Issues in cardiopulmonary transition at birth

Preterm Infants Who Did Not Need Positive Pressure Ventilation Had a Lower Heart Rate Immediately After Birth Than Healthy Term Infants

AIM

Our aim was to use electrocardiograms immediately after birth to determine the heart rates of healthy newborn infants by gestational age and mode of delivery.

METHODS

This prospective observational study was performed in two Norwegian hospitals from March 2019 to June 2021. We included infants with gestational ages of ≥ 28 weeks and no need for positive pressure ventilation. Continuous heart rate data were collected using dry electrode technology and were used to create percentile charts and compare heart rates by groups.

RESULTS

We enrolled 214 preterm and 2191 term newborn infants. The median (quartiles) heart rate at 60 s of age was 166 (150-181) beats per minute for preterm infants and 174 (158-187) for term infants (p < 0.05). Term infants born using vacuum extraction, forceps or emergency Caesarean sections had significantly higher heart rates than term infants born by unassisted vaginal deliveries or planned Caesarean sections. The median heart rates of the groups were all within the normal range.

CONCLUSION

This study provided normative heart rate data for healthy newborn infants, by gestational age and delivery mode. Although the differences between the groups were statistically significant, they were of limited clinical significance and would not support changes in neonatal resuscitation measures.

The effect of histological and subclinical chorioamnionitis and funisitis on breathing effort in premature infants at birth: a retrospective cohort study

Antenatal inflammation in the form of chorioamnionitis (fetal membranes; HCA) and funisitis (umbilical vessels; FUN) is a major risk factor for preterm birth. Exposure to HCA + FUN affects infants by releasing mediators that may suppress respiratory drive. While the association between clinical chorioamnionitis (CCA) and (depressed) spontaneous breathing has been described, we have investigated the association between breathing and HCA + FUN. Infants born < 30 weeks' gestation with available placental pathology assessments were included. Infants were compared at multiple levels: infants with vs without HCA + FUN (comparison 1) and infants with subclinical HCA + FUN vs infants without any chorioamnionitis (comparison 2). The primary outcome was breathing effort, defined as minute volume (MV) of spontaneous breathing in the first 5 min after birth. We also assessed tidal volume (Vt), respiratory rate (RR), heart rate (HR), oxygen saturation (SpO2) and oxygen requirement (FiO2). Regression analyses were performed to control for confounding factors. One hundred eighty-six infants were included (n = 75 infants with HCA + FUN vs. n = 111 infants without HCA + FUN). Comparison 1: Infants with HCA + FUN had lower gestational ages 26+5 (25+0-28+1; median (IQR) and lower birthweights (mean ± SD; 943 ± 264) compared to infants without HCA + FUN (28+4 (27+0-29+1) weeks, p < 0.001 and 1023 ± 270 g, p = 0.049). Comparison 2: Subclinical HCA + FUN was diagnosed in 46/75 HCA + FUN infants. Infants with subclinical HCA + FUN had lower gestational ages (26+6 (25+1-28+3) vs. 28+4 (27+2-29+1) weeks, p < 0.001) without significant differences for birthweights (987 ± 248 vs. 1027 ± 267 g, p = 0.389) compared to infants without any chorioamnionitis (n = 102 infants). After adjustment, HCA + FUN was associated with lower MV (p = 0.025), but subclinical HCA + FUN was not (p = 0.226). HCA + FUN and subclinical HCA + FUN were associated with lower Vt (p = 0.003; p = 0.014), SpO2 at 5 min (p = 0.021; 0.036) and SpO2/FiO2 ratio (p = 0.028; p = 0.040).

CONCLUSION

HCA + FUN and subclinical HCA + FUN are associated with reduced oxygenation and parameters that reflect breathing effort in premature infants at birth.

WHAT IS KNOWN

• Acute antenatal inflammation, in the form of chorioamnionitis (fetal membranes) and funisitis (umbilical vessels), affects a large proportion of premature infants. • Clinical chorioamnionitis is associated with reduced breathing effort and oxygenation in premature infants at birth.

WHAT IS NEW

• Histological and subclinical chorioamnionitis and funisitis are associated with reduced breathing effort parameters and oxygenation in premature infants at birth.

Effect of Delayed Cord Clamping on Breastfeeding Behaviors During the First Breastfeed: A Randomized Controlled Study

Objective: Delayed cord clamping (DCC) may increase the success of breastfeeding by improving neurological and cardiovascular function in neonates. In this study, we investigated the impact of DCC on breastfeeding behaviors, neonatal activity status, and maternal satisfaction during the first breastfeeding. Methods: This randomized controlled study was conducted in a tertiary hospital in Turkey with 100 term infants delivered by elective cesarean section with spinal anesthesia. The participants were randomly assigned to the early cord clamping (ECC) group or DCC group. The Infant Breastfeeding Assessment Tool (IBFAT) was used to assess infant alertness, breastfeeding behaviors, and maternal satisfaction with breastfeeding within the first 2 hours of life. Results: Scores on the IBFAT were significantly higher in the DCC group compared with the ECC group (p = 0.02). Maternal satisfaction with breastfeeding did not differ between the groups (p = 0.3). Infant alertness tended to be better in the DCC group, but the difference was not statistically significant (p = 0.08). Conclusion: The results of this study indicated that DCC was associated with more favorable breastfeeding behaviors compared with ECC.

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.

Transferring an extremely premature infant to an extra-uterine life support system: a prospective view on the obstetric procedure

To improve care for extremely premature infants, the development of an extrauterine environment for newborn development is being researched, known as Artificial Placenta and Artificial Womb (APAW) technology. APAW facilitates extended development in a liquid-filled incubator with oxygen and nutrient supply through an oxygenator connected to the umbilical vessels. This setup is intended to provide the optimal environment for further development, allowing further lung maturation by delaying gas exposure to oxygen. This innovative treatment necessitates interventions in obstetric procedures to transfer an infant from the native to an artificial womb, while preventing fetal-to-neonatal transition. In this narrative review we analyze relevant fetal physiology literature, provide an overview of insights from APAW studies, and identify considerations for the obstetric procedure from the native uterus to an APAW system. Lastly, this review provides suggestions to improve sterility, fetal and maternal well-being, and the prevention of neonatal transition.

Observational study comparing heart rate in crying and non-crying but breathing infants at birth

BACKGROUND

Stimulating infants to elicit a cry at birth is common but could result in unnecessary handling. We evaluated heart rate in infants who were crying versus non-crying but breathing immediately after birth.

METHODS

This was single-centre observational study of singleton, vaginally born infants at ≥33 weeks of gestation. Infants who were crying or non-crying but breathing within 30 s after birth were included. Background demographic data and delivery room events were recorded using tablet-based applications and synchronised with continuous heart rate data recorded by a dry-electrode electrocardiographic monitor. Heart rate centile curves for the first 3 min of life were generated with piecewise regression analysis. Odds of bradycardia and tachycardia were compared using multiple logistic regression.

RESULTS

1155 crying and 54 non-crying but breathing neonates were included in the final analyses. There were no significant differences in the demographic and obstetric factors between the cohorts. Non-crying but breathing infants had higher rates of early cord clamping <60 s after birth (75.9% vs 46.5%) and admission to the neonatal intensive care unit (13.0% vs 4.3%). There were no significant differences in median heart rates between the cohorts. Non-crying but breathing infants had higher odds of bradycardia (heart rate <100 beats/min, adjusted OR 2.64, 95% CI 1.34 to 5.17) and tachycardia (heart rate ≥200 beats/min, adjusted OR 2.86, 95% CI 1.50 to 5.47).

CONCLUSION

Infants who are quietly breathing but do not cry after birth have an increased risk of both bradycardia and tachycardia, and admission to the neonatal intensive care unit.

TRIAL REGISTRATION NUMBER

ISRCTN18148368.

Increased risk of bradycardia in vigorous infants receiving early as compared to delayed cord clamping at birth

OBJECTIVE

To compare HR pattern of vigorous newborns during the first 180 s with early (≤60 s, ECC) or delayed (>60 s, DCC) cord clamping.

STUDY DESIGN

Observational study including dry-electrode ECG monitoring of 610 vaginally-born singleton term and late-preterm (≥34 weeks) who were vigorous after birth.

RESULTS

198 received ECC while 412 received DCC with median cord clamping at 37 s and 94 s. Median HR remained stable from 30 to 180 s with DCC (172 and 170 bpm respectively) but increased with ECC (169 and 184 bpm). The proportion with bradycardia was higher among ECC than DCC at 30 s and fell faster in the DCC through 60 s. After adjusting for factors affecting timing of cord clamping, ECC had significant risk of bradycardia compared to DCC (aRR 1.51; 95% CI; 1.01-2.26).

CONCLUSION

Early heart instability and higher risk of bradycardia with ECC as compared to DCC supports the recommended clinical practice of DCC.

Effect of clinical chorioamnionitis on breathing effort in premature infants at birth: a retrospective case-control study

RATIONALE

Antenatal inflammation, usually associated with chorioamnionitis, is a major cause of premature birth. As inflammation could depress respiratory drive, we have examined the effect of clinical chorioamnionitis (CCA) on spontaneous breathing in premature infants at birth.

METHODS

Infants with CCA born <30 weeks' gestation were matched with control infants based on gestational age (±6 days), birth weight (±300 g), antenatal corticosteroids, sex and general anaesthesia. The primary outcome was breathing effort, assessed as minute volume (MV) of spontaneous breathing. We also measured tidal volume (Vt), respiratory rate (RR) and apnoea in the first 5 min and additional physiological parameters in the first 10 min after start of respiratory support.

RESULTS

Ninety-two infants were included (n=46 CCA infants vs n=46 controls; median (IQR) gestational age 26⁺⁴ (25⁺⁰-27⁺⁶) vs 26⁺⁶ (25⁺¹-28⁺³) weeks). MV and Vt were significantly lower (MV: 43 (17-93) vs 70 (31-119) mL/kg/min, p=0.043; Vt: 2.6 (1.9-3.6) vs 2.9 (2.2-4.8) mL/kg/breath, p=0.046), whereas RR was similar in CCA infants compared with controls. Incidence of apnoea was higher (5 (2-6) vs 2 (1-4), p=0.002), and total duration of apnoea was longer (90 (21-139) vs 35 (12-98) s, p=0.025) in CCA infants. CCA infants took significantly longer to reach an oxygen saturation >80% (3:37 (2:10-4:29) vs 2:25 (1:06-3:52) min, p=0.016) and had a lower oxygen saturation at 5 min (77 (66-92) vs 91 (68-94) %, p=0.028), despite receiving more oxygen (62 (48-76) vs 54 (43-73) %, p=0.036).

CONCLUSION

CCA is associated with reduced breathing effort and oxygenation in premature infants at birth.

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.

Resuscitation 2020: Proceedings From the NeoHeart 2020 International Conference

Resuscitation guidelines are developed and revised by medical societies throughout the world. These guidelines are increasingly based on evidence from preclinical and clinical research. The International Liaison Committee on Resuscitation reviews evidence for each resuscitation practice and provides summary consensus statements that inform resuscitation guideline committees. A similar process is used for different populations including neonatal, pediatric, and adult resuscitation. The NeoHeart 2020 Conference brought together experts in resuscitation to discuss recent evidence and guidelines for resuscitation practices. This review summarizes the main focus of discussion from this symposium.

Dynamics of cortical oxygenation during immediate adaptation to extrauterine life

The neonatal transition involves physiological modifications as a consequence of the complexity of the perinatal period. Various strategies can be used to attain the same level of postnatal cerebral oxygenation, depending on the status of the infant at birth. We evaluated such strategies by recording 20 full-term newborns by near-infrared spectroscopy during the first 10 min of life. The acid–base status at birth revealed two clustered profiles of cerebral oxygenation dynamics. Lower pH and base excess and higher lactate levels were associated with more rapid attainment of the 95% maximal tissue oxygenation index value. These results suggest that metabolic mechanisms drive initial cerebral oxygenation dynamics during this critical period. These results confirm the capacity of newborns to develop multiple strategies to protect the brain.

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.

Changes in heart rate from 5 s to 5 min after birth in vaginally delivered term newborns with delayed cord clamping

OBJECTIVE

To determine heart rate centiles during the first 5 min after birth in healthy term newborns delivered vaginally with delayed cord clamping.

DESIGN

Single-centre prospective observational study.

SETTING

Stavanger University Hospital, Norway, March-August 2019.

PATIENTS

Term newborns delivered vaginally were eligible for inclusion. Newborns delivered by vacuum or forceps or who received any medical intervention were excluded.

INTERVENTIONS

A novel dry electrode electrocardiography monitor (NeoBeat) was applied to the newborn's chest immediately after birth. The newborns were placed on their mother's chest or abdomen, dried and stimulated, and cord clamping was delayed for at least 1 min.

MAIN OUTCOME MEASURES

Heart rate was recorded at 1 s intervals, and the 3rd, 10th, 25th, 50th, 75th, 90th and 97th centiles were calculated from 5 s to 5 min after birth.

RESULTS

898 newborns with a mean (SD) birth weight 3594 (478) g and gestational age 40 (1) weeks were included. The heart rate increased rapidly from median (IQR) 122 (98-146) to 168 (146-185) beats per minute (bpm) during the first 30 s after birth, peaking at 175 (157-189) bpm at 61 s after birth, and thereafter slowly decreasing. The third centile reached 100 bpm at 34 s, suggesting that heart rates <100 bpm during the first minutes after birth are uncommon in healthy newborns after delayed cord clamping.

CONCLUSION

This report presents normal heart rate centiles from 5 s to 5 min after birth in healthy term newborns delivered vaginally with delayed cord clamping.