Incompetence of the foramen ovale in preterm infants supported by mechanical ventilation

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.

Transitional circulation and hemodynamic monitoring in newborn infants

Transitional circulation is normally transient after birth but can vary markedly between infants. It is actually in a state of transition between fetal (in utero) and neonatal (postnatal) circulation. In the absence of definitive clinical trials, information from applied physiological studies can be used to facilitate clinical decision making in the presence of hemodynamic compromise. This review summarizes the peculiar physiological features of the circulation as it transitions from one phenotype into another in term and preterm infants. The common causes of hemodynamic compromise during transition, intact umbilical cord resuscitation, and advanced hemodynamic monitoring are discussed. IMPACT: Transitional circulation can vary markedly between infants. There are alterations in preload, contractility, and afterload during the transition of circulation after birth in term and preterm infants. Hemodynamic monitoring tools and technology during neonatal transition and utilization of bedside echocardiography during the neonatal transition are increasingly recognized. Understanding the cardiovascular physiology of transition can help clinicians in making better decisions while managing infants with hemodynamic compromise. The objective assessment of cardio-respiratory transition and understanding of physiology in normal and disease states have the potential of improving short- and long-term health outcomes.

Pulmonary hemorrhage in extremely low birth weight infants: Significance of the size of left to right shunting through a valve incompetent patent foramen ovale

OBJECTIVE

Pulmonary hemorrhage is a rare but severe complication of extremely low birth weight (ELBW) infants. The association of hemodynamically significant patent ductus arteriosus (hsPDA) and the diameter of the foramen ovale (FO) with pulmonary hemorrhage has not been reported.

STUDY DESIGN

Case control study of ELBW infants with and without pulmonary hemorrhage. Each ELBW infant with an echocardiogram within 48 h of pulmonary hemorrhage was analyzed.

RESULT

16 infants with pulmonary hemorrhage were matched with 32 controls by birth weight and gestational age. Echocardiogram showed hsPDA in all infants and those with pulmonary hemorrhage had significantly smaller patent FO [PFO] (1 vs 2.4 mm, p < 0.01) (OR 0.007; 95% CI 0.00007, 0.67 p = 0.03). Incidence of pulmonary hemorrhage was 8.9%.

CONCLUSION

ELBW infants with hsPDA who experienced pulmonary hemorrhage had a significantly restricted or closed FO. Evaluation of FO should be considered with serial echocardiograms when evaluating for hsPDA.

Multimodal Assessment of Systemic Blood Flow in Infants

The assessment of systemic blood flow is a complex and comprehensive process with clinical, laboratory, and technological components. Despite recent advancements in technology, there is no perfect bedside tool to quantify systemic blood flow in infants that can be used for clinical decision making. Each option has its own merits and limitations, and evidence on the reliability of these physiology-based assessment processes is evolving. This article provides an extensive review of the interpretation and limitations of methods to assess systemic blood flow in infants, highlighting the importance of a comprehensive and multimodal approach in this population.

Impact of Aortic Diameter Measurements at Three Anatomical Landmarks on Left Ventricular Output Calculation in Neonates

OBJECTIVES

To assess reproducibility and accuracy of left ventricular output (LVO) quantifications in neonates, when left ventricular outflow tract diameter (LVOTD) was measured at the hinges of the aortic valve (AV), at the aortic sinus (AS), and at the sinotubular junction (STJ).

METHODS

This was an observational study. In the first cohort of very preterm neonates, we assessed intraobserver and interobserver repeatability of LVOTD measured at the AV, AS, and STJ and of the corresponding LVO. In the second cohort of older neonates, we compared paired LVO measurements by echo and magnetic resonance imaging (MRI).

RESULTS

In the first cohort of 48 neonates, mean (standard deviation) weight and age at scan were 1046 (302) g and 28.1 (2.7) weeks. Interobserver bias (95% limits of agreement [LOA]) for LVOTD at the AV, AS, and STJ was 0 (-0.3 to 0.3) mm, 0 (-0.7 to 0.7) mm, and 0 (-0.8 to 0.7) mm, respectively. Interobserver bias (95% LOA) for the corresponding LVO was -1.3 (-31 to 33) ml/kg/min, -0.5 (-88 to 87) ml/kg/min, and -7.2 (-83 to 69) ml/kg/min, respectively. In the second cohort of 10 neonates, median (range) weight and age at scan were 1942 (970-3640) g and 37.2 (31.7-39.8) weeks. LVO measured at the AV showed stronger agreement with MRI: bias (LOA) -10.6 (-74 to 52) ml/kg/min, compared to LVO measured at AS and STJ: 194 (-0.5 to 388) ml/kg/min and 43 (-72 to 159) ml/kg/min respectively.

CONCLUSIONS

Reproducibility and accuracy of LVO quantification by echo were better when aortic diameter was measured at AV.

Early Role of the Atrial-Level Communication in Premature Infants with Patent Ductus Arteriosus

BACKGROUND

High-volume systemic-to-pulmonary ductus arteriosus shunts in premature infants are associated with adverse neonatal outcomes. The role of an atrial communication (AC) in modulating the effects of a presumed hemodynamically significant patent ductus arteriosus (PDA) is poorly studied. The objective of this study was to characterize the relationship between early AC and echocardiographic indices of PDA shunt volume and clinical neonatal outcomes.

METHODS

A retrospective review of preterm infants (born at <32 weeks' gestation) who underwent echocardiography in the first postnatal week was performed. The cohort was divided into four groups on the basis of presence of a presumed hemodynamically significant PDA (≥1.5 vs <1.5 mm) and AC size (≤1 vs >1 mm), and echocardiographic measures of PDA shunt volume were then compared. Clinical outcomes, including chronic lung disease and intraventricular hemorrhage, were also compared among all four groups.

RESULTS

A total of 199 preterm infants (mean birth weight, 928 ± 632 g; mean gestational age, 26.6 ± 1.5 weeks) were identified; 159 infants had PDAs ≥ 1.5 mm, of whom 52 had ACs ≤ 1 mm and 107 had ACs > 1 mm. The remaining 40 infants had PDAs < 1.5 mm, of whom 23 had ACs ≤ 1 mm and 17 had ACs > 1 mm. Infants with PDAs ≥ 1.5 mm and ACs > 1 mm had higher pulmonary vein D-wave velocities (P < .05), higher left ventricular output (P < .005), higher PDA scores (P < .001), and increased rates of reversed diastolic flow in the descending aorta (P < .001), celiac artery (P < .001), and middle cerebral artery (P < .001) than infants with either PDAs < 1.5 mm or PDAs ≥ 1.5 mm and ACs ≤ 1 mm. There was no difference in the incidence of intraventricular hemorrhage, but infants with PDAs ≥ 1.5 mm and ACs > 1 mm had a higher risk for a composite outcome of chronic lung disease or death before hospital discharge (P < .05).

CONCLUSIONS

Echocardiographic evidence of ACs > 1 mm in patients with PDAs ≥ 1.5 mm during the first postnatal week may be a marker of a more pathologic hemodynamically significant PDA in premature infants. Future investigations should evaluate if early identification and treatment of patients with both high-volume PDAs and larger atrial-level communications may help mitigate adverse outcomes, such as chronic lung disease or death, in this high-risk patient population.

Comparison of Two Techniques of Superior Vena Cava Flow Measurement in Preterm Infants With Birth Weight <1,250 g in the Transitional Period-Prospective Observational Cohort Study

Objectives: Superior Vena Cava (SVC) flow in neonates measured by the standard approach has been validated by different groups around the world. The modified SVC flow measurement technique was recently suggested. The aim of our study was to evaluate standard and modified technique of echocardiography SVC flow measurement in a cohort of extremely preterm neonates in the immediate postnatal period. Methods: Prospective, observational cohort study in a level III neonatal center. Infants with birth weight <1,250 g were eligible for enrolment. SVC flow was measured by echocardiography using standard and modified methods at 6, 18 and 36 h of age. Our primary outcome was equivalency (using raw bounds of -20 to +20 mL/kg/min difference between the paired measurements), agreement and correlation between standard and modified methods of the SVC flow measurements. Results: Thirty-nine infants were enrolled. The mean gestational age of the cohort was 27.4 (SD 2.1) weeks of postmenstrual age, the mean birth weight was 0.95 kg (SD 0.2). The measurements at 6 and 36 h of age were equivalent as defined in the design of the study (p = 0.003 and p = 0.004 respectively; raw bounds -20 to +20 mL/kg/min). At 6 h of age the mean difference (bias) between the measurements was -0.8 mL/kg/min with 95% limits of agreement -65.0 to 63.4 mL/kg/min. At 18 h of age, the mean difference (bias) between the measurements was +9.5 mL/kg/min, with 95% limits of agreement -79.6 to 98.7 mL/kg/min. At 36 h of age the mean difference (bias) between the measurements was -2.2 mL/kg/min with 95% limits of agreement -73.4 to 69.1 mL/kg/min. There was a weak, but statistically significant correlation between the standard and modified method at 6 h of age (r = 0.39, p = 0.04). Conclusion: Both SVC flow echocardiography measurement techniques yielded clinically equivalent results, however due to wide limits of agreement and poor correlation they do not seem to be interchangeable.

Repair of isolated atrial septal defect in infants less than 12 months improves symptoms of chronic lung disease or shunt-related pulmonary hypertension

INTRODUCTION

Infants with isolated atrial septal defects are usually minimally symptomatic, and repair is typically performed after infancy. Early repair may be considered if there is high pulmonary blood flow and reduced respiratory reserve or early signs of pulmonary hypertension. Our aim was to review the characteristics and outcomes of a cohort of patients who underwent infant repair at our institute.

METHODS

The study included 56 infants (28 female, 19 trisomy 21) with isolated atrial septal defect (age: 8 months (1.5-12), weight: 6 kg (2.8-7.5), echo Qp/Qs: 1.9 ± 0.1) who underwent surgical closure (20 fenestrated). Three groups were identified: 1) chronic lung disease and pulmonary hypertension (group A: n = 28%); 2) acutely unwell infants with pulmonary hypertension but no chronic lung disease (group B: n = 20, 36%); and 3) infants with refractory congestive heart failure without either pulmonary hypertension or chronic lung disease (group C: n = 9, 16%).

RESULTS

Post-operatively, pulmonary hypertension infants (47/56) showed improvement in tricuspid annular plane systolic excursion z-score (p < 0.001) and right ventricular systolic/diastolic duration ratio (p < 0.05). All ventilator (14.3%) or oxygen-dependent (31.6%) infants could be weaned within 2 weeks after repair. One year later, weight z-score increased in all patients and by +1 in group A, +1.3 in group B and +2 in group C. Over a median follow-up of 1.4 years, three patients died, four patients continued to have pulmonary hypertension evidence and two remained on targeted pulmonary hypertension therapy.

CONCLUSION

Atrial septal defect repair within the first year may improve the clinical status and growth in infants with early signs of pulmonary hypertension or those requiring respiratory support and facilitate respiratory management.

Pulmonary Venous Congestion and Pulmonary Hemorrhage in an Extremely Premature Neonate With a Large Patent Ductus Arteriosus and Closed Patent Foramen Ovale: A Case Report

We describe a case of an extremely low birthweight infant with a large patent ductus arteriosus and closed foramen ovale resulting in markedly increased pulmonary blood flow, pulmonary venous congestion, and pulmonary hemorrhage.

Non-invasive Cardiac Output Monitoring in Neonates

Circulatory monitoring is currently limited to heart rate and blood pressure assessment in the majority of neonatal units globally. Non-invasive cardiac output monitoring (NiCO) in term and preterm neonates is increasing, where it has the potential to enhance our understanding and management of overall circulatory status. In this narrative review, we summarized 33 studies including almost 2,000 term and preterm neonates. The majority of studies evaluated interchangeability with echocardiography. Studies were performed in various clinical settings including the delivery room, patent ductus arteriosus assessment, patient positioning, red blood cell transfusion, and therapeutic hypothermia for hypoxic ischemic encephalopathy. This review presents an overview of NiCO in neonatal care, focusing on technical and practical aspects as well as current available evidence. We discuss potential goals for future research.

Relationship of Patent Ductus Arteriosus Size to Echocardiographic Markers of Shunt Volume

OBJECTIVE

To define the technique of estimating ductal diameter (DD) that best correlates with echocardiographic markers of transductal shunt volume in preterm infants >7 days old with persistent patent ductus arteriosus (PDA).

STUDY DESIGN

We conducted a retrospective study of 104 neonates born at <30 weeks gestation that had targeted neonatal echocardiography evaluation of PDA performed between 7 and 30 days. We used univariate analysis to determine the association of echocardiographic markers of shunt volume with ductal size definitions: DD, DD indexed to weight, and DD indexed to left pulmonary artery diameter.

RESULTS

Two hundred echocardiograms were reviewed from 104 patients with a median gestational age of 25.4 weeks (range, 25-26.3 weeks) and a median birth weight of 810 g (range, 740-920 g). We found a weak correlation of each method of PDA size definition with individual echocardiographic markers of transductal shunt volume, of which nonindexed DD demonstrated the best correlation. The best correlation was found with markers of systemic hypoperfusion, such as diastolic flow reversal in the descending aorta (R² = 0.24) and celiac artery (R² = 0.21). Markers of pulmonary overcirculation, such as left ventricular end-diastolic diameter (R² = 0.19) and left ventricular output (R² = 0.17), showed fair correlation with nonindexed DD.

CONCLUSION

In preterm infants >7 days old with PDA, nonindexed DD demonstrated weak correlations with individual echocardiographic markers of shunt volume. These data highlight the need for comprehensive echocardiographic evaluation in addition to diameter measurements to provide a better understanding of the hemodynamic consequences of PDA.

The role of Neonatologist Performed Echocardiography in the assessment and management of neonatal shock

One of the major challenges of neonatal intensive care is the early detection and management of circulatory failure. Routine clinical assessment of the hemodynamic status of newborn infants is subjective and inaccurate, emphasizing the need for objective monitoring tools. An overview will be provided about the use of neonatologist-performed echocardiography (NPE) to assess cardiovascular compromise and guide hemodynamic management. Different techniques of central blood flow measurement, such as left and right ventricular output, superior vena cava flow, and descending aortic flow are reviewed focusing on methodology, validation, and available reference values. Recommendations are provided for individualized hemodynamic management guided by NPE.

A review of superior vena cava flow measurement in the neonate by functional echocardiography

Neonatologists have begun using superior vena cava flow as assessed by functional echocardiography to facilitate real-time decision-making on cardiovascular care. This review aims to describe the basis of the technique, summarise the evidence for its use and compare the technique to existing clinical, biochemical and radiological techniques for assessing neonatal circulatory status.

CONCLUSION

Although echocardiographic measurements of superior vena cava flow, like other measures of perfusion, are not perfect, their noninvasive nature and ability to facilitate real-time decision-making means that at present, they remain the best available methodology of monitoring central perfusion in the neonatal population.

A physiological approach to the timing of umbilical cord clamping at birth

Umbilical cord clamping at birth has a major impact on an infant's cardiovascular system that varies in significance depending upon whether the infant has commenced breathing. As umbilical venous return is a major source of preload for the left ventricle during fetal life, recent experimental evidence has shown that clamping the umbilical cord severely limits cardiac venous return in the absence of pulmonary ventilation. As a result, cardiac output greatly reduces and remains low until breathing commences. Once the infant begins breathing, aeration of the lung triggers a large increase in pulmonary blood flow, which replaces umbilical venous return as the source of preload for the left ventricle. As a result, cardiac output markedly increases, as indicated by an increase in heart rate immediately after birth. Thus, infants born apnoeic and hypoxic and have their cords immediately clamped, are likely to have a restricted cardiac output combined with hypoxia. As increased cardiac output is a major physiological defence mechanism that counteracts the effects of hypoxaemia, limiting the increase in cardiac output exposes the infant to ischaemia along with hypoxia. However, if the infant commences breathing, aerates its lungs and increases pulmonary blood flow before the umbilical cord is clamped, then pulmonary venous return can immediately take over the supply of left ventricular preload upon cord clamping. As a result, there is no intervening period of reduced preload and cardiac output and the large swings in arterial pressures and flows are reduced leading to a more stable circulatory transition.

Diastolic ventricular function improves during the first 48-hours-of-life in infants weighting <1250 g

AIM

Few studies have focused on cardiac ventricular diastolic function in preterm neonates in the immediate post-natal period. This study evaluated Doppler-derived parameters of diastolic ventricular function in infants with birth weights of <1250 g during the transitional period.

METHODS

This was a prospective observational study conducted in the Coombe Women and Infants University Hospital in Dublin, Ireland. Flow patterns on the mitral and tricuspid valve, isovolumic relaxation time (IVRT), left and right ventricular output and superior vena cava flow were measured in 22 infants with a birth weight of below 1250 g at six, 12, 24 and 48 h of age.

RESULTS

Early filling peak velocity of the left and right ventricle increased significantly from 30.3 to 39.5 cm/sec and 26.6 to 32.1 cm/sec, respectively. IVRT of the right ventricle decreased from 70 to 57 ms, and there was a nonsignificant decrease in IVRT of the left ventricle from 61.6 to 54 ms over the first 48 h.

CONCLUSION

We have demonstrated that parameters of diastolic ventricular function change significantly over the first 48 h of life in preterm infants <1250 g and that these changes may represent early diastolic dysfunction during the transitional period.

Speckle tracking echocardiography in very preterm infants: feasibility and reference values

BACKGROUND

Speckle tracking echocardiography (STE) applies computer software analysis on images generated by conventional ultrasound to define and follow a cluster of speckles from frame to frame and calculates parameters of motion (velocity, displacement) and deformation (strain, strain rate). We explored STE of the left ventricle in stable very preterm infants.

METHODS

Apical 4 chamber clips (4CH) and short axis clips (SAX) at the level of the papillary muscle were analyzed using TomTec software with manual tracing of cardiac borders. The software automatically segmented the ventricle into 6 equidistant segments and provided segmental and global analysis of deformation parameters. Tracking accuracy was scored visually.

RESULTS

Seventy-four clips from 51 infants with a median gestational age of 28weeks were analyzed. Feasibility of 4CH was 95.5% for longitudinal and 96.2% for radial parameters. The reliability of longitudinal and circumferential deformation parameters was good, but radial parameters were less reliable. 4CH mean (SD) global peak systolic longitudinal and radial strain (%) and strain rate (s(-1)) were -18.7(2.6), -1.73(0.28), 23.6(9.1) and 1.94(0.65), and SAX circumferential and radial strain and strain rate were -19.5(3.7), -1.97(0.46), 32.1(14.4) and 2.37(0.80).

CONCLUSION

STE is feasible in preterm infants. Optimal image acquisition is paramount. Longitudinal parameters in 4CH and circumferential in SAX were most robust.

Neonatal hypotension: dopamine or dobutamine?

Controversy surrounds the assessment of perfusion and the methods currently utilised to define hypotension, especially blood pressure. There is growing agreement to assess heart function when selecting inotropic therapy and use bedside tools such as echocardiography for assessing at-risk infants. Both dopamine and dobutamine have comparative efficacy, and in certain disease states with immature myocardium there could be potential advantages in using dobutamine. The concomitant use of hydrocortisone has been shown to be beneficial when escalating doses of first-line inotropes are used. Other inotropes require further study through randomised trials for their safety and efficacy to be established.

Validation study of the accuracy of echocardiographic measurements of systemic blood flow volume in newborn infants

BACKGROUND

The echocardiographic assessment of circulatory function in sick newborn infants has the potential to improve patient care. However, measurements are prone to error and have not been sufficiently validated. Phase-contrast magnetic resonance imaging (MRI) provides highly validated measures of blood flow and has recently been applied to the newborn population. The aim of this study was to validate measures of left ventricular output and superior vena caval flow volume in newborn infants.

METHODS

Echocardiographic and MRI assessments were performed within 1 working day of each other in a cohort of newborn infants.

RESULTS

Examinations were performed in 49 infants with a median corrected gestational age at scan of 34.43 weeks (range, 27.43-40 weeks) and a median weight at scan of 1,880 g (range, 660-3,760 g). Echocardiographic assessment of left ventricular output showed a strong correlation with MRI assessment (R(2) = 0.83; mean bias, -9.6 mL/kg/min; limits of agreement, -79.6 to +60.0 mL/kg/min; repeatability index, 28.2%). Echocardiographic assessment of superior vena caval flow showed a poor correlation with MRI assessment (R(2) = 0.22; mean bias, -13.7 mL/kg/min; limits of agreement, -89.1 to +61.7 mL/kg/min; repeatability index, 68.0%). Calculating superior vena caval flow volume from an axial area measurement and applying a 50% reduction to stroke distance to compensate for overestimation gave a slightly improved correlation with MRI (R(2) = 0.29; mean bias, 2.6 mL/kg/min; limits of agreement, -53.4 to +58.6 mL/kg/min; repeatability index, 54.5%).

CONCLUSIONS

Echocardiographic assessment of left ventricular output appears relatively robust in newborn infant. Echocardiographic assessment of superior vena caval flow is of limited accuracy in this population, casting doubt on the utility of the measurement for diagnostic decision making.

Patent ductus arteriosus in preterm infants is associated with cardiac autonomic alteration and predominant parasympathetic stimulation

BACKGROUND

Hemodynamic disorders in patent ductus arteriosus (PDA) may alter the stimulation of the autonomic nervous system.

AIM

The objective of this study was to analyze the orthosympathetic-parasympathetic balance in preterm infants with PDA.

STUDY DESIGN AND SUBJECTS

Patients were included from consecutive admissions to Amiens University Hospital from 2009 to 2011. We defined a PDA group and a Control group (echographic criteria). For each patient, three 4-minutes segments of ECG were recorded during quiet sleep and the RR chronologic series were extracted, and spectral (Fourier Transform) and time-domain analyses were performed. For each parameter of heart rate variability (HRV), average of three measures was determined and analysed.

RESULTS

Forty-four patients were included for analysis. The total HRV power, LF/HF ratio and SDNN were lower in the PDA group (n = 22, gestational age 28.2 w ± 1.9) than in the Control group (n = 22, gestational age 28.8 w ± 2). The decrease in LF power destabilized the autonomic balance in favour of parasympathetic stimulation. After adjustment for postconceptional age, PDA was still associated with parameters of autonomic neural stimulation.

CONCLUSION

These results suggest association of PDA with predominance of parasympathetic stimulation in preterm infants. The mechanisms of homeostasis in patients with PDA are very complex and involve both circulatory adaptations and control by autonomic pathway. If confirmed, our results could be interesting for future researches aiming to verify the interest of new targeted therapies for the management of PDA.

Altered transitional circulation in infants of diabetic mothers with strict antenatal obstetric management: a functional echocardiography study

OBJECTIVE

Infants born to diabetic mothers (IDMs) even with good glycemic control are at risk for neonatal morbidity. Many of these problems occur during neonatal transition. We assessed (i) systemic and pulmonary blood flow in IDMs compared with controls and (ii) directional blood flow changes within fetal shunts during the first few days of life.

STUDY DESIGN

In this prospective observational cohort study, we evaluated right (RVO) and left ventricular output, superior vena cava flow, atrial and ductal shunts, and tricuspid regurgitation in 32 IDMs and 18 controls using serial echocardiography after birth and 48 h of life in both groups and at 24 and 72 h in IDMs only.

RESULT

IDMs had lower RVO after birth and 48 h of life. IDMs also had less left to right atrial shunt and more right to left ductal shunt after birth compared with controls. In all, 15 of the 32 IDMs were admitted to the neonatal intensive care unit and 11 had respiratory symptoms.

CONCLUSION

Persistence of fetal shunts and decreased RVO in IDMs suggest that even those with good gestational control have impaired transitional hemodynamics.

Inotropes in preterm infants--evidence for and against

There is significant uncertainty regarding the optimal circulatory management of preterm infants, with research in the field limited by the paucity of safe, reproducible biomarkers of circulatory function. This review discusses the physiology and pathophysiology of circulatory function in preterm infants, describes the mode of action and evidence for and against commonly used and recently trialled inotropic therapies and provides recommendations for managing circulatory dysfunction in the transitional period and in the context of sepsis/necrotizing enterocolitis. We recommend a pragmatic approach of assessing multiple aspects of circulatory function (blood pressure alone correlates weakly with volume of flow) in each infant, tailoring therapy on the basis of the change in function desired and frequently reassessing response to intervention.

Disruption of intracardiac flow patterns in the newborn infant

INTRODUCTION

Consistent patterns of rotational intracardiac flow have been demonstrated in the healthy adult human heart. Intracardiac rotational flow patterns are hypothesized to assist in the maintenance of kinetic energy of inflowing blood, augmenting cardiac function. Newborn cardiac function is known to be suboptimal secondary to decreased receptor number and sympathetic innervation, increased afterload, and increased reliance on atrial contraction to support ventricular filling. Patterns of intracardiac flow in the newborn have not previously been examined.

RESULTS

Whereas 5 of the 13 infants studied showed significant evidence of rotational flow within the right atrium, 8 infants showed little or no rotational flow. Presence or absence of rotational flow was not related to gestational age, birth weight, postnatal age, atrial size, or image quality. Despite absence of intra-atrial rotational flow, atrioventricular valve flow into the left and right ventricles later in the cardiac cycle could be seen, suggesting that visualization techniques were adequate.

DISCUSSION

While further study is required to assess its exact consequences on cardiac mechanics and energetics, disruption to intracardiac flow patterns could be another contributor to the multifactorial sequence that produces newborn circulatory failure.

METHODS

We studied 13 newborn infants, using three-dimensional (3D) cardiac magnetic resonance phase-contrast imaging (spatial resolution 0.84 mm, temporal resolution 22.6 ms) performed without sedation/anesthesia.

The scenarios of shock in newborn infants

Shock defines a complex dysfunction of organ perfusion, that produces a status of cellular energy failure, resulting from an insufficient supply of oxygen and nutrients to tissues. The diagnosis of shock is very difficult because of the lack of sufficiently sensitive and specific clinical criteria, and is substantially based on the demonstration of an arterial hypotension, an indicator unfit to detect the organ hypoperfusion. It determines the necessity of firmly introducing in the diagnostic run the functional echocardiography, the near infrared spectroscopy and the amplitude &#x2013; integrated electroencephalography, etc., in the monitoring of the critical newborn. In order to simplify the problem, the authors identify the clinical scenarios of the newborn's shock to enhance the different pathogenetic moments and to build up appropriate therapeutic algorithms, without forgetting that at present there is no evidence that treatment of shock improves outcomes, despite the large amount of the studies conducted on this topic.

Bedside detection of low systemic flow in the very low birth weight infant on day 1 of life

We aimed to assess the relationship between the clinical and biochemical parameters of perfusion and superior vena cava (SVC) flow in a prospective observational cohort study of very low birth weight (VLBW) infants. Newborns with congenital heart disease were excluded. Echocardiographic evaluation of SVC flow was performed in the first 24 h of life. Capillary refill time (forehead, sternum and toe), mean blood pressure, urine output and serum lactate concentration were also measured simultaneously. Thirty-eight VLBW infants were examined. Eight patients (21%) had SVC flow less than 40 ml/kg/min. There was a poor correlation between the capillary refill time (in all sites), mean blood pressure, urine output and SVC flow. The correlation coefficient for the serum lactate concentration was r = -0.28, p = 0.15. The median serum lactate concentration was 3.5 (range 2.8-8.5) vs. 2.7 (range 1.2-6.9) mmol/l (p = 0.01) in low flow versus normal flow states. A serum lactate concentration of >2.8 was 100% sensitive and 60% specific for detecting a low flow state. Combining a capillary refill time of >4 s with a serum lactate concentration of >4 mmol/l had a specificity of 97% for detecting a low SVC flow state. Serum lactate concentrations are higher in low SVC flow states. A capillary refill time of >4 s combined with serum lactate concentrations >4 mmol/l increased the specificity and positive and negative predictive values of detecting a low SVC flow state.

Evaluation and treatment of hypotension in the preterm infant

A large proportion of very preterm infants receive treatment for hypotension. The definition of hypotension is unclear, and, currently, there is no evidence that treating it improves outcomes or, indeed, which treatment to choose among the available alternatives. Assessment of circulatory adequacy of the preterm infant requires a careful clinical assessment and may also require ancillary investigations. The most commonly used interventions, fluid boluses and dopamine, are problematic: fluid boluses are statistically associated with worse clinical outcomes and may not even increase blood pressure, whereas dopamine increases blood pressure mostly by causing vasoconstriction and may decrease perfusion. For neither intervention is there any reliable data showing clinical benefit. Prospective trials of intervention for hypotension and circulatory compromise are urgently required.

Low superior vena cava flow and effect of inotropes on neurodevelopment to 3 years in preterm infants

OBJECTIVE

The goal was to report the 1- and 3-year outcomes of preterm infants with low systemic blood flow in the first day and the effect of dobutamine versus dopamine for treatment of low systemic blood flow.

METHODS

A cohort of 128 infants born at <30 weeks of gestation underwent echocardiographic measurement of superior vena cava flow at 3, 10, and 24 hours of age. Forty-two infants with low superior vena cava flow (<41 mL/kg per minute) were assigned randomly to dobutamine or dopamine. Surviving infants underwent blinded neurodevelopmental assessments at corrected ages of 1 and 3 years.

RESULTS

Seventy-six of 87 surviving infants were seen at 1 year and 67 at 3 years. Forty-four infants had low superior vena cava flow. At 3 years, with adjustment for perinatal risk factors, death was predicted by low superior vena cava flow, lower gestational age, and low 5-minute Apgar score. Substantial reductions in the Griffiths General Quotient were associated with low superior vena cava flow and birth weight of <10th percentile. Infants with low flow had significant reductions in personal-social, hearing and speech, and performance subscales. Death or disability at 3 years was predicted by low superior vena cava flow and lower gestational age. For infants treated with inotropes, no significant differences were found in clinical outcomes, except for reduced rates of late severe periventricular/intraventricular hemorrhage in the dobutamine group. At 3 years, infants in the dopamine group had significantly more disability and a lower Griffiths General Quotient. At the latest time measured, however, combined rates of death or disability were similar.

CONCLUSIONS

Early low superior vena cava flow was associated with substantial rates of death, morbidity, and developmental impairments. No difference was found in combined rates of death and disability for infants assigned randomly to dopamine or dobutamine.

Left ventricular contractility in extremely premature infants in the first day and response to inotropes

The aim was to assess myocardial contractility in infants born <30 wk gestation developing low systemic blood flow (SBF) in the first day, and the effect of dobutamine versus dopamine. Superior vena cava (SVC) flow was used as a measure of SBF at 3, 10, and 24 h (n = 106). Infants with low SVC flow randomized to dopamine or dobutamine. Myocardial contractility was determined by the relationship between left ventricular (LV) mean velocity of circumferential fiber shortening (mVcfs) and wall stress. Infants who developed low SVC flow had significantly worse myocardial contractility at 3 h, but not 10 h. At 24 h, low-flow infants had lower than expected mVcfs for any given LV stress. In 37 infants randomized to inotrope, there was no significant difference in contractility at 10 microg/kg/min. At 20 microg/kg/min (n = 21), dopamine increased whereas dobutamine decreased LV stress. Infants on dobutamine had significantly lower than expected mVcfs for any given LV stress compared with infants on dopamine. Contractility was not improved by either inotrope at either dose. In conclusion, infants developing low SVC flow in the first day have worse myocardial contractility at 3 h. Neither inotrope increased contractility, but dopamine increased LV stress at 20 microg/kg/min.

Assessment and support of the preterm circulation

There are no clinical outcome data on which to base recommendations on how to assess and support the preterm circulation. Current standards are derived from an assumed proportionality between systemic and organ blood flow and mean blood pressure. Our study of central measures of systemic blood flow suggests preterm haemodynamics are more complex than this. Low systemic blood flow is common in the first 24 h after birth in very preterm babies and is not necessarily reflected by low blood pressure. The causes of this low systemic blood flow are complex but may relate to maladaptation to high extrauterine systemic (and sometimes pulmonary) vascular resistance. After day 1, hypotensive babies are more likely to have normal or high SBF reflecting vasodilatation. Empirically, inotropes that reduce afterload (such as dobutamine) may be more appropriate in the transitional period, while those with more vasoconstrictor actions (such as dopamine) may be more appropriate later on. Defining the haemodynamic in an individual baby needs both blood pressure and echocardiographic measures of systemic blood flow. Research in this area needs to move beyond just demonstrating changes in physiological variables to showing improvements in important clinical outcomes.

Intrauterine smoke exposure: a new risk factor for bronchopulmonary dysplasia?

OBJECTIVE

To evaluate the role of intrauterine smoke exposure and other variables on the development of bronchopulmonary dysplasia (BPD) in infants with birth weight < 1500 g (VLBW).

METHODS

This case-control study investigated 277 VLBW infants (141 cases, 136 controls) admitted at birth to neonatal intensive care unit and survived to discharge. A retrospective telephone interview provided detailed parental information supplementing clinical data. Logistic regression assessed the effects of birth weight < 1000 g, gestational age < 30 weeks (GA<30), respiratory distress syndrome (RDS), neonatal mechanical ventilation > 7 days (MV>7), patent ductus arteriosus (PDA), intrauterine smoke exposure > or = 3 months (ISE), and of parental history of asthma on BPD (oxygen dependency at 28 days with characteristic radiographic abnormalities) occurrence.

RESULTS

Including all variables, only GA<30, RDS and MV>7 were significantly associated with BPD. ISE did not contribute significantly to this model (odds ratio [OR] 1.94; 95% confidence interval 0.88-4.26). Excluding iatrogenic variable MV>7, GA<30, RDS, PDA and ISE (OR 2.21; 95% confidence interval 1.03-4.76) were significantly associated with BPD. Analyzing GA as a continuous variable, the OR was 0.63 for each additional week.

CONCLUSIONS

Prolonged mechanical ventilation, RDS and low gestational age were the major BPD determinants. Intrauterine smoke exposure seems to influence independently BPD development.

Volume expansion during neonatal intensive care: do we know what we are doing?

Although volume expansion is liberally used in newborn intensive care, we know little about its effects on hemodynamics or outcomes. Given appropriately to a truly hypovolemic baby, it can be life-saving, but the clinical diagnosis of hypovolemia is probably very inaccurate. We know that volume expansion has less effect on blood pressure than dopamine, and although it seems to produce immediate increases in systemic blood flow, we do not know for how long these increases are sustained. There is evidence to show that the routine use of volume expansion in preterm babies has no effect on outcome, and there is little evidence to support its routine use during resuscitation or the treatment of metabolic acidosis. Whether crystalloids or colloids are preferable is also unclear in newborns. In situations of concern related to circulatory compromise, if possible, define the hemodynamics echocardiographically. Otherwise, if in doubt, some volume should be given, although it is probably unwise to keep expanding the volume if this is not improving physiologic (blood pressure and heart rate) or echocardiographic systemic blood flow parameters.

Cardiocirculatory effects of patent ductus arteriosus in extremely low-birth-weight infants with respiratory distress syndrome

BACKGROUND

Cardiocirculatory effects of hemodynamically significant patent ductus arteriosus (hsPDA) have not been systematically studied in extremely low-birth-weight (ELBW) infants with respiratory distress syndrome (RDS). The objective of the present study was to evaluate the effects of hsPDA on the left ventricular output (LVO) and organ blood flows in ELBW infants with RDS.

METHODS

Extremely low-birth-weight infants (birth-weight <1000 g) treated with surfactant for RDS were studied by serial Doppler flow examinations. Doppler flow variables in 19 infants in whom hsPDA developed (hsPDA group) were compared with those in 19 infants without hsPDA matched for gestational age, birth-weight, and postnatal age (non-hsPDA group). All infants in the hsPDA group had pharmacologic closure of ductus arteriosus when hsPDA developed.

RESULTS

Before pharmacological closure of PDA, the hsPDA group had significantly higher LVO, lower blood flow volume of the abdominal aorta, and lower mean blood flow velocities in the celiac artery, superior mesenteric artery, and renal artery than the non-hsPDA group. These alterations in the hsPDA group reverted to the levels in the non-hsPDA group after the closure of PDA and had no deleterious effects on the cardiorespiratory status. No significant differences between the groups were found in mean blood flow velocities of the anterior cerebral artery throughout the study period.

CONCLUSION

These results indicate that although LVO is increased, the splanchnic and renal blood flows are decreased when hsPDA develops in ELBW infants with RDS. The effects of these alterations of LVO and organ blood flows on the cardiorespiratory course seem to be minor when early pharmacologic closure of PDA is done.

Low systemic blood flow in the preterm infant

Low systemic blood flow in the first hours after birth of a preterm infant is an often unrecognized complication. Traditional measures of cardiovascular adequacy used in the neonatal intensive care unit such as capillary refill time and blood pressure may not identify this problem. Longitudinal measurement of systemic blood flow demonstrates a falling off of blood flow in the first 6-12 h after birth, often to less than half of normal, before a gradual return to normal values by 24-48 h of age. Identification and appropriate treatment of this reduction in flow may assist in preventing some of the complications of prematurity.

Ductal shunting, high pulmonary blood flow, and pulmonary hemorrhage

OBJECTIVE

To describe the relationship among ductal shunting, estimated pulmonary blood flow, and pulmonary hemorrhage in very preterm infants.

STUDY DESIGN

A total of 126 babies born before 30 weeks' gestation (median gestation 27 weeks, range 23 to 29 weeks) underwent echocardiography at 5, 12, 24, and 48 hours of age; measurements included right and left ventricular output, superior vena cava flow, and color Doppler diameter of any ductal shunt. Pulmonary blood flow was derived from the sum of right ventricular output and estimated ductal shunt flow.

RESULTS

Twelve (9.5%) babies had a pulmonary hemorrhage at a mean age of 38 hours. Compared with the rest of the cohort, these 12 babies were less likely to have had antenatal steroids (59% vs 90%) and were less mature (26 weeks vs 27 weeks). At the echocardiogram closest to the pulmonary hemorrhage, 11 (92%) of the 12 babies had a significant patent ductus arteriosus >1.6 mm in diameter (median 2 mm, range 0.7 to 2.4 mm), and the median pulmonary blood flow was 326 mL/kg/min (range 210 to 598 mL/kg/min). These measurements were significantly higher than those found in the rest of the cohort in the same period (median duct diameter 0.5 mm [range 0 to 2.9 mm], median pulmonary blood flow 237 mL/kg/min [range 107 to 569 mL/kg/min]). At 5-hour echocardiography the babies with pulmonary hemorrhage had significantly larger diameter ducts but similar pulmonary blood flow.

CONCLUSIONS

Pulmonary hemorrhage in preterm babies is associated with significant ductal shunting and high estimated pulmonary blood flow.

Peripheral oxygenation in hypotensive preterm babies

Monitoring oxygenation in peripheral tissues of preterm babies may be useful in understanding the redistribution of blood flow during hypotension. Hemoglobin flow and venous saturation were measured in the forearm using near infrared spectroscopy with venous occlusion and were used to calculate fractional oxygen extraction, oxygen delivery, and oxygen consumption. Thirty ventilated preterm babies (median birth weight 976 g) were studied; 15 were hypotensive and 15 normotensive. Treatment for hypotension was dopamine alone (median dose 5 microg/kg/min) in eight cases, 4.5% human albumin solution (20 mL/kg) with dopamine in five cases, and only a blood transfusion (20 mL packed cells/kg) in two cases. There was a weak correlation between hemoglobin flow and mean arterial blood pressure (r = 0.40, p = 0.03). In hypotensive compared with normotensive babies, there was a significantly lower median hemoglobin flow (10.2 versus 20.2 micromol/100 mL/min, p = 0.0006), forearm oxygen delivery (37.8 versus 75.2 micromol/100 mL/min, p = 0.0008), and oxygen consumption (11.0 versus 23.9 micromol/100 mL/min, p = 0.006), but the fractional oxygen extraction (0.327 versus 0.306, p = 0.48) and the blood lactate concentration (1.22 versus 1.20 mmol/L, p = 0.44) were similar. Following treatment of hypotension, oxygen delivery (p = 0.02) and oxygen consumption (p = 0.04) increased to 64.2 and 21.7 micromol/100 mL/min, respectively, but fractional oxygen extraction (p = 0.81) and blood lactate concentration (p = 0.94) after treatment were unchanged. VO2 was variable in the forearm of human infants. It reduced when DO2 was low, and there was no evidence of tissue injury or switch to anaerobic metabolism. Measurements of peripheral tissue oxygenation seem to be of some value in understanding the pathophysiologic changes that occur with hypotension.

Changes in left ventricular diastolic filling patterns before and after the closure of the ductus arteriosus in very-low-birth weight infants

To evaluate serial changes in left ventricular diastolic filling patterns in preterm infants, we performed echocardiographic examinations in 18 very-low-birth weight infants and 20 fullterm infants before and after the closure of the ductus arteriosus. In the fullterm infants, the ductal closure induced significant decreases in the peak velocity and flow velocity integral of early diastole, first third filling fraction, and mitral stroke volume. In the preterm infants, by contrast, there were significant increases in the flow velocity integral of early diastole, first third filling fraction, and mitral stroke volume after the ductal closure. No differences following the ductal closure were found in the atrial phase of filling and peak filling rate normalized to stroke volume in either group. When the ductus arteriosus was open, essentially the same left-to-right shunting of the ductus arteriosus was detected in both preterm and fullterm infants, but the Doppler flow patterns of the patent foramen ovale were different: the fullterm infants had a single flow peak mainly during ventricular late systole and early diastole, but the preterm infants had two or three flow peaks with nearly equal amplitudes lasting from ventricular systole to diastole, which resembled the Doppler flow pattern of atrial septal defect. Only a faint Doppler flow signal of the foramen ovale was observed after the ductus arteriosus closed. Our results obtained from the preterms suggest that the left-to-right shunt through the foramen ovale may be one important factor to alter the Doppler transmitral filling patterns during the fetal to neonatal cardiovascular changes.

Relationship between blood pressure and cardiac output in preterm infants requiring mechanical ventilation

OBJECTIVE

To assess the contribution of cardiac output in determining the blood pressure of preterm infants and to identify other factors that may be important.

METHODS

Sixty-seven preterm infants requiring mechanical ventilation (median birth weight, 1015 gm: median gestational age, 28 weeks) underwent on echocardiographic study at on average age of 19 hours (range, 7 to 31 hours). Measurements taken included left ventricular ejection fraction, left and right ventricular outputs by means of pulsed Doppler and the diameter of both the ductal and atrial shunt jets with the use of color Doppler as a measure of the size of shunt. Simultaneous measurements of intraarterial blood pressures, mean airway pressure, and inspired fraction of oxygen were recorded.

RESULTS

After we allowed for the influence of ductal shunting, the correlation between the left ventricular output and mean arterial blood pressure was significant but weak (r = 0.38). There were infants with low blood pressures and normal cardiac outputs, and conversely there were infants with low cardiac outputs and normal blood pressure. The infants with a mean arterial blood pressure of less than 30 mm Hg had a significantly lower gestational age (27 vs 28 weeks), higher mean airway pressure (9.0 vs 7.0 cm H2O), larger ductal diameter (1.6 mm vs 0.7 mm) and a lower systemic vascular resistance (163 vs 184 mm Hg/L per minute per kilogram of body weight). Multilinear regression identified higher mean airway pressure and larger ductal diameter as significant negative influences on mean arterial blood pressure, with higher gestational age and higher left ventricular output as significant positive influences.

CONCLUSIONS

Normal blood pressure cannot necessarily be equated with normal systemic now. These data emphasize the importance of other influences, and in particular that of varying systemic vascular resistance, in the determination of blood pressure in preterm infants.

Early determinants of right and left ventricular output in ventilated preterm infants

One hundred and twenty ventilated preterm infants, birthweight < 1500 g, were examined within the first 36 hours with colour Doppler echocardiography, to determine the cardiorespiratory influences on right (RVO) and left ventricular output (LVO). Forty nine of these infants had three further daily scans. Measurements included left ventricular (LV) ejection fraction, Doppler determination of RVO and LVO, and ductal and interatrial shunt direction, velocity and colour Doppler diameter. Infants were grouped by respiratory disease severity: mild, mean FIO2 in first 24 hours < 0.5; moderate/severe, mean FIO2 < 0.5; and fatal, death resulting directly from acute respiratory distress. In the early studies ventricular outputs varied widely (RVO: 62-412 ml/kg/minute, LVO: 75-505 ml/kg/minute). The incidence of low ventricular outputs (< 150 ml/kg/minute) increased with worsening respiratory disease. The incidence of low RVO in the mild group was 19%, in the moderate/severe group 42%, and in the fatal group 85%. More infants had a low RVO than a low LVO, reflecting the impact of ductal shunting. Ductal and atrial shunting was predominantly left to right except in those with fatal respiratory disease. In those studied longitudinally, RVO and LVO increased with age and low outputs were not seen after day 3. Multilinear regression analyses, with RVO as the dependent variable, revealed increasing LVO and atrial shunt diameter as significant positive influences and increasing ductal shunt diameter and mean airway pressure as a significant negative influence. With LVO as the dependent variable, increasing RVO, ductal shunt diameter, and age were significant positive influences and increasing atrial shunt diameter was a significant negative influence. Low ventricular outputs are more common with worsening respiratory disease. Mean airway pressure and ductal shunting are two negative influences on ventricular outputs over which there is some therapeutic control.

Longitudinal changes in the diameter of the ductus arteriosus in ventilated preterm infants: correlation with respiratory outcomes

This study aimed to examine the early natural history of ductal shunting in ventilated preterm infants (< 1500 g) and to document the association between this shunting and respiratory outcomes. The size of the ductal shunt was assessed in 48 infants using serial echocardiographic measurement of colour Doppler internal ductal diameter and pulsed Doppler postductal aortic diastolic flow (PADF). At all postnatal ages, normal antegrade PADF was invariably seen when the ductal diameter was 1.5 mm or less, and was usually abnormal (absent or retrograde) when more than 1.5 mm. Longitudinal progress of ductal diameter fell into three groups: (i) asymptomatic spontaneous closure (n = 31)--in 20 of these infants closure occurred within 48 hours; (ii) symptomatic PDA which enlarged after a postnatal constriction (n = 9); and (iii) symptomatic PDA that showed minimal postnatal constriction (n = 8). Infants in group 2 were significantly less mature and had PDAs which became symptomatic significantly later than those in group 3. Logistic regression showed that ductal shunting had a significant correlation with mean oxygenation index over the first five days but not with ventilator or oxygen days. Gestation had the most significant association with the latter two variables, with atrial shunting also being related to days in oxygen. The preterm duct displays a wide spectrum of postnatal constrictive activity. Symptomatic PDAs usually showed slower early postnatal constriction. Ductal shunting independently related to short term but not long term respiratory outcomes.