circulation.

Lung aeration reduces blood pressure surges caused by umbilical cord milking in preterm lambs

Background

Umbilical cord milking (UCM) at birth causes surges in arterial blood pressure and blood flow to the brain, which may explain the high risk of intraventricular haemorrhage (IVH) in extremely preterm infants receiving UCM. This high risk of IVH has not been reported in older infants.

Objective

We hypothesized that lung aeration before UCM, reduces the surge in blood pressure and blood flow induced by UCM.

Methods

At 126 days' gestation, fetal lambs (N = 8) were exteriorised, intubated and instrumented to measure umbilical, pulmonary, cerebral blood flows, and arterial pressures. Prior to ventilation onset, the umbilical cord was briefly (2-3 s) occluded (8 times), which was followed by 8 consecutive UCMs when all physiological parameters had returned to baseline. Lambs were then ventilated. After diastolic pulmonary blood flow markedly increased in response to ventilation, the lambs received a further 8 consecutive UCMs. Ovine umbilical cord is shorter than the human umbilical cord, with ∼10 cm available for UCMs. Therefore, 8 UCMs/occlusions were done to match the volume reported in the human studies. Umbilical cord clamping occurred after the final milk.

Results

Both umbilical cord occlusions and UCM caused significant increases in carotid arterial blood flow and pressure. However, the increases in systolic and mean arterial blood pressure (10 ± 3 mmHg vs. 3 ± 2 mmHg, p = 0.01 and 10 ± 4 mmHg vs. 6 ± 2 mmHg, p = 0.048, respectively) and carotid artery blood flow (17 ± 6 ml/min vs. 10 ± 6 ml/min, p = 0.02) were significantly greater when UCM occurred before ventilation onset compared with UCM after ventilation.

Conclusions

UCM after ventilation onset significantly reduces the increases in carotid blood flow and blood pressure caused by UCM.

The role of furosemide and fluid management for a hemodynamically significant patent ductus arteriosus in premature infants

A patent ductus arteriosus (PDA) in infants born premature can present significant management challenges for neonatal providers. Quantifying a hemodynamically significant PDA (hsPDA) represents the first hurdle, however, identifying the best evidence-based approach amongst conservative, pharmacologic, and/or interventional management options has proven to be even more complicated. Within the conservative arm, furosemide to reduce pulmonary edema and improve lung function has spawned several discussions given the concerns for its upregulation of prostaglandin E₂ in the kidneys and conflicting outcomes data. There remains no consensus regarding furosemide use in hsPDAs. In this perspective article, we summarize the approach to defining a hsPDA, review the current practice of furosemide use in the management of hsPDA, and suggest an approach to fluid management and diuresis to address the question: is the routine use of furosemide in hsPDA merited in current practice?

The interplay between pressure, flow, and resistance in neonatal pulmonary hypertension

Pulmonary hypertension, conventionally defined by absolute pulmonary artery pressure, is the result of a range of diagnoses that can result in clinical problems in neonatal practice. Causes include persistent pulmonary hypertension of the newborn, congenital heart disease, and left heart dysfunction, as well as the normally high pulmonary artery resistance in neonates. Elucidating the cause of pulmonary hypertension is vital to guide appropriate management. A first principles approach based on hemodynamic calculations provides a framework for the diagnostic work up and subsequent therapy. Central to this is the equation 'pressure = flow x resistance' and knowledge of factors contributing to flow and resistance and their impact on pulmonary artery pressure. While formal, accurate, calculation of each element is usually not required or deliverable in small infants, clinical and echocardiographic parameters, combined with an understanding of the interplay between pressure, flow, and resistance, significantly improves the assessment and management of neonatal pulmonary hemodynamics.

Resuscitation of Term Compromised and Asphyctic Newborns: Better with Intact Umbilical Cord?

The authors hypothesize that particularly severely compromised and asphyctic term infants in need of resuscitation may benefit from delayed umbilical cord clamping (after several minutes). Although evidence is sparse, the underlying pathophysiological mechanisms support this assumption. For this review the authors have analyzed the available research. Based on these data they conclude that it may be unfavorable to immediately clamp the cord of asphyctic newborns (e.g., after shoulder dystocia) although recommended in current guidelines to provide quick neonatological support. Compression of the umbilical cord or thorax obstructs venous flow to the fetus more than arterial flow to the placenta. The fetus is consequently cut off from a supply of oxygenated, venous blood. This may cause not only hypoxemia and consecutive hypoxia during delivery but possibly also hypovolemia. Immediate cord clamping may aggravate the situation of the already compromised newborn, particularly if the cord is cut before the lungs are ventilated. By contrast, delayed cord clamping leads to fetoplacental transfusion of oxygenated venous blood, which may buffer an existing acidosis. Furthermore, it may enhance blood volume by up to 20%, leading to higher levels of various blood components, such as red and white blood cells, thrombocytes, mesenchymal stem cells, immunoglobulins, and iron. In addition, the resulting increase in pulmonary perfusion may compensate for an existing hypoxemia or hypoxia. Early cord clamping before lung perfusion reduces the preload of the left ventricle and hinders the establishment of sufficient circulation. Animal models and clinical trials support this opinion. The authors raise the question whether it would be better to resuscitate compromised newborns with intact umbilical cords. Obstetric and neonatal teams need to work even closer together to improve neonatal outcomes.

Divergent effects of initial ventilation with delayed cord clamping on systemic and pulmonary arterial flows in the birth transition of preterm lambs

A current view that delayed cord clamping (DCC) results in greater haemodynamic stability at birth than immediate cord clamping (ICC) is based on comparison of DCC vs. ICC followed by an asphyxial (∼2 min) cord clamp-to-ventilation (CC-V) interval. More recent data suggest that relatively minor perinatal differences in heart rate and blood pressure fluctuations exist between DCC and ICC with a non-asphyxial (<45 s) CC-V interval, but it is unknown how ventricular output and central arterial blood flow effects of DCC compare with those of non-asphyxial ICC. Anaesthetized preterm fetal lambs instrumented with flow probes on major central arteries were ventilated for 97 (7) s (mean (SD)) before DCC at birth (n = 10), or underwent ICC 40 (6) s before ventilation (n = 10). Compared to ICC, initial ventilation and DCC was accompanied by (1) redistribution of a similar level of ascending aortic flow away from cephalic arteries and towards the aortic isthmus after ventilation; (2) a lower right ventricular output after cord clamping that was redistributed towards the lungs, thereby maintaining the absolute contribution of this output to a similar increase in pulmonary arterial flow after birth; and (3) a lower descending thoracic aortic flow after birth, related to a more rapid decline in phasic right-to-left ductal flow only partially offset by increased aortic isthmus flow. However, systemic arterial flows were similar between DCC and non-asphyxial ICC within 5 min after birth. These findings suggest that compared to non-asphyxial ICC, initial ventilation with DCC transiently redistributed central arterial flows, resulting in lower perinatal systemic arterial, but not pulmonary arterial, flows. KEY POINTS: A current view that delayed cord clamping (DCC) results in greater haemodynamic stability at birth than immediate cord clamping (ICC) is based on comparison of DCC vs. ICC with an asphyxial (∼2 min) cord clamp-to-ventilation (CC-V) interval. Recent data suggest that relatively minor perinatal differences in heart rate and blood pressure fluctuations exist between DCC and ICC with a non-asphyxial (<45 s) CC-V interval, but how central arterial blood flow effects of DCC compare with those of non-asphyxial ICC is unknown. Anaesthetized preterm fetal lambs instrumented with central arterial flow probes underwent initial ventilation for ∼90 s before DCC at birth, or ICC for ∼40 s before ventilation. Compared to non-asphyxial ICC, initial ventilation with DCC redistributed central blood flows, resulting in lower systemic, but not pulmonary, arterial flows during this period of transition. This flow redistribution was transitory, however, with systemic arterial flows similar between DCC and non-asphyxial ICC within minutes after birth.

Cardiovascular fetal-to-neonatal transition: an in silico model

BACKGROUND

Previous models describing the fetal-to-neonatal transition often lack oxygen saturation levels, homeostatic control mechanisms, phasic hemodynamic signals, or describe the heart with a time-varying elastance model.

METHODS

We incorporated these elements in the adapted CircAdapt model with the one-fiber model for myocardial contraction, to simulate the hemodynamics of the healthy term human fetal circulation and its transition during the first 24 h after birth. The fetal-to-neonatal model was controlled by a time- and event-based script of changes occurring at birth, such as lung aeration and umbilical cord clamping. Model parameters were based on and validated with human and animal data.

RESULTS

The fetal circulation showed low pulmonary blood flow, right ventricular dominance, and inverted mitral and tricuspid flow velocity patterns, as well as high mean ductus venosus flow velocity. The neonatal circulation showed oxygen saturation levels to gradually increase to 98% in the first 15 min after birth as well as temporary left ventricular volume overload.

CONCLUSIONS

Hemodynamics of the term fetus and 24-h-old neonate, as well as the events occurring directly after birth and the transition during the first 24 h after birth, were realistically represented, allowing the model to be used for educational purposes and future research.

IMPACT

With the addition of oxygen saturation levels, homeostatic pressure-flow control mechanisms, and the one-fiber model for myocardial contraction, a new closed-loop cardiovascular model was constructed to give more insight into the healthy term human fetal circulation and its cardiovascular transition during the first 24 h after birth. Extensive validation confirmed that the hemodynamics of the term fetus and the fetal-to-neonatal transition were realistically represented with the model. This well-validated and versatile model can serve as an education as well as a research platform for in silico investigation of fetal-to-neonatal hemodynamic changes under a wide range of physiological and pathophysiological conditions.

Concordance of expert clinicians' interpretations of the newborn's true physiological state

BACKGROUND

Many physiological aspects of the neonatal transition after birth are unobservable because relevant sensors do not yet exist, compromising clinicians' understanding of a neonate's physiological status. Given that a neonate's true physiological state is currently unavailable, we explored the feasibility of using clinicians' degree of concordance as an approximation of the true physiological state.

METHODS

Two phases of structured interviews were conducted. In Phase 1 (N = 8) and Phase 2 (N = 12), we presented neonatal experts with eight graphical trajectories of real newborns' heart rate and oxygen saturation values in the first 10-15 min after birth. We elicited the participants' interpretations of potential underlying physiological conditions that could explain the vital sign patterns.

RESULTS

The global differential diagnosis data for each phase produced the same pattern of results: (1) four trajectories produced a substantial degree of concordance among clinicians (61-80%) and (2) four trajectories produced a strong degree of concordance among clinicians (81-100%).

CONCLUSIONS

It is possible to achieve a strong degree of concordance among neonatal experts' interpretations of newborn trajectories. Thus, using the degree of concordance as an approximation of the neonate's true physiological state in resuscitation after birth may be a promising direction to explore for cognitive aid design.

IMPACT

Differential diagnoses with a good degree of concordance among expert neonatal clinicians could potentially substitute in part for the direct measurement of key physiological and anatomical variables of the neonatal transition, which is currently unavailable. The concordance of clinicians' judgements or inferences with regards to the true physiological state of the newborn during resuscitation after birth has never been explored. The findings provide a crucial first step toward using consensus of neonatal experts' judgements in the design of a cognitive aid to support clinicians' management of the newborns who require resuscitation after birth.

Reducing lung liquid volume in fetal lambs decreases ventricular constraint

BACKGROUND

This study evaluated whether an increased left ventricular (LV) pump function accompanying reduction of lung liquid volume in fetal lambs was related to increased LV preload, augmented LV contractility, or both.

METHODS

Eleven anesthetized preterm fetal lambs (gestation 128 ± 2 days) were instrumented with (1) an LV micromanometer-conductance catheter to obtain LV end-diastolic volume (EDV) and end-diastolic pressure (EDP), the maximal rate of rise of LV pressure (dP/dt_max), LV output, LV stroke work, and LV end-systolic elastance (E_es), a relatively load-independent measure of contractility; (2) an endotracheal tube to measure mean tracheal pressure and to reduce lung liquid volume. LV transmural pressure was calculated as LV EDP minus tracheal pressure.

RESULTS

Reducing lung liquid volume by 16 ± 4 ml kg^-1 (1) augmented LV output (by 16%, P = 0.001) and stroke work (29%, P < 0.001), (2) increased LV EDV (12%, P < 0.001), (3) increased LV transmural pressure (2.2 mmHg, P < 0.001), (4) did not change LV dP/dt_max normalized for EDV (P > 0.7), and (5) decreased LV E_es (20%, P < 0.01).

CONCLUSION

These findings suggest a rise in LV pump function evident after reduction of lung liquid volume in fetal lambs was related to increased LV preload secondary to lessening of external LV constraint, without any associated rise in LV contractility.

IMPACT

This study has shown that reducing the volume of liquid filling the fetal lungs lessens the degree of external constraint on the heart. This lesser constraint permits a rise in left ventricular dimensions and thus greater cardiac filling that leads to increased left ventricular pumping performance. This study has defined a mechanism whereby a reduction in lung liquid volume results in enhanced pumping performance of the fetal heart. These findings suggest that a reduction in lung liquid volume which occurs during the birth transition contributes to increases in left ventricular dimensions and pumping performance known to occur with birth.

Open or closed: Changes in ductus arteriosus flow patterns at birth using 4D flow MRI in newborn piglets

The ductus arteriosus (DA) functionally closes during the transition from fetal to postnatal life because of lung aeration and corresponding cardiovascular changes. The thorough and explicit measurement and visualization of the right and left heart output during this transition has not been previously accomplished. We combined 4D flow MRI (dynamic volumetric blood flow measurements) and T2 relaxometry (oxygen delivery quantification) in surgically instrumented newborn piglets to assess the DA. This was performed in Large White-Landrace-Duroc piglets (n = 34) spanning four age groups: term-9 days, term-3, term+1, and term+5. Subject's DA status was classified using 4D flow: closed DA, forward DA flow, reversed DA flow, and bidirectional DA flow. Over all states, vessel diameters and flows normalized to body weight increased with age (for example in the ascending aorta flow-term-9: 126.6 ± 45.4; term+5: 260.2 ± 80.0 ml/min per kg; p = 0.0005; ascending aorta diameter-term-9: 5.2 ± 0.8; term+5: 7.7 ± 0.4 mm; p = 0.0004). In subjects with reversed DA blood flow there was lower common carotid artery blood flow (forward: 37.5 ± 9.0; reversed: 20.0 ± 7.4 ml/min per kg; p = 0.032). Linear regression revealed that as net DA flow decreases, common carotid artery flow decreases (R2  = 0.32, p = 0.004), and left (R2  = 0.33, p = 0.003) and right (R2  = 0.34, p = 0.003) pulmonary artery flow increases. Bidirectional DA blood flow changed oxygen saturation as determined by MRI between the ascending and descending aorta (ascending aorta: 90.1% ± 8.4%; descending aorta: 75.6% ± 14.2%; p < 0.05). Expanded use of these techniques in preterm animal models will aid in providing new understandings of normal versus abnormal DA transition, as well as to test the effectiveness of related clinical interventions.

Fetal brain growth and risk of postnatal white matter injury in critical congenital heart disease

OBJECTIVE

To test the hypothesis that delayed brain development in fetuses with d-transposition of the great arteries or hypoplastic left heart syndrome heightens their postnatal susceptibility to acquired white matter injury.

METHODS

This is a cohort study across 3 sites. Subjects underwent fetal (third trimester) and neonatal preoperative magnetic resonance imaging of the brain to measure total brain volume as a measure of brain maturity and the presence of acquired white matter injury after birth. White matter injury was categorized as no-mild or moderate-severe based on validated grading criteria. Comparisons were made between the injury groups.

RESULTS

A total of 63 subjects were enrolled (d-transposition of the great arteries: 37; hypoplastic left heart syndrome: 26). White matter injury was present in 32.4% (n = 12) of d-transposition of the great arteries and 34.6% (n = 8) of those with hypoplastic left heart syndrome. Overall total brain volume (taking into account fetal and neonatal scan) was significantly lower in those with postnatal moderate-severe white matter injury compared with no-mild white matter injury after adjusting for age at scan and site in d-transposition of the great arteries (coefficient: 14.8 mL, 95% confidence interval, -28.8 to -0.73, P = .04). The rate of change in total brain volume from fetal to postnatal life did not differ by injury group. In hypoplastic left heart syndrome, no association was noted between overall total brain volume and change in total brain volume with postnatal white matter injury.

CONCLUSIONS

Lower total brain volume beginning in late gestation is associated with increased risk of postnatal moderate-severe white matter injury in d-transposition of the great arteries but not hypoplastic left heart syndrome. Rate of brain growth was not a risk factor for white matter injury. The underlying fetal and perinatal physiology has different implications for postnatal risk of white matter injury.

Plasma Leak From the Circulation Contributes to Poor Outcomes for Preterm Infants: A Working Hypothesis

Preterm infants are at high risk of death and disability resulting from brain injury. Impaired cardiovascular function leading to poor cerebral oxygenation is a significant contributor to these adverse outcomes, but current therapeutic approaches have failed to improve outcome. We have re-examined existing evidence regarding hypovolemia and have concluded that in the preterm infant loss of plasma from the circulation results in hypovolemia; and that this is a significant driver of cardiovascular instability and thus poor cerebral oxygenation. High capillary permeability, altered hydrostatic and oncotic pressure gradients, and reduced lymphatic return all combine to increase net loss of plasma from the circulation at the capillary. Evidence is presented that early hypovolemia occurs in preterm infants, and that capillary permeability and pressure gradients all change in a way that promotes rapid plasma loss at the capillary. Impaired lymph flow, inflammation and some current treatment strategies may further exacerbate this plasma loss. A framework for testing this hypothesis is presented. Understanding these mechanisms opens the way to novel treatment strategies to support cardiovascular function and cerebral oxygenation, to replace current therapies, which have been shown not to change outcomes.

Brain Volumes in Mice are Smaller at Birth After Term or Preterm Cesarean Section Delivery

The rate of cesarean section (CS) delivery has steadily increased over the past decades despite epidemiological studies reporting higher risks of neonatal morbidity and neurodevelopmental disorders. Yet, little is known about the immediate impact of CS birth on the brain, hence the need of experimental studies to evaluate brain parameters following this mode of delivery. Using the solvent clearing method iDISCO and 3D imaging technique, we report that on the day of birth, whole-brain, hippocampus, and striatum volumes are reduced in CS-delivered as compared to vaginally-born mice, with a stronger effect observed in preterm CS pups. These results stress the impact of CS delivery, at term or preterm, during parturition and at birth. In contrast, cellular activity and apoptosis are reduced in mice born by CS preterm but not term, suggesting that these early-life processes are only impacted by the combination of preterm birth and CS delivery.

Characteristics and physiological basis of falls in ventricular outputs after immediate cord clamping at delivery in preterm fetal lambs

KEY POINTS

Controversy exists about the physiological mechanism(s) underlying decreases in cardiac output after immediate clamping of the umbilical cord at birth. To define these mechanisms, the four major determinants of ventricular output (afterload, preload, heart rate and contractility) were measured concurrently in fetal lambs at 15 s intervals over a 2 min period after cord clamping and before ventilation following delivery. After cord clamping, right (but not left) ventricular output fell by 20% in the initial 30 s, due to increased afterload associated with higher arterial blood pressures, but both outputs then halved over 45 s, due to a falling heart rate and deteriorating ventricular contractility accompanying rapid declines in arterial oxygenation to asphyxial levels. Ventricular outputs subsequently plateaued from 75 to 120 s, associated with rebound rises in ventricular contractility accompanying asphyxia-induced surges in circulating catecholamines. These findings provide a physiological basis for the clinical recommendation that effective ventilation should occur within 60 s after immediate cord clamping.

ABSTRACT

Controversy exists about the physiological mechanism(s) underlying large decreases in cardiac output after immediate clamping of the umbilical cord at birth. To define these mechanisms, anaesthetized preterm fetal lambs (127(1)d, n = 12) were instrumented with flow probes and catheters in major central arteries, and a left ventricular (LV) micromanometer-conductance catheter. Following immediate cord clamping at delivery, haemodynamics, LV and right ventricular (RV) outputs, and LV contractility were measured at 15 s intervals during a 2 min non-ventilatory period, with aortic blood gases and circulating catecholamine (noradrenaline and adrenaline) concentrations measured at 30 s intervals. After cord clamping, (1) RV (but not LV) output fell by 20% in the initial 30 s, due to a reduced stroke volume associated with increased arterial blood pressures, (2) both outputs then halved over the next 45 s, associated with falls in heart rate, arterial blood pressures and ventricular contractility accompanying a rapid decline in arterial oxygenation to asphyxial levels, (3) reduced outputs subsequently plateaued from 75 to 120 s, associated with rebound rises in blood pressures and ventricular contractility accompanying exponential surges in circulating catecholamines. These findings are consistent with a time-dependent decline of ventricular outputs after immediate cord clamping, which comprised (1) an initial, minor fall in RV output related to altered loading conditions, (2) ensuing large decreases in both LV and RV outputs related to the combination of bradycardia and ventricular dysfunction during emergence of an asphyxial state, and (3) subsequent stabilization of reduced LV and RV outputs during ongoing asphyxia, supported by cardiovascular stimulatory effects of marked sympathoadrenal activation.

Effect of maternal oxytocin on umbilical venous and arterial blood flows during physiological-based cord clamping in preterm lambs

BACKGROUND

Delayed umbilical cord clamping (UCC) after birth is thought to cause placental to infant blood transfusion, but the mechanisms are unknown. It has been suggested that uterine contractions force blood out of the placenta and into the infant during delayed cord clamping. We have investigated the effect of uterine contractions, induced by maternal oxytocin administration, on umbilical artery (UA) and venous (UV) blood flows before and after ventilation onset to determine whether uterine contractions cause placental transfusion in preterm lambs.

METHODS AND FINDINGS

At ~128 days of gestation, UA and UV blood flows, pulmonary arterial blood flow (PBF) and carotid arterial (CA) pressures and blood flows were measured in three groups of fetal sheep during delayed UCC; maternal oxytocin following mifepristone, mifepristone alone, and saline controls. Each successive uterine contraction significantly (p<0.05) decreased UV (26.2±6.0 to 14.1±4.5 mL.min-1.kg-1) and UA (41.2±6.3 to 20.7 ± 4.0 mL.min-1.kg-1) flows and increased CA pressure and flow (47.1±3.4 to 52.8±3.5 mmHg and 29.4±2.6 to 37.3±3.4 mL.min-1.kg-1). These flows and pressures were partially restored between contractions, but did not return to pre-oxytocin administration levels. Ventilation onset during DCC increased the effects of uterine contractions on UA and UV flows, with retrograde UA flow (away from the placenta) commonly occurring during diastole.

CONCLUSIONS

We found no evidence that amplification of uterine contractions with oxytocin increase placental transfusion during DCC. Instead they decreased both UA and UV flow and caused a net loss of blood from the lamb. Uterine contractions did, however, have significant cardiovascular effects and reduced systemic and cerebral oxygenation.

Efficacy of Intact Cord Resuscitation Compared to Immediate Cord Clamping on Cardiorespiratory Adaptation at Birth in Infants with Isolated Congenital Diaphragmatic Hernia (CHIC)

Resuscitation at birth of infants with Congenital Diaphragmatic Hernia (CDH) remains highly challenging because of severe failure of cardiorespiratory adaptation at birth. Usually, the umbilical cord is clamped immediately after birth. Delaying cord clamping while the resuscitation maneuvers are started may: (1) facilitate blood transfer from placenta to baby to augment circulatory blood volume; (2) avoid loss of venous return and decrease in left ventricle filling caused by immediate cord clamping; (3) prevent initial hypoxemia because of sustained uteroplacental gas exchange after birth when the cord is intact. The aim of this trial is to evaluate the efficacy of intact cord resuscitation compared to immediate cord clamping on cardiorespiratory adaptation at birth in infants with isolated CDH. The Congenital Hernia Intact Cord (CHIC) trial is a prospective multicenter open-label randomized controlled trial in two balanced parallel groups. Participants are randomized either immediate cord clamping (the cord will be clamped within the first 15 s after birth) or to intact cord resuscitation group (umbilical cord will be kept intact during the first part of the resuscitation). The primary end-point is the number of infants with APGAR score <4 at 1 min or <7 at 5 min. One hundred eighty participants are expected for this trial. To our knowledge, CHIC is the first study randomized controlled trial evaluating intact cord resuscitation on newborn infant with congenital diaphragmatic hernia. Better cardiorespiratory adaptation is expected when the resuscitation maneuvers are started while the cord is still connected to the placenta.

Changes in Umbilico-Placental Circulation during Prolonged Intact Cord Resuscitation in a Lamb Model

Some previous studies reported a benefit to cardiopulmonary transition at birth when starting resuscitation maneuvers while the cord was still intact for a short period of time. However, the best timing for umbilical cord clamping in this condition is unknown. The aim of this study was to explore the duration of effective umbilico-placental circulation able to promote cardiorespiratory adaptation at birth during intact cord resuscitation. Umbilico-placental blood flow and vascular resistances were measured in an experimental neonatal lamb model. After a C-section delivery, the lambs were resuscitated ventilated for 1 h while the cord was intact. The maximum and mean umbilico-placental blood flow were respectively 230 ± 75 and 160 ± 12 mL·min^-1 during the 1 h course of the experiment. However, umbilico-placental blood flow decreased and vascular resistance increased significantly 40 min after birth (p < 0.05). These results suggest that significant cardiorespiratory support can be provided by sustained placental circulation for at least 1 h during intact cord resuscitation.

Neurodevelopmental outcomes of a randomised trial of intact cord resuscitation

AIM

It has been suggested that intact cord resuscitation can reduce the risk of brain damage. We investigated the effects on neurodevelopment at two years of age.

METHODS

This study was performed in Kathmandu, Nepal. In 2016, 231 late preterm and term infants born vaginally and not breathing were randomised to resuscitation with an intact cord or the standard practice of early cord clamping (CC). At two years of age, the World Health Organization's Infant and Young Child Development tool was used to assess the child's neurodevelopment, during telephone interviews with caregivers.

RESULTS

We followed up 138 infants (59.7%) at a mean age of 24.8 ± 0.8 months. A significant difference was seen in the development for age Z-score, between the group resuscitated with an intact umbilical cord and the group resuscitated with early CC. The median (range) scores were 1.0 (0.1-2.1) vs 0.9 (-2.0 to 1.8), respectively (P = .04). There was no difference in the motor, language-cognitive and socio-emotional domains.

CONCLUSION

Neurodevelopment improvements were observed at two years of age in infants resuscitated with an intact rather than early clamped umbilical cord. No definitive conclusions could be drawn due to protocol violations and a low follow-up rate. More research is needed.

Impact of stimulation among non-crying neonates with intact cord versus clamped cord on birth outcomes: observation study

BACKGROUND

Stimulation of non-crying neonates after birth can help transition to spontaneous breathing. In this study, we aim to assess the impact of intact versus clamped umbilical cord on spontaneous breathing after stimulation of non-crying neonates.

METHODS

This is an observational study among non-crying neonates (n=3073) born in hospitals of Nepal. Non-crying neonates born vaginally at gestational age ≥34 weeks were observed for their response to stimulation with the cord intact or clamped. Obstetric characteristics of the neonates were analysed. Association of spontaneous breathing with cord management was assessed using logistic regression.

RESULTS

Among non-crying neonates, 2563 received stimulation. Of these, a higher proportion of the neonates were breathing in the group with cord intact as compared with the group cord clamped (81.1% vs 68.9%, p<0.0001). The use of bag-and-mask ventilation was lower among those who were stimulated with the cord intact than those who were stimulated with cord clamped (18.0% vs 32.4%, p<0.0001). The proportion of neonates with Apgar Score ≤3 at 1 min was lower with the cord intact than with cord clamped (7.6% vs 11.5%, p=0.001). In multivariate analysis, neonates with intact cord had 84% increased odds of spontaneous breathing (adjusted OR, 1.84; 95% CI: 1.48 to 2.29) compared with those with cord clamped.

CONCLUSIONS

Stimulation of non-crying neonates with intact cord was associated with more spontaneous breathing than among infants who were stimulated with cord clamped. Intact cord stimulation may help establish spontaneous breathing in apnoeic neonates, but residual confounding variables may be contributing to the findings. This study provides evidence for further controlled research to evaluate the effect of initial steps of resuscitation with cord intact.

Ductal Flow Ratio as Measure of Transition in Preterm Infants After Birth: A Pilot Study

Background: Cardiovascular changes during the transition from intra- to extrauterine life, alters the pressure gradient across the ductus arteriosus (DA). DA flow ratio (R-L/L-R) has been suggested to reflect the infant's transitional status and could potentially predict neonatal outcomes after preterm birth. Aim: Determine whether DA flow ratio correlates with oxygenation parameters in preterm infants at 1 h after birth. Methods: Echocardiography was performed in preterm infants born <32 weeks gestational age (GA), as part of an ancillary study. DA flow was measured at 1 h after birth. DA flow ratio was correlated with FiO₂, SpO₂, and SpO₂/FiO₂ (SF) ratio. The DA flow ratio of infants receiving physiological-based cord clamping (PBCC) or time-based cord clamping (TBCC) were compared. Results: Measurements from 16 infants were analysed (median [IQR] GA 29 [27-30] weeks; birthweight 1,176 [951-1,409] grams). R-L DA shunting was 16 [17-27] ml/kg/min and L-R was 110 [81-124] ml/kg/min. The DA flow ratio was 0.18 [0.11-0.28], SpO₂ 94 [93-96]%, FiO₂ was 23 [21-28]% and SF ratio 4.1 [3.3-4.5]. There was a moderate correlation between DA flow ratio and SpO₂ [correlation coefficient (CC) -0.415; p = 0.110], FiO₂ (CC 0.384; p = 0.142) and SF ratio (CC -0.356; p = 0.175). There were no differences in DA flow measurements between infants where PBBC or TBCC was performed. Conclusion: In this pilot study we observed a non-significant positive correlation between DA flow ratio at 1 h after birth and oxygenation parameters in preterm infants.

Cerebral Oxygen Changes in Neonates During Immediate Transition After Birth and Early Life: An Observational Study

Purpose

The physiologic transition from a fetus to a neonate is composed of a series of complex processes that include changes in cerebral tissue oxygenation saturation (cSO₂). Monitoring this process is of great importance. This study aimed to define the cSO₂ reference interval in neonates without medical support, extending the measurements until 1 hour after birth, and to determine the incidence of abnormally low or high regional cerebral oxygenation during the neonatal transition.

Patients and Methods

A total of 418 neonates delivered by cesarean section were enrolled. Near-infrared spectroscopy was used to monitor cerebral oxygenation.

Results

We found that cSO₂ of the non-oxygen-inhaled intrathecal anesthesia in neonates without medical support increased from about 49.0% in the second minute. Most of them reached cSO₂ relative stabilization at 55.7-81.0% between 7 and 8 minutes after birth. One hour after birth, newborn cSO₂ was maintained at 78.0-87.0%. The low cSO₂ rate among babies born under intrathecal anesthesia with and without maternal oxygen inhalation during cesarean sections was approximately 4.5% and 9.0%, respectively.

Conclusion

We reported the trend in cSO₂ from 2 minutes after birth to 1 hour in the neonatal nursing room and determined the incidence of abnormal regional cSO₂ during this neonatal transition period. Anesthesiologists should pay special attention to the risk of cSO₂ abnormalities in newborns when managing pregnant women with comorbidities.

Cardiopulmonary Resuscitation of Asystolic Newborn Lambs Prior to Umbilical Cord Clamping; the Timing of Cord Clamping Matters!

Background: Current guidelines recommend immediate umbilical cord clamping (UCC) for newborns requiring chest compressions (CCs). Physiological-based cord clamping (PBCC), defined as delaying UCC until after lung aeration, has advantages over immediate UCC in mildly asphyxiated newborns, but its efficacy in asystolic newborns requiring CC is unknown. The aim of this study was to compare the cardiovascular response to CCs given prior to or after UCC in asystolic near-term lambs.

Methods: Umbilical, carotid, pulmonary, and femoral arterial flows and pressures as well as systemic and cerebral oxygenation were measured in near-term sheep fetuses [139 ± 2 (SD) days gestation]. Fetal asphyxia was induced until asystole ensued, whereupon lambs received ventilation and CC before (PBCC; n = 16) or after (n = 12) UCC. Epinephrine was administered 1 min after ventilation onset and in 3-min intervals thereafter. The PBCC group was further separated into UCC at either 1 min (PBCC₁, n = 8) or 10 min (PBCC₁₀, n = 8) after return of spontaneous circulation (ROSC). Lambs were maintained for a further 30 min after ROSC.

Results: The duration of CCs received and number of epinephrine doses required to obtain ROSC were similar between groups. After ROSC, we found no physiological benefits if UCC was delayed for 1 min compared to immediate cord clamping (ICC). However, if UCC was delayed for 10 min after ROSC, we found significant reductions in post-asphyxial rebound hypertension, cerebral blood flow, and cerebral oxygenation. The prevention of the post-asphyxial rebound hypertension in the PBCC₁₀ group occurred due to the contribution of the placental circulation to a low peripheral resistance. As a result, left and right ventricular outputs continued to perfuse the placenta and were evidenced by reduced mean pulmonary blood flow, persistence of right-to-left shunting across the ductus arteriosus, and persistence of umbilical arterial and venous blood flows.

Conclusion: It is possible to obtain ROSC after CC while the umbilical cord remains intact. There were no adverse effects of PBCC compared to ICC; however, the physiological changes observed after ROSC in the ICC and early PBCC groups may result in additional cerebral injury. Prolonging UCC after ROSC may provide significant physiological benefits that may reduce the risk of harm to the cerebral circulation.

Not Crying After Birth as a Predictor of Not Breathing

BACKGROUND

Worldwide, every year, 6 to 10 million infants require resuscitation at birth according to estimates based on limited data regarding "nonbreathing" infants. In this article, we aim to describe the incidence of "noncrying" and nonbreathing infants after birth, the need for basic resuscitation with bag-and-mask ventilation, and death before discharge.

METHODS

We conducted an observational study of 19 977 infants in 4 hospitals in Nepal. We analyzed the incidence of noncrying or nonbreathing infants after birth. The sensitivity of noncrying infants with nonbreathing after birth was analyzed, and the risk of predischarge mortality between the 2 groups was calculated.

RESULTS

The incidence of noncrying infants immediately after birth was 11.1%, and the incidence of noncrying and nonbreathing infants was 5.2%. Noncrying after birth had 100% sensitivity for nonbreathing infants after birth. Among the "noncrying but breathing" infants, 9.5% of infants did not breathe at 1 minute and 2% did not to breathe at 5 minutes. Noncrying but breathing infants after birth had almost 12-fold odds of predischarge mortality (adjusted odds ratio 12.3; 95% confidence interval, 5.8-26.1).

CONCLUSIONS

All nonbreathing infants after birth do not cry at birth. A proportion of noncrying but breathing infants at birth are not breathing by 1 and 5 minutes and have a risk for predischarge mortality. With this study, we provide evidence of an association between noncrying and nonbreathing. This study revealed that noncrying but breathing infants require additional care. We suggest noncrying as a clinical sign for initiating resuscitation and a possible denominator for measuring coverage of resuscitation.

Brief asphyxial state following immediate cord clamping accelerates onset of left-to-right shunting across the ductus arteriosus after birth in preterm lambs

Reversal of shunting across the ductus arteriosus from right-to-left to left-to-right is a characteristic feature of the birth transition. Given that immediate cord clamping (ICC) followed by an asphyxial cord clamp-to-ventilation (CC-V) interval may augment left ventricular (LV) output and central blood flows after birth, we tested the hypothesis that an asphyxial CC-V interval accelerates the onset of postnatal left-to-right ductal shunting. High-fidelity central blood flow signals were obtained in anesthetized preterm lambs (gestation 128 ± 2 days) after ICC followed by a nonasphyxial (∼40 s, n = 9) or asphyxial (∼90 s, n = 9) CC-V interval before mechanical ventilation for 30 min after birth. Left-to-right ductal flow segments were related to aortic isthmus and descending aortic flow profiles to quantify sources of ductal shunting. In the nonasphyxial group, phasic left-to-right ductal shunting was initially minor after birth, but then rose progressively to 437 ± 164 ml/min by 15 min (P < 0.001). However, in the asphyxial group, this shunting increased from 24 ± 21 to 199 ± 93 ml/min by 15 s after birth (P < 0.001) and rose further to 471 ± 190 ml/min by 2 min (P < 0.001). This earlier onset of left-to-right ductal shunting was supported by larger contributions (P < 0.001) from direct systolic LV flow and retrograde diastolic discharge from an arterial reservoir/windkessel located in the descending aorta and its major branches, and associated with increased pulmonary arterial blood flow having a larger ductal component. These findings suggest that the duration of the CC-V interval after ICC is an important modulator of left-to-right ductal shunting, LV output and pulmonary perfusion at birth.NEW & NOTEWORTHY This birth transition study in preterm lambs demonstrated that a brief (∼90 s) asphyxial interval between umbilical cord clamping and ventilation onset resulted in earlier and greater left-to-right shunting across the ductus arteriosus after birth. This greater shunting 1) resulted from an increased left ventricular output associated with a higher systolic left-to-right ductal flow and increased retrograde diastolic discharge from a lower body arterial reservoir/windkessel, and 2) was accompanied by greater lung perfusion after birth.

Persistent Pulmonary Hypertension of the Newborn: Pathophysiological Mechanisms and Novel Therapeutic Approaches

Persistent pulmonary hypertension of the newborn (PPHN) is one of the main causes of neonatal morbidity and mortality. It is characterized by sustained elevation of pulmonary vascular resistance (PVR), preventing an increase in pulmonary blood flow after birth. The affected neonates fail to establish blood oxygenation, precipitating severe respiratory distress, hypoxemia, and eventually death. Inhaled nitric oxide (iNO), the only approved pulmonary vasodilator for PPHN, constitutes, alongside supportive therapy, the basis of its treatment. However, nearly 40% of infants are iNO resistant. The cornerstones of increased PVR in PPHN are pulmonary vasoconstriction and vascular remodeling. A better understanding of PPHN pathophysiology may enlighten targeted and more effective therapies. Sildenafil, prostaglandins, milrinone, and bosentan, acting as vasodilators, besides glucocorticoids, playing a role on reducing inflammation, have all shown potential beneficial effects on newborns with PPHN. Furthermore, experimental evidence in PPHN animal models supports prospective use of emergent therapies, such as soluble guanylyl cyclase (sGC) activators/stimulators, l-citrulline, Rho-kinase inhibitors, peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists, recombinant superoxide dismutase (rhSOD), tetrahydrobiopterin (BH4) analogs, ω-3 long-chain polyunsaturated fatty acids (LC-PUFAs), 5-HT2A receptor antagonists, and recombinant human vascular endothelial growth factor (rhVEGF). This review focuses on current knowledge on alternative and novel pathways involved in PPHN pathogenesis, as well as recent progress regarding experimental and clinical evidence on potential therapeutic approaches for PPHN.

Effect of spontaneous breathing on umbilical venous blood flow and placental transfusion during delayed cord clamping in preterm lambs

INTRODUCTION

During delayed umbilical cord clamping, the factors underpinning placental transfusion remain unknown. We hypothesised that reductions in thoracic pressure during inspiration would enhance placental transfusion in spontaneously breathing preterm lambs.

OBJECTIVE

Investigate the effect of spontaneous breathing on umbilical venous flow and body weight in preterm lambs.

METHODS

Pregnant sheep were instrumented at 132-133 days gestational age to measure fetal common umbilical venous, pulmonary and cerebral blood flows as well as arterial and intrapleural (IP) pressures. At delivery, doxapram and caffeine were administered to promote breathing. Lamb body weights were measured continuously and breathing was assessed by IP pressure changes.

RESULTS

In 6 lambs, 491 out of 1117 breaths were analysed for change in body weight. Weight increased in 46.6% and decreased in 47.5% of breaths. An overall mean increase of 0.02±2.5 g per breath was calculated, and no net placental transfusion was observed prior to cord clamping (median difference in body weight 52.3 [-54.9-166.1] g, p=0.418). Umbilical venous (UV) flow transiently decreased with each inspiration, and in some cases ceased, before UV flow normalised during expiration. The reduction in UV flow was positively correlated with the standardised reduction in (IP) pressure, increasing by 109 mL/min for every SD reduction in IP pressure. Thus, the reduction in UV flow was closely related to inspiratory depth.

CONCLUSIONS

Spontaneous breathing had no net effect on body weight in preterm lambs at birth. UV blood flow decreased as inspiratory effort increased, possibly due to constriction of the inferior vena cava caused by diaphragmatic contraction, as previously observed in human fetuses.

Physiologically based cord clamping improves cardiopulmonary haemodynamics in lambs with a diaphragmatic hernia

OBJECTIVE

Lung hypoplasia associated with congenital diaphragmatic hernia (CDH) results in respiratory insufficiency and pulmonary hypertension after birth. We have investigated whether aerating the lung before removing placental support (physiologically based cord clamping (PBCC)), improves the cardiopulmonary transition in lambs with a CDH.

METHODS

At ≈138 days of gestational age, 17 lambs with surgically induced left-sided diaphragmatic hernia (≈d80) were delivered via caesarean section. The umbilical cord was clamped either immediately prior to ventilation onset (immediate cord clamping (ICC); n=6) or after achieving a target tidal volume of 4 mL/kg, with a maximum delay of 10 min (PBCC; n=11). Lambs were ventilated for 120 min and physiological changes recorded.

RESULTS

Pulmonary blood flow (PBF) increased following ventilation onset in both groups, but was 19-fold greater in PBCC compared with ICC lambs at cord clamping (19±6.3 vs 1.0±0.5 mL/min/kg, p<0.001). Cerebral tissue oxygenation was higher in PBCC than ICC lambs during the first 10 min after cord clamping (59%±4% vs 30%±5%, p<0.001). PBF was threefold higher (23±4 vs 8±2 mL/min/kg, p=0.01) and pulmonary vascular resistance (PVR) was threefold lower (0.6±0.1 vs 2.2±0.6 mm Hg/(mL/min), p<0.001) in PBCC lambs compared with ICC lambs at 120 min after ventilation onset.

CONCLUSIONS

Compared with ICC, PBCC prevented the severe asphyxia immediately after birth and resulted in a higher PBF due to a lower PVR, which persisted for at least 120 min after birth in CDH lambs.

Issues in cardiopulmonary transition at birth

The transition from fetal to newborn life involves a complex series of physiological events that commences with lung aeration, which is thought to involve 3 mechanisms. Two mechanisms occur during labour, Na⁺ reabsorption and fetal postural changes, and one occurs after birth due to pressure gradients generated by inspiration. However, only one of these mechanisms, fetal postural changes, involves the loss of liquid from the respiratory system. Both other mechanisms involve liquid being reabsorbed from the airways into lung tissue. While this stimulates an increase in pulmonary blood flow (PBF), in large quantities this liquid can adversely affect postnatal respiratory function. The increase in PBF (i) facilitates the onset of pulmonary gas exchange and (ii) allows pulmonary venous return to take over the role of providing preload for the left ventricle, a role played by umbilical venous return during fetal life. Thus, aerating the lung and increasing PBF before umbilical cord clamping (known as physiological based cord clamping), can avoid the loss of preload and reduction in cardiac output that normally accompanies immediate cord clamping.

Neonatal cardiopulmonary transition in an ovine model of congenital diaphragmatic hernia

OBJECTIVE

Infants with a congenital diaphragmatic hernia (CDH) are at high risk of developing pulmonary hypertension after birth, but little is known of their physiological transition at birth. We aimed to characterise the changes in cardiopulmonary physiology during the neonatal transition in an ovine model of CDH.

METHODS

A diaphragmatic hernia (DH) was surgically created at 80 days of gestational age (dGA) in 10 fetuses, whereas controls underwent sham surgery (n=6). At 138 dGA, lambs were delivered via caesarean section and ventilated for 2 hours. Physiological and ventilation parameters were continuously recorded, and arterial blood gas values were measured.

RESULTS

DH lambs had lower wet lung-to-body-weight ratio (0.016±0.002vs0.033±0.004), reduced dynamic lung compliance (0.4±0.1mL/cmH₂O vs1.2±0.1 mL/cmH₂O) and reduced arterial pH (7.11±0.05vs7.26±0.05), compared with controls. While measured pulmonary blood flow (PBF) was lower in DH lambs, after correction for lung weight, PBF was not different between groups (4.05±0.60mL/min/gvs4.29±0.57 mL/min/g). Cerebral tissue oxygen saturation was lower in DH compared with control lambs (55.7±3.5vs67.7%±3.9%).

CONCLUSIONS

Immediately after birth, DH lambs have small, non-compliant lungs, respiratory acidosis and poor cerebral oxygenation that reflects the clinical phenotype of human CDH. PBF (indexed to lung weight) was similar in DH and control lambs, suggesting that the reduction in PBF associated with CDH is proportional to the degree of lung hypoplasia during the neonatal cardiopulmonary transition.

Blunted sympathoadrenal activation accompanies hemodynamic stability after early ventilation and delayed cord clamping at birth in preterm lambs

BACKGROUND

As surges in circulating norepinephrine and epinephrine have chronotropic, pressor, and inotropic effects, we tested the hypothesis that blunted rises in these catecholamines during preterm birth accompanied hemodynamic stability observed after early ventilation and delayed cord clamping (DCC), with findings compared to immediate cord clamping (ICC) and a non-asphyxial cord clamp-to-ventilation interval.

METHODS

Anesthetized preterm fetal lambs were instrumented with arterial micromanometers to obtain pressure and the maximal rate of pressure rise (dP/dt_max) as a surrogate of ventricular contractility and an aortic catheter to obtain blood samples for catecholamine assay. Fetuses were delivered and mechanically ventilated before cord clamping ∼1.5 min later (DCC, n = 9) or subjected to ICC with ventilation started ∼40 s later (n = 8).

RESULTS

Perinatal hemodynamics were stable after DCC, with greater fluctuations evident following birth after ICC (P ≤ 0.05). With DCC, circulating norepinephrine and epinephrine were unchanged after early ventilation but rose following cord clamping (P ≤ 0.01), with concentrations below the threshold for hemodynamic effects. Norepinephrine was higher in the ICC group after cord clamping and immediately after ventilation (P < 0.025), but catecholamine levels were otherwise similar between groups.

CONCLUSION

Hemodynamic stability at birth after DCC is accompanied by sub-threshold rises in circulating norepinephrine and epinephrine and thus blunted sympathoadrenal activation.

Early prediction of spontaneous Patent Ductus Arteriosus (PDA) closure and PDA-associated outcomes: a prospective cohort investigation

BACKGROUND

Patent ductus arteriosus (PDA), the most commonly diagnosed cardiovascular condition in preterm infants, is associated with increased mortality and harmful long-term outcomes (chronic lung disease, neurodevelopmental delay). Although pharmacologic and/or interventional treatments to close PDA likely benefit some infants, widespread routine treatment of all preterm infants with PDA may not improve outcomes. Most PDAs close spontaneously by 44-weeks postmenstrual age; treatment is increasingly controversial, varying markedly between institutions and providers. Because treatment detriments may outweigh benefits, especially in infants destined for early, spontaneous PDA closure, the relevant unanswered clinical question is not whether to treat all preterm infants with PDA, but whom to treat (and when). Clinicians cannot currently predict in the first month which infants are at highest risk for persistent PDA, nor which combination of clinical risk factors, echocardiographic measurements, and biomarkers best predict PDA-associated harm.

METHODS

Prospective cohort of untreated infants with PDA (n=450) will be used to predict spontaneous ductal closure timing. Clinical measures, serum (brain natriuretic peptide, N-terminal pro-brain natriuretic peptide) and urine (neutrophil gelatinase-associated lipocalin, heart-type fatty acid-binding protein) biomarkers, and echocardiographic variables collected during each of first 4 postnatal weeks will be analyzed to identify those associated with long-term impairment. Myocardial deformation imaging and tissue Doppler imaging, innovative echocardiographic techniques, will facilitate quantitative evaluation of myocardial performance. Aim1 will estimate probability of spontaneous PDA closure and predict timing of ductal closure using echocardiographic, biomarker, and clinical predictors. Aim2 will specify which echocardiographic predictors and biomarkers are associated with mortality and respiratory illness severity at 36-weeks postmenstrual age. Aim3 will identify which echocardiographic predictors and biomarkers are associated with 22 to 26-month neurodevelopmental delay. Models will be validated in a separate cohort of infants (n=225) enrolled subsequent to primary study cohort.

DISCUSSION

The current study will make significant contributions to scientific knowledge and effective PDA management. Study results will reduce unnecessary and harmful overtreatment of infants with a high probability of early spontaneous PDA closure and facilitate development of outcomes-focused trials to examine effectiveness of PDA closure in "high-risk" infants most likely to receive benefit.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03782610. Registered 20 December 2018.

Physiological-based cord clamping in preterm infants using a new purpose-built resuscitation table: a feasibility study

OBJECTIVE

Physiological-based cord clamping (PBCC) led to a more stable cardiovascular adaptation and better oxygenation in preterm lambs, but in preterm infants, this approach has been challenging. Our aim was to assess the feasibility of PBCC, including patterns of oxygen saturation (SpO₂) and heart rate (HR) during stabilisation in preterm infants using a new purpose-built resuscitation table.

DESIGN

Observational study.

SETTING

Tertiary referral centre, Leiden University Medical Centre, The Netherlands.

PATIENTS

Infants born below 35 weeks' gestational age.

INTERVENTIONS

Infants were stabilised on a new purpose-built resuscitation table (Concord), provided with standard equipment needed for stabilisation. Cord clamping was performed when the infant was stable (HR >100 bpm, spontaneous breathing on continuous positive airway pressure with tidal volumes >4 mL/kg, SpO₂ ≥25th percentile and fraction of inspired oxygen (FiO₂) <0.4).

RESULTS

Thirty-seven preterm infants were included; mean (SD) gestational age of 30.9 (2.4) weeks, birth weight 1580 (519) g. PBCC was successful in 33 infants (89.2%) and resulted in median (IQR) cord clamping time of 4:23 (3:00-5:11) min after birth. There were no maternal or neonatal adverse events. In 26/37 infants, measurements were adequate for analysis. HR was 113 (81-143) and 144 (129-155) bpm at 1 min and 5 min after birth. SpO₂ levels were 58%(49%-60%) and 91%(80%-96%)%), while median FiO₂ given was 0.30 (0.30-0.31) and 0.31 (0.25-0.97), respectively.

CONCLUSION

PBCC in preterm infants using the Concord is feasible. HR remained stable, and SpO₂ quickly increased with low levels of oxygen supply.

TRIAL REGISTRATION NUMBER

NTR6095, results.

Effect of lung hypoplasia on the cardiorespiratory transition in newborn lambs

Newborns with lung hypoplasia (LH) commonly have limited respiratory function and often require ventilatory assistance after birth. We aimed to characterize the cardiorespiratory transition and respiratory function in newborn lambs with LH. LH was induced by draining fetal lung liquid in utero [110-133 days (d), term = 147d, n = 6]. At ~133d gestation, LH and Control lambs (n = 6) were instrumented and ventilated for 3 h to monitor blood-gas status, oxygenation, ventilator requirements, and hemodynamics during the transition from fetal to newborn life. Lambs with LH had significantly reduced relative wet and dry lung weights indicating hypoplastic lungs compared with Control lambs. LH lambs experienced persistent hypercapnia and acidosis during the ventilation period, had lower lung compliance, and had higher alveolar-arterial differences in oxygen and oxygenation index compared with Control lambs. As a result, LH lambs required greater respiratory support and more supplemental oxygen. Following delivery, LH lambs experienced periods of significantly lower pulmonary artery blood flow and higher carotid artery blood flow in association with the lower oxygenation levels. The detrimental effects of LH can be attributed to a reduction in lung size and poorer gas exchange capabilities. This study has provided greater understanding of the effect of LH itself on the physiology underpinning the transition from fetal to newborn life. Advances in this area is the key to identifying improved or novel management strategies for babies with LH starting in the delivery room, to favorably alter the fetal-to-newborn transition toward improved outcomes and reduced lifelong morbidity.NEW & NOTEWORTHY Current clinical management of newborns with lung hypoplasia (LH) is largely based on expert opinion rather than scientific evidence. We have generated physiological evidence for detrimental effects of LH on hemodynamics and respiratory function in newborn lambs, which mimics the morbidity observed in LH newborns clinically. The unfavorable consequences of LH can be attributed to a reduction in lung size and poorer gas exchange capabilities.

Effect of early versus delayed cord clamping in neonate on heart rate, breathing and oxygen saturation during first 10 minutes of birth - randomized clinical trial

Background

Delayed cord clamping (DCC) after 180 s reduces iron deficiency up to 8 months of infancy compared to babies who received Early Cord Clamping (ECC) at less than 60 s. Experimentally DCC has shown to improve cardio-vascular stability. To evaluate the effect of delayed (≥180 s) group versus early (≤60 s) cord clamping group on peripheral blood oxygenation and heart rate up to 10 min after birth on term and late preterm infants.

Methods

We conducted a single centred randomized clinical trial in a low risk delivery unit in tertiary Hospital, Nepal. One thousand five hundred ten women, low risk vaginal delivery with foetal heart rate (FHR) ≥ 100 ≤ 160 beats per minute (bpm) and gestational age (≥33 weeks) were enrolled in the study. Participants were randomly assigned to cord clamped ≤60 s of birth and ≥ 180 s. The main outcome measures were oxygen saturation, heart rate from birth to 10 min and time of spontaneous breathing. The oxygen saturation and heart rate, the time of first breath and establishment of regular breathing was analysed using Student t-test to compare groups. We analysed the range of heart rate distributed by different centiles from the time of birth at 30 s intervals until 10 min.

Results

The oxygen saturation was 18% higher at 1 min, 13% higher at 5 min and 10% higher at 10 min in babies who had cord clamping in delayed group compared to early group (p < 0.001). The heart rate was 9 beats lower at 1 min and3 beats lower at 5 min in delayed group compared to early group (p < 0.001). Time of first breath and regular breathing was established earlier in babies who had cord clamping at 180 s or more.

Conclusion

Spontaneously breathing babies subjected to DCC have higher oxygen saturation up to 10 min after birth compared to those who have undergone ECC. Spontaneously breathing babies with DCC have lower heart rates compared to ECC until 390 s. Spontaneously breathing babies receiving DCC have early establishment of breathing compared to ECC.

Trial registration

ISRCTN, 5 April 2016.

Transitional fetal hemodynamics and gas exchange in premature postpartum adaptation: immediate vs. delayed cord clamping

Background

Recent studies suggest that delayed cord clamping (DCC) is advantageous for achieving hemodynamic stability and improving oxygenation compared to the immediate cord clamping (ICC) during fetal-to-neonatal transition yet there is no quantitative information on hemodynamics and respiration, particularly for pre-term babies and fetal disease states. Therefore, the objective of this study is to investigate the effects of ICC and DCC on hemodynamics and respiration of the newborn preterm infants in the presence of common vascular pathologies.

Methods

A computational lumped parameter model (LPM) of the placental and respiratory system of a fetus is developed to predict blood pressure, flow rates and oxygen saturation. Cardiovascular system at different gestational ages (GA) are modeled using scaling relations governing fetal growth with the LPM. Intrauterine growth restriction (GR), patent ductus arteriosus (PDA) and respiratory distress syndrome (RDS) were modeled for a newborn at 30 weeks GA. We also formulated a "severity index (SI)" which is a weighted measure of ICC vs. DCC based on the functional parameters derived from our model and existing neonatal disease scoring systems.

Results

Our results show that transitional hemodynamics is smoother in DCC compared to ICC for all GAs. Blood volume of the neonate increases by 10% for moderately preterm and term infants (32-40 wks) and by 15% for very and extremely preterm infants (22-30 wks) with DCC compared to ICC. DCC also improves the cardiac output and the arterial blood pressure by 17% in term (36-40 wks), by 18% in moderately preterm (32-36 wks), by 21% in very preterm (28-32 wks) and by 24% in extremely preterm (20-28 wks) births compared to the ICC. A decline in oxygen saturation is observed in ICC received infants by 20% compared to the DCC received ones. At 30 weeks GA, SI were calculated for healthy newborns (1.18), and newborns with GR (1.38), PDA (1.22) and RDS (1.2) templates.

Conclusion

Our results suggest that DCC provides superior hemodynamics and respiration at birth compared to ICC. This information will help preventing the complications associated with poor oxygenation arising in premature births and pre-screening the more critical babies in terms of their cardiovascular severity.

Antenatal betamethasone augments early rise in pulmonary perfusion at birth in preterm lambs: role of ductal shunting and right ventricular outflow distribution

The glucocorticosteroid betamethasone is routinely administered via maternal intramuscular injection to enhance fetal lung maturation before anticipated preterm birth. Although antenatal betamethasone increases fetal pulmonary arterial (PA) blood flow, whether this agent alters the contribution of 1) right ventricular (RV) output or 2) left-to-right shunting across the ductus arteriosus to rises in PA blood flow after preterm birth is unknown. To address this question, anesthetized control (n = 7) and betamethasone-treated (n = 7) preterm fetal lambs (gestation 127 ± 1 days, means ± SD) were instrumented with aortic, pulmonary, and left atrial catheters as well as ductus arteriosus and left PA flow probes to calculate RV output, with hemodynamics measured for 30 min after cord clamping and mechanical ventilation. Mean PA blood flow was higher in betamethasone-treated than in control lambs over the initial 10 min after birth (P < 0.05). This higher PA flow was accompanied by 1) a greater pulmonary vascular conductance (P ≤ 0.025), 2) a larger proportion of RV output passing to lungs (P ≤ 0.01), despite a fall in this output, and 3) earlier reversal and a greater magnitude (P ≤ 0.025) of net ductal shunting, due to the combination of higher left-to-right (P ≤ 0.025) and lesser right-to-left phasic shunting (P ≤ 0.025). These results suggest that antenatal betamethasone augments the initial rise in PA blood flow after birth in preterm lambs, with this augmented rise supported by the combination of 1) a greater redistribution of RV output toward the lungs and 2) a faster and larger reversal in net ductal shunting underpinned not only by greater left-to-right, but also by lesser right-to-left phasic shunting.

Haemodynamic Instability and Brain Injury in Neonates Exposed to Hypoxia⁻Ischaemia

Brain injury in the asphyxic newborn infant may be exacerbated by delayed restoration of cardiac output and oxygen delivery. With increasing severity of asphyxia, cerebral autoregulatory responses are compromised. Further brain injury may occur in association with high arterial pressures and cerebral blood flows following the restoration of cardiac output. Initial resuscitation aims to rapidly restore cardiac output and oxygenation whilst mitigating the impact of impaired cerebral autoregulation. Recent animal studies have indicated that the current standard practice of immediate umbilical cord clamping prior to resuscitation may exacerbate injury. Resuscitation prior to umbilical cord clamping confers several haemodynamic advantages. In particular, it retains the low-resistance placental circuit that mitigates the rebound hypertension and cerebrovascular injury. Prolonged cerebral hypoxia⁻ischaemia is likely to contribute to further perinatal brain injury, while, at the same time, tissue hyperoxia is associated with oxidative stress. Efforts to monitor and target cerebral flow and oxygen kinetics, for example, using near-infrared spectroscopy, are currently being evaluated and may facilitate development of novel resuscitation approaches.

Reducing lung liquid volume increases biventricular outputs and systemic arterial blood flows despite decreased cardiac filling pressures in fetal lambs

As prior work has shown that reducing lung liquid volume 1) increases pulmonary arterial (PA) blood flow, 2) augments right ventricular (RV) output/power, and 3) decreases left atrial (LA) pressure, we tested the hypothesis that this perturbation has global cardiovascular effects. Ten anesthetized, open-chest fetal lambs (128 ± 2 days gestation, full term = 147 days) were acutely instrumented with 1) LA and right atrial (RA) catheters, 2) aortic and pulmonary trunk catheters, 3) brachiocephalic trunk, aortic isthmus, ductal, and left PA flow probes to obtain left ventricular (LV) and RV outputs and hydraulic power and flow in the descending thoracic aorta, and 4) an endotracheal tube to remove lung liquid. A 17 ± 7 ml/kg reduction of lung liquid volume 1) decreased LA and RA pressures similarly (1.5-1.6 mmHg, P < 0.001), 2) augmented LV and RV outputs (21-24%, P < 0.001) and total power (27-28%, P < 0.005), 3) increased systolic flows in the brachiocephalic trunk (18%, P < 0.001), aortic isthmus (29%, P < 0.005), ductus (12%, P < 0.005), and descending thoracic aorta (16%, P < 0.001), 4) increased mean PA flow via a higher systolic inflow (37%, P < 0.001) and lower diastolic backflow (-16%, P < 0.05), and 5) did not change systemic vascular conductance or arterial compliance but increased both pulmonary vascular conductance and arterial compliance (1.8-fold, P < 0.001). These data suggest that hemodynamic effects of lung liquid volume reduction are not confined to the lungs but extend to all cardiac chambers via rises in LV and RV outputs and power, despite falls in cardiac filling pressures, as well as the systemic circulation, via downstream increases in systolic flows of major central arteries.