Cardiovascular effects of patent ductus arteriosus in preterm lambs with respiratory distress

Patent ductus arteriosus and the risk of bronchopulmonary dysplasia-associated pulmonary hypertension

BACKGROUND

The aim of the study was to determine whether prolonged exposure to a moderate/large patent ductus arteriosus left-to-right shunt (PDA) increases the risk of late (beyond 36 weeks) pulmonary hypertension (BPD-PH) and pulmonary vascular disease (BPD-PVD) during the neonatal hospitalization in preterm infants (<28 weeks' gestation) with bronchopulmonary dysplasia (BPD).

METHODS

All infants requiring respiratory support ≥36 weeks had systematic echocardiographic evaluations for BPD-PH at planned intervals. Infants were classified as having either flow-associated BPD-PH (BPD-flow-PH) or BPD-PVD.

RESULTS

256 infants survived ≥36 weeks: 105 had NO BPD (were off respiratory support by 36 weeks); 151 had BPD. 22/151 had BPD-PH (12/22 had BPD-flow-PH from a PDA that persisted beyond 36 weeks; 10/22 had BPD-PVD). Moderate/large PDA shunts that persisted beyond 36 weeks were significantly associated with an increased incidence of BPD-PH due to BPD-flow-PH. We found no association between the duration of PDA exposure and the incidence of BPD-PVD.

CONCLUSIONS

Moderate/large PDA shunts increase the risk of flow-associated BPD-PH when present beyond 36 weeks. Although term infants with PDA-congenital heart disease can develop pulmonary vascular remodeling and PVD after months of PDA exposure, we found no echocardiographic evidence in preterm infants that prolonged PDA exposure increases the incidence of BPD-PVD during the neonatal hospitalization.

IMPACT

In our study, preterm infants (<28 weeks' gestation) with bronchopulmonary dysplasia (BPD) had a 15% incidence of pulmonary hypertension (PH) beyond 36 weeks' postmenstrual age as a comorbidity. Moderate/large patent ductus arteriosus (PDA) shunts increased the risk of flow-associated PH when present beyond 36 weeks. Although months of prolonged PDA exposure can cause pulmonary vascular remodeling and pulmonary vascular disease (PVD) in term infants with PDA-congenital heart disease, we found no echocardiographic evidence for an association between the duration of PDA exposure and the incidence of late PVD during the neonatal hospitalization in preterm infants with BPD.

Patent Ductus Arteriosus: A Contemporary Perspective for the Pediatric and Adult Cardiac Care Provider

The burden of patent ductus arteriosus (PDA) continues to be significant. In view of marked differences in preterm infants versus more mature, term counterparts (viewed on a continuum with adolescent and adult patients), mechanisms regulating ductal patency, genetic contributions, clinical consequences, and diagnostic and treatment thresholds are discussed separately, when appropriate. Among both preterm infants and older children and adults, a range of hemodynamic profiles highlighting the markedly variable consequences of the PDA are provided. In most contemporary settings, transcatheter closure is preferable over surgical ligation, but data on longer-term outcomes, particularly among preterm infants, are lacking. The present review provides recommendations to identify gaps in PDA diagnosis, management, and treatment on which subsequent research can be developed. Ultimately, the combination of refined diagnostic thresholds and expanded treatment options provides the best opportunities to address the burden of PDA. Although fundamental gaps remain unanswered, the present review provides pediatric and adult cardiac care providers with a contemporary framework in PDA care to support the practice of evidence-based medicine.

Patent ductus arteriosus management and the drift towards therapeutic nihilism - What is the evidence?

The published literature on patent ductus arteriosus (PDA) management is challenging to interpret due to poorly designed trials with high rates of open label treatments, homogenisation of patients with varying physiological subtypes, poor treatment efficacy, and spontaneous closure in more mature infants. The perceived lack of clinical benefit has led to a drift away from medical and surgical treatment of all infants with a PDA. This therapeutic nihilism as a default response to PDA management fails to recognise the physiological relevance of a left-to-right shunt with early haemodynamic instability after birth and subsequent pulmonary volume overload with prolonged exposure. Clinicians need to know if therapeutic nihilism is safe. This review will provide an overview of the available data on the efficacy of known PDA treatments, conservative management and supportive care measures that are currently applied.

Patent ductus arteriosus and cerebral, cardiac, and gut hemodynamics in premature neonates

Patent ductus arteriosus is associated with multiple comorbidities in premature infants, however a causal link or strategy to decrease these morbidities has not been found. The association between the patent ductus arteriosus and morbidities has biologic plausibility as, like any cardiac mixing lesion, a significant systemic to pulmonic shunt may lead to pulmonary over-circulation and systemic hypoperfusion. Understanding the underlying pathophysiology of associated morbidities in the setting of a patent ductus arteriosus may aid in risk stratifying infants and offer a patient targeted approach to infants with a pathological ductal shunt. While the deleterious impact of increased pulmonary blood flow maybe easier to identify, the impact on end-organ perfusion is more challenging. In this review, we will discuss the pathophysiology of a hemodynamically significant patent ductus arteriosus in premature infants, impact on end-organ perfusion and associated morbidities, and novel modalities to assess shunt volume and effect on end-organ perfusion.

PDA-TOLERATE Trial: An Exploratory Randomized Controlled Trial of Treatment of Moderate-to-Large Patent Ductus Arteriosus at 1 Week of Age

OBJECTIVE

To compare early routine pharmacologic treatment of moderate-to-large patent ductus arteriosus (PDA) at the end of week 1 with a conservative approach that requires prespecified respiratory and hemodynamic criteria before treatment can be given.

STUDY DESIGN

A total of 202 neonates of <28 weeks of gestation age (mean, 25.8 ± 1.1 weeks) with moderate-to-large PDA shunts were enrolled between age 6 and 14 days (mean, 8.1 ± 2.2 days) into an exploratory randomized controlled trial.

RESULTS

At enrollment, 49% of the patients were intubated and 48% required nasal ventilation or continuous positive airway pressure. There were no differences between the groups in either our primary outcome of ligation or presence of a PDA at discharge (early routine treatment [ERT], 32%; conservative treatment [CT], 39%) or any of our prespecified secondary outcomes of necrotizing enterocolitis (ERT, 16%; CT, 19%), bronchopulmonary dysplasia (BPD) (ERT, 49%; CT, 53%), BPD/death (ERT, 58%; CT, 57%), death (ERT,19%; CT, 10%), and weekly need for respiratory support. Fewer infants in the ERT group met the rescue criteria (ERT, 31%; CT, 62%). In secondary exploratory analyses, infants receiving ERT had significantly less need for inotropic support (ERT, 13%; CT, 25%). However, among infants who were ≥26 weeks gestational age, those receiving ERT took significantly longer to achieve enteral feeding of 120 mL/kg/day (median: ERT, 14 days [range, 4.5-19 days]; CT, 6 days [range, 3-14 days]), and had significantly higher incidences of late-onset non-coagulase-negative Staphylococcus bacteremia (ERT, 24%; CT,6%) and death (ERT, 16%; CT, 2%).

CONCLUSIONS

In preterm infants age <28 weeks with moderate-to-large PDAs who were receiving respiratory support after the first week, ERT did not reduce PDA ligations or the presence of a PDA at discharge and did not improve any of the prespecified secondary outcomes, but delayed full feeding and was associated with higher rates of late-onset sepsis and death in infants born at ≥26 weeks of gestation.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01958320.

Patent ductus arteriosus, its treatments, and the risks of pulmonary morbidity

A persistent left-to-right shunt through a patent ductus arteriosus (PDA) increases the rate of hydrostatic fluid filtration into the lung's interstitium, impairs pulmonary mechanics, and prolongs the need for mechanical ventilation. In preclinical trials, pharmacologic PDA closure leads to improved alveolarization and minimizes the impaired postnatal alveolar development that is the pathologic hallmark of bronchopulmonary dysplasia (BPD). Although routine prophylactic treatment of a PDA on the day of birth does not appear to offer any more protection against BPD than delaying treatment for 2-3 days, recent evidence from quality improvement trials suggests that early pharmacologic treatment decreases the incidence of BPD compared with a treatment approach that exposes infants to a moderate-to-large PDA shunt for the first 7-10 days after birth. After the first week, routine pharmacologic treatment (compared with continued PDA exposure) no longer appears to alter the course of BPD development. Evidence from epidemiologic, preclinical, and randomized controlled trials demonstrate that early ductus ligation is an independent risk factor for the development of BPD.

Circulatory Insufficiency and Hypotension Related to the Ductus Arteriosus in Neonates

The biological role of the ductus arteriosus (DA) in neonates varies from an innocent bystander role during normal postnatal transition, to a supportive role when there is compromise to either systemic or pulmonary blood flow, to a pathological state in the presence of hemodynamically significant systemic to pulmonary shunts, as occurs in low birth weight infants. Among a wide array of clinical manifestations arising due to the ductal entity, systemic circulatory insufficiency and hypotension are of significant concern as they are particularly challenging to manage. An understanding of the physiologic interplay between the DA and the circulatory system is the key to developing appropriate targeted therapeutic strategies. In this review, we discuss the relationship of systemic hypotension to the DA, emphasizing the importance of critical thinking and a precise individual approach to intensive care support. We particularly focus on the variable states of hypotension arising directly due to a hemodynamically significant DA or seen in the period following successful surgical ligation. In addition, we explore the mechanistic contributions of the ductus to circulatory insufficiency that may manifest during the transitional period, states of maladapted transition (such as acute pulmonary hypertension of the newborn), and congenital heart disease (both ductal dependent and non-ductal dependent lesions). Understanding the dynamic modulator role of the ductus according to the ambient physiology enables a more precise approach to management. We review the pathophysiology, clinical manifestations, diagnosis, monitoring, and therapeutic intervention for the spectrum of DA-related circulatory compromise.

Surgical Ligation for Patent Ductus Arteriosus in Extremely Premature Infants: Strategy to Reduce their Risk of Neurodevelopmental Impairment

Surgical ligation for patent ductus arteriosus (PDA) in extremely low birth weight infants (ELBWIs) has been shown a possible association with neurodevelopmental impairment (NDI) because of its invasiveness. However, we have undergone surgical ligation for ELBWIs immediately after cyclooxygenase inhibitor failed to close a hemodynamically significant PDA (hsPDA) to maintain proper systemic circulation. We aimed to determine the effect of surgical ligation for hsPDA on NDI in ELBWIs. In enrolled 71 ELBWIs, the clinical parameters, including the developmental quotient (DQ), were collected and compared among three groups that were divided by closure mode: spontaneous closure (n = 11), cyclooxygenase inhibitor therapy (n = 37) and surgical ligation (n = 23). No significant differences in DQ at the age of 36 months among the three groups were found: Median (interquartile range): 92.0 (31.0), 89.0 (22.0) and 92.0 (24.5), respectively. In a comparison between groups of DQ < 70 (n = 15) and DQ ≥ 70 (n = 56), a significant difference was found in the parameters related to prematurity (p < 0.05 for each): gestational age [23.9 (1.70) vs. 25.4 (2.50) weeks], birth weight [595 (183) vs. 714 (192) g], Apgar score < 5 (1 min) (67% vs. 36%), and laser photocoagulation for retinopathy of prematurity (73% vs. 43%), but there was no significant association with hsPDA. Therefore, we propose that surgical ligation for hsPDA in ELBWIs should be immediately carried out for preventing future neurodevelopmental deterioration if the cyclooxygenase inhibitor failed to close hsPDA.

Effects of Prophylactic Indomethacin on Vasopressor-Dependent Hypotension in Extremely Preterm Infants

OBJECTIVE

To determine whether a moderate-to-large patent ductus arteriosus (PDA) is responsible for vasopressor-dependent hypotension, occurring at the end of the first postnatal week.

STUDY DESIGN

We performed a retrospective, double cohort controlled study of infants delivered at ≤27+6 weeks' gestation (n = 313). From January 2004 through April 2011, all infants were treated with prophylactic indomethacin ([PINDO] epoch). From May 2011 through December 2015, no infant was treated with indomethacin until at least 8 postnatal days (conservative epoch). Echocardiograms were performed on postnatal days 6 or 7. Hypotension was managed by a predefined protocol. The primary outcome was the incidence of dopamine-dependent hypotension, defined as having received at least 6 µg/kg/min dopamine for at least 24 hours during postnatal days 4-7.

RESULTS

As expected, the incidence of moderate-to-large PDA at the end of the first week differed significantly between epochs (PINDO = 8%; conservative = 64%). In multivariate analyses, infants in the PINDO epoch had a significantly lower incidence of vasopressor-dependent hypotension (11%) than infants in the conservative epoch (21%; OR = 0.40, 95% CI 0.20-0.82). Infants in the PINDO epoch also required less mean airway pressure, had a lower respiratory severity score, and lower mode of ventilation score than infants in the conservative epoch during postnatal days 4-7. The effects of PINDO on both the incidence of vasopressor-dependent hypotension and the need for respiratory support were no longer significant when analyses were adjusted for "presence or absence of a moderate-to-large PDA."

CONCLUSION

PINDO decreases vasopressor-dependent hypotension and the need for respiratory support at the end of the first postnatal week. These effects are mediated by closure of the PDA.

Modeling of neonatal hemodynamics during PDA closure

The transition of the fetus at birth to extrauterine life is an extremely complex process. As part of the hemodynamic transition, the closure of ductus arteriosus, a fetal shunt, is among the key steps to achieve normal postnatal cardiovascular function. However, significant gaps remain in our knowledge pertaining to the hemodynamics of normal ductal closure, and in case of failure of closure, to the hemodynamic consequences and treatment of the patent ductus arteriosus (PDA) in preterm infants. This paper presents a mathematical model of a newborn's cardiovascular system with five peripheral organ systems, the ductus arteriosus, and the baroreceptor reflex. We present the hemodynamic findings during simulation of sudden ductal closure, an event seen in real life when the PDA is closed surgically. The results of our model match the clinical data.

Hemodynamic monitoring of the critically ill neonate: An eye on the future

By continuous assessment of dynamic changes in systemic and regional perfusion during transition to extrauterine life and beyond, comprehensive neonatal hemodynamic monitoring creates numerous opportunities for both clinical and research applications. In particular, it has the potential of providing additional details about physiologic interactions among the key hemodynamic factors regulating systemic blood flow and blood flow distribution along with the subtle changes that are frequently transient in nature and would not be detected without such systems in place. The data can then be applied for predictive mathematical modeling and validation of physiologically realistic computer models aiming to identify patient subgroups at higher risk for adverse outcomes and/or predicting the response to a particular perturbation or therapeutic intervention. Another emerging application that opens an entirely new era in hemodynamic research is the use of the physiometric data obtained by the monitoring and data acquisition systems in conjunction with genomic information.

Development of left ventricular longitudinal speckle tracking echocardiography in very low birth weight infants with and without bronchopulmonary dysplasia during the neonatal period

Objectives

In preterm infants, postnatal myocardial adaptation may be complicated by bronchopulmonary dysplasia (BPD). We aimed to describe the development of left ventricular function by serial 2D, Doppler, and speckle tracking echocardiography (2D-STE) in infants with and without BPD during the neonatal period and compare these to anthropometric and conventional hemodynamic parameters.

Study Design

Prospective echocardiography on day of life (DOL) 1, 7, 14, and 28 in 119 preterm infants <1500 g birth weight of whom 36 developed BPD (need for oxygen supplementation at 36 weeks gestational age). Non-BPD and BPD infants differed significantly in median (IQR) gestational age (25.5(24–26.5) weeks vs. 29(27–30) weeks, p<0.001) and birth weight (661(552–871) g vs. 1100(890–1290) g, p<0.001).

Results

The intra- and inter-observer variability of the 2D-STE parameters measured did not depend on time of measurement, although there were significant differences in the reproducibility of the parameters. Low intra- and inter-observer variability was seen for longitudinal systolic strain and strain rate mid septum with a median CV (coefficient of variation) of <4.6%. Much higher CVs (>10%) were seen for the apical segment. While anthropometric parameters show rapid development during the first 4 weeks of life, the speckle tracking parameters did not differ statistically significantly during the neonatal period. Infants with and without BPD differed significantly (p<0.001) in the development of anthropometric parameters, conventional hemodynamic parameters except for heart rate, and 2D-STE parameters: global longitudinal systolic strain rate (GLSSR) and longitudinal systolic strain for the mid left wall (LSSR). The largest differences were seen at DOL 1 and 7 in GLSSR (p<0.001) and in LSSR (p<0.01).

Conclusions

Reproducible 2D-STE measurements are possible in preterm infants <1500 g. Cardiac deformation reveals early (DOL 1 and 7) ventricular changes (GLSSR and LSSR) in very low birth weight infants who develop BPD.

Outcome of patent ductus arteriosus ligation in premature infants in the East of England: a prospective cohort study

BACKGROUND

Surgical ligation of patent ductus arteriosus is considered when medical treatment fails or is contraindicated. This study aims to determine the mortality and morbidity of preterm neonates referred for patent ductus arteriosus ligation.

METHODS

A prospective study was conducted in the East of England to follow the outcome of premature infants under 37 weeks’ gestation undergoing patent ductus arteriosus ligation. A standardised proforma was used to collect information before and after the procedure.

RESULTS

A total of 102 premature infants were recruited, and patent ductus arteriosus ligation was performed in 92. Surgical complications occurred in 8.7% (8/92), which included pneumothorax (5/8), recurrent laryngeal nerve palsy (2/8), and chylothorax (1/8). Morbidity outcome data were not available for all infants. The incidence of chronic lung disease was 88% (88/99); intraventricular haemorrhage was 49% (49/100); necrotising enterocolitis 39% (39/99), and retinopathy of prematurity 42% (41/97). The overall mortality rate in our study was 7.8% (8/102). Mortality rate in infants who had patent ductus arteriosus ligation was 4.3% (4/92). The 30-day survival rate after ligation was 99% (91/92). Beyond 30 days post-ligation, three infants died from other causes that were not directly related to surgery.

CONCLUSION

Patent ductus arteriosus ligation in premature infants is associated with low mortality and complication rates; however, there is a high incidence of neonatal morbidity. Surgical capacity for patent ductus arteriosus ligation needs to be carefully planned nationally as the duration of ‘‘waiting time’’ and transport to another surgical centre could adversely affect outcomes in this high-risk population.

Left ventricular efficiency after ligation of patent ductus arteriosus for premature infants

OBJECTIVE

The purpose of this study was to evaluate the hemodynamic changes in left ventricular function before and after patent ductus arteriosus ligation in premature infants with regard to the energetic efficiency of left ventricular pumping.

METHODS

Thirty-five premature infants who underwent patent ductus arteriosus ligation were enrolled in this study. Left ventricular efficiency was evaluated at 4 points: within 24 hours before patent ductus arteriosus ligation, within 24 hours after patent ductus arteriosus ligation, between postoperative days 2 and 4, and on postoperative day 7. The indices of contractility (end-systolic elastance) and afterload (effective arterial elastance) were approximated on the basis of the systemic blood pressure and systolic or diastolic left ventricular volume. The ratio of stroke work and pressure-volume area, representing the ventricular efficiency, was estimated using the following theoretic formula: the ratio of stroke work and pressure-volume area = 1/(1 + 0.5 ventriculoarterial coupling).

RESULTS

Left ventricular efficiency was transiently deteriorated within 24 hours after patent ductus arteriosus ligation because of the marked increase of the afterload and the slight increase of contraction, and then recovered to preoperation levels by 2 to 4 days after patent ductus arteriosus ligation.

CONCLUSIONS

Analysis of indices representing the afterload, contractility, and energetic efficiency of the left ventricle may provide practical information for the management of premature infants during the postoperative period after patent ductus arteriosus ligation.

Managing the patent ductus arteriosus in the premature neonate: a new look at what we thought we knew

Over recent years, the clinical approach to patency of the ductus arteriosus in the premature neonate has been the subject of intensive reevaluation. What had once been considered inherently obvious is no longer to be taken for granted. In this review we will focus on some of the controversies surrounding various aspects of the pharmacologic treatment regimens for patent ductus arteriosus closure. The pros and cons of prophylactic vs therapeutic indomethacin, of early vs late therapy, of high- vs low-dose indomethacin, of single vs multiple courses of treatment, and of ibuprofen vs indomethacin will be considered. In addition, the possibility that patency of the ductus arteriosus is merely a physiological manifestation of extreme prematurity, and thus does not necessarily need to be therapeutically closed, has become a viable approach in some cases. As such, we will examine echocardiographic and biochemical criteria aimed at determining the clinical and hemodynamic significance of ductal shunting, and thereby of the need to treat. Finally, we speculate on potential therapeutic directions for the future, including individualized treatment regimens and multidrug treatment cocktails for those who fail initial monodrug therapy.

The ductus arteriosus: a refined approach!

Although ongoing patency of the ductus arteriosus is common in small extremely preterm infants, consensus is lacking regarding its clinical significance and treatment strategies. Literature regarding likelihood of spontaneous closure, impact on neonatal morbidity and long-term outcomes, and adverse effects of intervention has led to uncertainty as to the best course of action. Enhancing the determination of hemodynamic significance and refining patient selection for therapeutic intervention will streamline the decision-making process. Targeted neonatal echocardiography performed by the clinician has gained popularity worldwide, and preliminary data show that it has the potential to optimize patient outcomes. We review the arguments for and against medical and surgical therapy, explore how targeted neonatal echocardiography used in conjunction with biomarkers may refine the treatment approach, and consider future directions in the field.

N-terminal-pro-brain natriuretic peptide: a guide for early targeted indomethacin therapy for patent ductus arteriosus in preterm Infants

AIM

To determine whether N-terminal-pro-brain natriuretic peptide (NT-proBNP) level could be an effective guide for early targeted indomethacin therapy for patent ductus arteriosus (PDA) in preterm infants.

METHODS

An interventional study involved preterm infants, born at <33 weeks of gestation, who had plasma NT-proBNP levels obtained at day 2 of life. Indomethacin therapy was given if plasma NT-proBNP level was ≥10,180 pg/mL, the cut-off for predicting hemodynamic significant PDA (hsPDA). Echocardiograms were performed within 6 h at the time of plasma NT-proBNP collection and again at day 7, or whenever clinical hsPDA was suspected. Primary outcomes were the incidence of later hsPDA and unnecessary exposure rate to indomethacin.

RESULTS

Fifty infants were enrolled. On day 2, 19 (38%) infants had plasma NT-proBNP above the cut-off and received indomethacin therapy; none of them developed later hsPDA, while 1 of 31 infants with NT-proBNP below the cut-off level developed clinical hsPDA. Unnecessary exposure to indomethacin occurred in two infants (11%). Overall, no enrolled infants had either reopening of ductus or PDA ligation.

CONCLUSION

Using NT-proBNP level on day 2 as a guide for early targeted indomethacin therapy reduced later onset of hsPDA and the number of unnecessary exposures to indomethacin.

Patent ductus arteriosus in the preterm infant: to treat or not to treat?

Pharmacological and/or surgical closure of a hemodynamically significant patent ductus arteriosus (PDA) in the very preterm infant has been the standard of care over the past few decades. However, the rationale for closure of PDA has recently been challenged. In this article, the factors that have fueled the controversy of the approach to the management of PDA and the gap in our knowledge are reviewed in detail. In addition, the pros and cons of the different treatment strategies applied in clinical care are evaluated with a focus on discussing the available evidence in the literature.

Microcirculation in preterm infants: profound effects of patent ductus arteriosus

OBJECTIVES

To assess potential effects of a hemodynamically significant persistent ductus arteriosus (sPDA) in the skin microcirculation in preterm neonates.

STUDY DESIGN

In 25 patients (<32 weeks of gestation; birth weight <1250 g) with sPDA (n = 13) or no significant PDA (non-sPDA; n = 12) functional vessel density and vessel diameters were investigated prospectively. Sidestream dark field imaging was performed in the skin of both arms from the third day of life until PDA closure or until day 7 or 8 for the non-sPDA group.

RESULTS

Before PDA treatment, functional vessel density was significantly lower in the sPDA group compared with the non-sPDA group. In the sPDA group, there were significantly fewer large vessels (diameter >20 microm) and significantly more small vessels (diameter <10 microm). After successful PDA treatment, these differences disappeared. In both groups, functional vessel density differed significantly between the left and right arm, persisting even after successful treatment. Regression analysis showed an inverse linear correlation between the hemodynamic echocardiographic findings and functional vessel density (P <.005).

CONCLUSION

sPDA causes major changes in the microcirculation of premature neonates; functional vessel density is reduced, with a shift in perfusion from larger toward smaller vessels. The redistribution of flow might be a compensatory mechanism to preserve physiologic metabolism.

[Patent ductus arteriosus in premature infants]

BACKGROUND

Patent ductus arteriosus in premature infants has often been treated because of its association with worsening of pulmonary disease and complications such as bronchopulmonary dysplasia. This view has now been challenged.

MATERIAL AND METHODS

Relevant publications have been identified from review articles in international peer-reviewed journals. The articles have been retrieved through searches in the PubMed and Cochrane-databases.

RESULTS

Recent research has led to a new understanding of patent ductus arteriosus - a shift of paradigm has occurred. The condition implies that a shunt enables blood to flow from right to left in the first postnatal days (when pulmonary arterial pressure is high), and left to right in cases where significant pulmonary disease is present. The increased pulmonary blood flow improves oxygenation, and the condition should be considered as physiological in small premature infants. A patent ductus arteriosus does not worsen concomitant pulmonary disease or increase the risk of bronchopulmonary dysplasia, intraventricular hemorrhage, necrotising enterocolitis or other complications.

INTERPRETATION

Treatment of a patent ductus arteriosus with COX-inhibitors such as indomethacin and ibuprofen, increases the risk for bronchopulmonary dysplasia without reducing other complications or death. A large patent ductus arteriosus has significant hemodynamic effects and should be treated with fluid restriction, diuretics and inotropic drugs before closure is considered. Surgical closure of a patent ductus arteriosus is linked to neurosensory impairment in survivors.

Pathophysiology of patent ductus arteriosus in premature neonates

Failure of complete postnatal closure of the ductus arteriosus is associated with various neonatal morbidities. Functional closure resulting from smooth muscle constriction and permanent anatomic closure due to vascular remodeling are the results of a complex interaction of different mechanisms. Prostaglandins, oxygen, nitric oxide and various other factors play a key role in ductal closure. An understanding of the role of these factors, involved both in maintenance of vascular tone of the ductus in fetal life as well as stimulation of ductal closure in postnatal life, and the cardiovascular and respiratory consequences of a patent ductus arteriosus, is important for the clinician involved in management of premature neonates.

Failure of ductus arteriosus closure is associated with increased mortality in preterm infants

OBJECTIVE

Because the standard of care has been to attempt to close the patent ductus arteriosus in preterm neonates, there is a paucity of information on the outcome of patients with a persistent patent ductus arteriosus. Our objective was to compare the mortality of preterm infants with and without a persistent patent ductus arteriosus.

METHODS

This was a single-center, retrospective study. Very preterm infants (birth weight < or = 1500 g and gestational age < or = 29 weeks) who survived beyond the first 3 postnatal days and did not undergo surgical ligation were included in the primary analysis. Mortality of neonates with a persistent and a closed patent ductus arteriosus was compared during the initial hospitalization by using the chi(2) test. Cox proportional hazard regression and logistic regression were used to take into account the time until death and assess the independent effect of each risk factor on mortality. We also performed 3 secondary analyses by excluding patients who died during the first 7 and 14 postnatal days and including patients who underwent surgical ligation by using different group assignments. A persistent patent ductus arteriosus was defined as a failure of either spontaneous or pharmacologic ductal closure during the initial hospitalization.

RESULTS

Patients with a persistent patent ductus arteriosus (n = 41) had lower birth weight and were less mature than those with a closed ductus (n = 260). Unadjusted mortality rate was higher in patients with a persistent (70.7%) than with a closed (11.2%) ductus. After adjustment for perinatal factors, level of maturity, disease severity, and morbid pathologies, the hazard for death in neonates with a persistent ductus was eightfold higher than in those with a closed ductus. Exclusion of patients who died during the first 2 weeks or inclusion of those who underwent ductal ligation did not change the findings.

CONCLUSION

Failure of ductal closure is associated with an increase in mortality in very preterm infants.

Effects of a patent ductus arteriosus on postprandial mesenteric perfusion in premature baboons

BACKGROUND

Superior mesenteric artery flow increases after a feeding to meet the intestines' increased metabolic demands. Although a patent ductus arteriosus can affect superior mesenteric artery perfusion in nonfeeding infants, there is no information about its effects on the hyperemic response that follows a feeding.

OBJECTIVE

Our goal was to study the effects of a patent ductus arteriosus on superior mesenteric artery perfusion in preterm baboons.

DESIGN

Preterm baboons were delivered at 67% gestation and ventilated for 14 days. Enteral feedings were begun and advanced per protocol. Feeding studies were performed between days 10 and 14. Thirty-one studies were performed in animals with a closed ductus; 21 studies in those with a moderate patent ductus arteriosus shunt (pulmonary-to-systemic blood flow ratio>or=2:1). Two-dimensional echocardiographic and Doppler examinations were performed before and 10 and 30 minutes after a feeding. The groups were similar in birth weights, feeding volumes, and age at time of study.

RESULTS

During the preprandial period, baboons with a moderate patent ductus arteriosus had significantly lower blood pressures and systemic blood flows than animals with a closed ductus. Preprandial superior mesenteric artery-blood flow velocities did not differ between the open and closed ductus groups. Animals with a closed ductus increased their superior mesenteric artery-velocities (diastolic and mean) and decreased their superior mesenteric artery relative-vascular-resistance (mean blood pressure/mean superior mesenteric artery-velocity) by 10 minutes after the feeding. By 30 minutes after the feeding, the values were returning to their preprandial values. In contrast, in baboons in the patent ductus arteriosus group, there were no significant changes in superior mesenteric artery-velocity or resistance after the feeding, and superior mesenteric artery-velocities were significantly lower than those in the closed ductus group.

CONCLUSIONS

A moderate patent ductus arteriosus shunt limits the ability of the preterm newborn baboon to increase its postprandial mesenteric blood flow velocity. We speculate that this may interfere with its ability to meet increased intestinal metabolic demands and may contribute to feeding difficulties.

Mechanisms regulating the ductus arteriosus

A patent ductus arteriosus (PDA) results in increased pulmonary blood flow and redistribution of flow to other organs. Several co-morbidities (i.e., necrotizing enterocolitis, intracranial hemorrhage, pulmonary edema/hemorrhage, bronchopulmonary dysplasia, and retinopathy) are associated with the presence of a PDA, but whether or not a PDA is responsible for their development is still unclear. In this review, comparative physiology between the full term and preterm newborn and the barriers preventing the necessary cascade of events leading to permanent constriction of the PDA are reviewed.

Effect of ductus ligation on cardiopulmonary function in premature baboons

RATIONALE

The role of the patent ductus arteriosus in the development of chronic lung disease in surfactant-treated premature newborns remains unclear.

OBJECTIVE

To examine the effects of ductus ligation on cardiopulmonary function and lung histopathology in premature primates.

METHODS

Baboons were delivered at 125 d, (term = 185 d) treated with surfactant, and ventilated for 14 d. Serial echocardiograms and pulmonary function tests were performed. Animals were randomized to ligation (n = 12) or no ligation (controls, n = 13) on Day 6 of life. Necropsy was performed on Day 14.

RESULTS

Compared with nonligated control animals, ligated animals had lower pulmonary-to-systemic flow ratios, higher systemic blood pressures, and improved indices of right and left ventricular performance. The ligated animals tended to have better compliance and ventilation indices for the last 3 d of the study. There were no differences between the groups in proinflammatory tracheal cytokines (interleukin [IL] 6 and IL-8), static lung compliance, or lung histology.

CONCLUSION

Although a persistent patent ductus arteriosus results in diminished cardiac function and increased ventilatory requirements at the end of the second week of life, ligation on Day 6 had no measurable effect on the histologic evolution of chronic lung injury in this 14-d baboon model.

The hemodynamic effects of neonatal patent ductus arteriosus shunting on superior mesenteric artery blood flow

OBJECTIVE

To determine if the ratio of the pulsatility index (PI) of the left pulmonary artery to the PI of the descending aorta, the Rp/Rs index, correlates with the degree of ductal steal from the intestine in neonates with a patent ductus arteriosus (PDA).

STUDY DESIGN

Echocardiograms and Doppler studies of the superior mesenteric artery (SMA) were performed in 41 neonates less than 35 weeks gestational age with a hemodynamically significant PDA (hsPDA).

RESULTS

There was a significant negative correlation between the Rp/Rs index and the SMA PI after controlling for ductal size (r=-0.476, p<0.008).

CONCLUSIONS

The Rp/Rs index can be used as an indicator of ductal steal on intestinal blood flow. The Rp/Rs index may be a useful adjunct to existing and new techniques for improving early assessment and treatment of hsPDA, and for evaluating the effects of hsPDA on systemic organs.

Pulmonary hypertension and right ventricular dysfunction in growth-restricted, extremely low birth weight neonates

This case series reports an acute episode of hypoxemia and systemic hypotension in seven infants under 1 kg, taking place several hours or days after birth, after a period of stability and in the absence of significant lung disease. These patients were growth-restricted at birth and had a history of chronic fetal hypoxia and oligohydramnios. Pulmonary hypertension and right ventricular dysfunction were found by echocadiography. Right ventricular ejection fraction was significantly depressed during the acute episode, compared to baseline values measured after recovery. The timing of symptoms seemed related to ductus arteriosus closure or constriction. Oxygenation and right ventricular function improvement occurred within a few days under ventilatory and inotropic support, while milrinone was administered in five cases. In conclusion, pulmonary hypertension is a rare but significant cause of hypoxemia in preterm infants, and pulmonary vasodilator therapy should be considered in the presence of right ventricular dysfunction.

Patent ductus arteriosus, indomethacin and necrotizing enterocolitis in very low birth weight infants: a population-based study

BACKGROUND

Patent ductus arteriosus is a risk factor for the development of necrotizing enterocolitis. The use of indomethacin to treat patent ductus arteriosus in preterm infants may either decrease the incidence of necrotizing enterocolitis by stabilizing or closing the ductus arteriosus or increase its incidence by a direct constricting effect on mesenteric blood vessels. The authors sought to evaluate the interrelationship between patent ductus arteriosus, treatment with indomethacin and the risk of necrotizing enterocolitis in very low birth weight infants.

METHOD

The Israel National database includes prospectively collected data on 99% of all very low birth weight infants in Israel. The study population comprised 6146 infants of 24-34 weeks' gestation born between 1995 and 2000. The effect of patent ductus arteriosus on necrotizing enterocolitis was assessed using multiple regression analysis.

RESULTS

Necrotizing enterocolitis occurred in 5.5% (n = 343) of all infants, in 9.4% of infants with patent ductus arteriosus and in 8.9% of infants who received indomethacin. The occurrence of necrotizing enterocolitis was independently associated with the presence of patent ductus arteriosus among infants not treated with indomethacin (odds ratio, 1.85) and those who received indomethacin therapy (odds ratio, 1.53). Indomethacin therapy in absence of patent ductus arteriosus was not associated with an increased risk of necrotizing enterocolitis (odds ratio, 0.72).

CONCLUSIONS

Patent ductus arteriosus is an independent risk factor for the development of necrotizing enterocolitis in very low birth weight infants. Therapy with indomethacin did not have a significant effect on the risk for necrotizing enterocolitis.

Measurement of the ductal L-R shunt during extracorporeal membrane oxygenation in the lamb

OBJECTIVE

In neonates, initially a ductal shunt is often observed during veno-arterial extracorporeal membrane oxygenation (ECMO). Depending on the degree of pulmonary hypertension in these patients, the ductal shunt will be right to left (R-L), left to right (L-R), or bidirectional. A ductal L-R shunt will possibly lead to pulmonary hyperperfusion and interact with ECMO weaning. The aim of this study was to give more insight in this ductal L-R shunt during ECMO by quantification of this shunt in relation to cardiac output and ECMO flow.

METHODS

In 7 lambs, closure of the duct was prevented by infiltration of the ductal wall with 10% formaline. This patent duct could be closed using a vesselloop around the duct. Ultrasound flowprobes were installed around the pulmonary artery, ascending aorta, and around the ECMO circulation tube. Right and left ventricular output and ECMO flow were measured. Ductus flow was defined as ductal left to right shunt (Qduct L-R) = flow in ascending aorta (Qao) - flow in central pulmonary artery (Qpa) and Qduct R-L = Qpa = Qao.

RESULTS

In 6 of 7 lambs a ductal L-R shunt was observed with a mean shunt of 44% (range, 11 to 79) of left ventricular output (Qduct L-R/Qao). Comparison with ECMO flow (Qduct L-R/Qecmo) showed a mean shunt of 76% (range 15 to 230). When compared with the total systemic circulating volume (Qpa + flow in the ECMO circuit [Qecmo]), the mean ductal L-R shunt showed a percentage of 51% (range, 7% to 142%).

CONCLUSIONS

During ECMO, mostly a ductal L-R shunt is observed in this lamb model. This ductal shunt is hemodynamically important. The percentages of this shunt in comparison with left ventricular output, and total circulating volume will support the idea that a ductal L-R shunt during ECMO could be another deteriorating factor in the often critical circulation of the neonate on veno-arterial ECMO.

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.

Beat-to-beat blood pressure variability and patent ductus arteriosus in ventilated, premature infants

The aim of the present study was to test the hypothesis that a relationship exists between respiratory-induced blood pressure variability (BPV) and transductal shunting in premature infants with respiratory distress. Ten premature infants (27-32 weeks gestation) with respiratory distress ventilated in the synchronised, positive-pressure mode were examined. The interrelations between blood pressure and transthoracic impedance were described using time and frequency domain analysis. Haemodynamic effects of left-to-right transductal shunting were assessed using Doppler echocardiography (ratio of diastolic flow to systolic flow in the subdiaphragmatic aorta). The dependence of blood pressure fluctuations on the respiratory cycle was seen consistently in both time-domain and cross-spectral analysis. The amplitude of these fluctuations varied between infants. In the time domain, the beat-to-beat pressure difference was 0.69-4.1 mmHg for diastolic and 0.99-5.24 mmHg for systolic blood pressure. There was a positive linear relationship between the respiratory-related BPV indicators and the extent of left-to-right transductal shunting ( r=0.86 for diastolic and 0.80 for systolic pressure, P<0.01). Respiratory-related BPV was not correlated to the indicators of left ventricle preload. It is concluded that respiratory related BPV involves both diastolic and systolic blood pressure and is correlated to the magnitude of left-to-right transductal shunting in the population studied.

Blood pressure in the very low birth weight neonate

Few aspects of management of very low birth weight (VLBW; <1500 g) neonates have generated as much controversy as the assessment of blood pressure (BP) and need for treatment of perceived abnormalities of this physiologic variable. The approach to this problem may differ greatly among various institutions and even among clinicians within a given center. The purpose of this manuscript is to review available information regarding physiologic determinants and measurement of BP in VLBW neonates, normative data for BP, clinical factors that may affect BP in these at-risk neonates and studies in which presumed abnormalities of BP resulted in adverse clinical outcomes. Options for treatment of low BP in VLBW neonates also will be discussed.

Early versus late indomethacin treatment for patent ductus arteriosus in premature infants with respiratory distress syndrome

OBJECTIVE

To compare efficacy and side effects of early versus late indomethacin treatment for patent ductus arteriosus (PDA) in premature infants.

METHODS

One hundred twenty-seven neonates receiving ventilatory assistance (gestational age: 26-31 weeks) with PDA confirmed by echocardiography were randomly assigned in a prospective multicenter trial to either early (day 3, n = 64) or late (day 7, n = 63) intravenous indomethacin treatment (3 x 0.2 mg/kg every 12 hours). Treatment history and side effects were registered.

RESULTS

The PDA closure rate was higher in the early treatment group at both 6 (73% vs 44%, P =.0008) and 9 days of age (91% vs 78%, P =.047). However, there was no significant difference in PDA ligation. Urine output was significantly lower (P <.0001), serum creatinine level was higher (P =.016), and more indomethacin courses were administered in the early treatment group (70 vs 26). Respiratory support, number of deaths, and intraventricular hemorrhages were similar in both groups. However, on the whole, major adverse events (death, necrotizing enterocolitis, and/or localized perforation, extension of hemorrhage, or cystic leukomalacia) occurred more frequently in the early treatment group (P =.017).

CONCLUSION

Early indomethacin treatment improves PDA closure but is associated with increased renal side effects and more severe complications and has no respiratory advantage over late indomethacin administration in ventilated, surfactant-treated, preterm infants <32 weeks' gestational age.

Lactate kinetics at rest and during exercise in lambs with aortopulmonary shunts

In a previous study [G. C. M. Beaufort-Krol, J. Takens, M. C. Molenkamp, G. B. Smid, J. J. Meuzelaar, W. G. Zijlstra, and J. R. G. Kuipers. Am. J. Physiol. 275 (Heart Circ. Physiol. 44): H1503-H1512, 1998], a lower systemic O2 supply was found in lambs with aortopulmonary left-to-right shunts. To determine whether the lower systemic O2 supply results in increased anaerobic metabolism, we used [1-13C]lactate to investigate lactate kinetics in eight 7-wk-old lambs with shunts and eight control lambs, at rest and during moderate exercise [treadmill; 50% of peak O2 consumption (VO2)]. The mean left-to-right shunt fraction in the shunt lambs was 55 +/- 3% of pulmonary blood flow. Arterial lactate concentrations and the rate of appearance (Ra) and disappearance (Rd) of lactate were similar in shunt and control lambs, both at rest (lactate: 1, 201 +/- 76 vs. 1,214 +/- 151 micromol/l; Ra = Rd: 12.97 +/- 1.71 vs. 12.55 +/- 1.25 micromol. min-1. kg-1) and during a similar relative workload. We found a positive correlation between Ra and systemic blood flow, O2 supply, and VO2 in both groups of lambs. In conclusion, shunt lambs have similar lactate kinetics as do control lambs, both at rest and during moderate exercise at a similar fraction of their peak VO2, despite a lower systemic O2 supply.

Early ductal shunting and intraventricular haemorrhage in ventilated preterm infants

AIM

To establish if there is an association between early cardiovascular adaptation and intraventricular haemorrhage (IVH).

METHODS

One hundred and seventeen ventilated preterm infants (mean gestational age 27 weeks, mean birthweight 993 g) were studied echocardiographically within the first 36 hours. Measurements included right (RVO) and left ventricular outputs (LVO), ductus arteriosus (PDA) and atrial shunt diameter using colour Doppler and pulsed Doppler direction and velocity of both shunts. Clinical variables collected over the first 24 hours included use of antenatal steroids, respiratory severity, and mean blood pressure. Cerebral ultrasound scans were reported by a radiologist blinded to clinical and echocardiographic data.

RESULTS

Antenatal steroids (two doses) had been given to 73% of the 86 infants with no IVH compared with 48% of the 21 infants with grades 1 and 2 IVH, and just 10% of 10 babies with grades 3 and 4 (P < 0.05). Both groups with IVH had significantly larger PDA diameters than the group with no IVH. Infants with grades 3 and 4 IVH had significantly lower RVO than the other infants. These differences were more pronounced when only infants with definite late IVH were analysed. Logistic regression analysis showed lack of antenatal steroids and larger PDA diameters were significantly associated with any grade of IVH and lack of antenatal steroids; lower RVO was significantly associated with grades 3 and 4 IVH.

CONCLUSIONS

Larger early PDA shunts, lower RVO, and lack of antenatal steroids were significantly associated with IVH.

Hemodynamics of respiratory failure in rabbit model: effect of surfactant supplementation

In some infants, administration of surfactant has been associated with an acute decrease in blood pressure. We hypothesized that independent of patent ductus arteriosus, low blood volume sensitizes to a negative hemodynamic response to surfactant supplementation. Respiratory failure was induced by bronchoalveolar lavage (BAL) in 30 young rabbits that were paralyzed and ventilated using tidal volumes of 10 ml/kg. After BAL, 15 ml/kg blood was withdrawn while the same volume of one of the following was infused: Ringer's lactate (n = 12); 5% albumin (n = 5); or leukocyte-free red blood cells (RBC, n = 6). The controls were not phlebotomized (n = 7). After blood withdrawal and transfusion, natural surfactant was given (100 mg/kg). The blood volume and pulmonary capillary leak were calculated. Cardiac output (CO) and vascular resistances were measured (Ringer's lactate; n = 5; controls, n = 4). Blood withdrawal and replacement had no immediate effect on either lung function or hemodynamics. Surfactant supplementation improved the gas exchange in all but the albumin-treated animals that had increased protein concentration in epithelial lining fluid. In the Ringer's lactate group, there was a 35% decrease (p < 0.05) in blood pressure, a 28% decrease (p < 0.05) in CO, and a 54% increase (p < 0.05) in pulmonary vascular resistance, shortly after surfactant administration. In the other groups, there was either a transient (controls) or no (RBC and albumin groups) decrease in blood pressure. The total blood volume and the intrapulmonary blood volume were lower in the Ringer's lactate group than in the RBC group. According to the present results, blood pressure and CO may decrease acutely when exogenous surfactant is administered coincidental with blood loss.

Bisferiens peaks in the radial artery pressure wave during patent ductus arteriosus in newborn infants: relationship with ascending aortic flow

Previously, we found evidence that bisferiens peaks in the radial artery pressure wave in the newborn infant may suggest the presence of a left-to-right shunt through a patent ductus arteriosus (PDA). The purpose of the present study was to analyze the origin of this pulsus bisferiens. Starting from the assumption that the radial artery pressure wave form is similar to the aortic pressure wave form, as described previously, we attempted to explain the bisferiens peaks on the basis of echocardiographically obtained ascending aortic flow. We studied 11 preterm mechanically ventilated infants with a left-to-right shunt through a PDA and 7 without. Aortic volume flow was established echocardiographically, and radial artery blood pressure measurement was performed with a high fidelity cathetermanometer system. Ascending aortic peak flow during PDA was significantly higher in the case of PDA, compared with the case without PDA. An augmented peak flow with an abrupt decline after the high peak in PDA, resulting in a sharp pressure peak with a steep decline after the peak, was thought to explain the first sharp peak of pulsus bisferiens. An abrupt decline of flow after peak flow is thought to be due to the fast runoff of blood through the ductus. According to the pulsatile pressure dynamics theories, which state that pressure wave forms consist of forward and backward wave forms, the second peak of the pulsus bisferiens can be explained by the return of the reflected (backward) wave form when the forward wave form has already considerably decreased. We conclude that the bisferiens peaks found in PDA result from a combination of large stroke volume (augmented first peak) and large runoff (quick decline of the forward wave) before the return of the reflected wave.

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.

[Influence of surfactants on hemodynamics during neonatal respiratory distress syndrome]

The neonatal respiratory distress syndrome tends to delay the circulatory adaptation to extra-uterine life and leads to systematic hypotension. Haemodynamic changes following the instillation of surfactant are not stereotyped. They depend on the type of surfactant, the time of the instillation, the degree of prematurity, the severity of the respiratory disease and the mode of instillation. They are characterized by a transient haemodynamic instability with variable consequences on arterial pressure and systemic blood flow. The use of surfactant tends to decrease pulmonary arterial resistances and pulmonary arterial pressures but this effect is variable and is not obviously accompanied by long-term deleterious effect on the arterial duct. Haemodynamics and blood gases changes due to surfactant instillation have a variable effect on cerebral blood flow. The potential role of blood gas and haemodynamics changes on the occurrence of pulmonary haemorrhage or cerebral damage following instillation of surfactant remains poorly established but has to be taken into account.

Prophylaxis of respiratory distress syndrome by treatment with modified porcine surfactant at birth: a multicentre prospective randomized trial

The objective of this prospective, multicentre trial, carried out at 18 third level hospitals in Italy, was to evaluate efficacy of modified porcine surfactant (Curosurf), administered at birth to prevent the development of respiratory distress syndrome (RDS) in premature infants. 287 babies with a gestational age of 24-30 weeks were randomized to prophylactic treatment with Curosurf (80 mg/ml; dose 20 mg/kg) or to a control group receiving no surfactant treatment in the delivery-room. Babies in both groups were eligible for rescue treatment with surfactant (200 mg/kg) if they developed clinical symptoms of RDS and required mechanical ventilation. The main end-point was to obtain, in the prophylaxis group, a 30% reduction in the incidence of grade 3-4 RDS. Median gestational age was 28 weeks in both groups and mean birth weight 1010 and 1002 g, respectively for prophylaxis and control babies. There was a 32% reduction in the incidence of grade 3-4 RDS in the prophylaxis group (p < 0.05). This was associated with a significant reduction in mean maximum fraction of inspired oxygen (0.57 vs 0.66%; p < 0.01), a decreased incidence of pulmonary interstitial emphysema (7 vs 14%; p < 0.05) and a lowered mortality (21 vs 35%; p < 0.01). Combined unfavourable outcome (mortality + bronchopulmonary dysplasia and/or grade 3-4 intraventricular hemorrhage and/or grade 2-4 retinopathy of prematurity) was significantly lower in the prophylaxis than in the second group (41 vs 58%; p < 0.01). The favourable effects of prophylactic treatment were equally recorded in all the age groups, including the babies with the lowest gestational age (24-25 weeks). Multiple and logistic regression analysis confirmed that high gestational age and surfactant prophylaxis were, independently, associated with a lower degree of RDS (p = 0.0001 and p = 0.0008, respectively) and a lower mortality (p = 0.0001 and p = 0.0045, respectively). We conclude that prophylaxis with modified natural surfactant effectively prevents RDS in newborn babies between 24 and 30 weeks' gestation.

Effect of ductal patency on organ blood flow and pulmonary function in the preterm baboon with hyaline membrane disease

OBJECTIVE

To examine the effect of early ductal ligation vs. maintenance of ductal patency on vital organ perfusion and pulmonary function in premature baboons with hyaline membrane disease.

DESIGN

Randomized, controlled interventional study to compare early ligation with formalin infiltration of the ductus arteriosus.

SETTING

Animal care facility at a dedicated research foundation.

SUBJECTS

Eighteen premature baboons delivered by hysterotomy at 140 +/- 2 day gestation.

INTERVENTION

Nine premature baboons underwent formalin infiltration of the ductus arteriosus (group 1), and nine underwent ductal ligation (group 2). Surgical ligation or formalin infiltration was performed at 2 to 4 hrs of age. Animals were maintained on mechanical ventilation and ventilator parameters were adjusted to maintain PaO2 and PaCO2 within the physiologic range.

MAIN OUTCOME MEASURES

Left ventricular output indexed to body weight and vital organ perfusion were measured at 24 hrs of age by the radiolabeled microsphere method. Lung mechanics, including lung wet/dry weight ratio, total lung water, static compliance and functional residual capacity were measured immediately following euthanasia.

RESULTS

Total pulmonary blood flow was significantly lower (p = .0001) in group 2 (mean = 94 mL/min/kg), compared with group 1 (mean = 287 mL/min/kg). Systemic blood flow and effective pulmonary blood flow were higher in group 1 (p = .07). No significant difference between groups in absolute organ blood flow was noted, although flow as a percent of left ventricular index was significantly higher in all organs except the kidney in group 2. There was no difference in arterial blood gas values, parameters of mechanical ventilation, percent lung water, or postmortem measurement of lung mechanics between groups.

CONCLUSION

Early ductal ligation did not result in improved cardiac output, increased organ blood flow, or improved pulmonary function. We postulate that gradual constriction of the ductus arteriosus may play an important role in successful cardiovascular adaptation in the premature infant. While it is clear that premature infants with symptomatic patent ductus arteriosus often benefit from ductal closure, we question the practice of prophylactic early ductal closure.

Pulmonary effects of closure of patent ductus arteriosus in premature infants with severe respiratory distress syndrome

The pulmonary effects of closure of a patent ductus arteriosus (PDA) were investigated in 11 premature infants with severe respiratory distress syndrome. Successful closure of a PDA did not improve the short-term severity of pulmonary disease (24 and 48 h after treatment) as judged by the arterial/alveolar oxygen tension ratio or the amount of ventilatory support. Also, pulmonary mechanics measured 24 h before, 24 and 48 h after treatment, were not statistically different.

CONCLUSION

Infants with severe respiratory disease requiring high ventilation pressure and high oxygen concentration, where structural changes in the lungs are already established, will rarely show short-term improvement in pulmonary disease as a result of closure of a PDA. The overall clinical condition may, however, improve as a result of reduced cardiovascular strain. Earlier treatment of a PDA could reduce the ventilation period and the possible risk of developing chronic lung disease.

Effects of patent ductus arteriosus on left ventricular output and organ blood flows in preterm infants with respiratory distress syndrome treated with surfactant

Thirty preterm infants (birth weight < 1500 gm) treated with Surfactant TA for the respiratory distress syndrome, who had no complicating clinical problems other than ductal patency, were studied by serial Doppler flow examinations to determine the effects of early left-to-right shunt through the patent ductus arteriosus on the left ventricular output and organ blood flows. Doppler flow variables in 15 infants with a hemodynamically significant patent ductus arteriosus (hsPDA) were compared with those in 15 subjects without hsPDA matched for age, body weight, and gestational age. Infants with hsPDA had significantly higher left ventricular output and significantly lower blood flow volume in the abdominal aorta, and lower temporal mean blood flow velocities, with concomitant increases in the relative vascular resistance in the celiac artery, superior mesenteric artery, and renal artery. Pulsatility indexes of these vessels and the anterior cerebral artery were significantly higher in the hsPDA group, but the temporal mean blood flow velocities in the anterior cerebral artery and its vascular resistance were not significantly different between the two groups. After closure of the patent ductus arterious was achieved with mefenamic acid therapy, alterations in Doppler flow variables in the hsPDA group reverted to the levels seen in the group without hsPDA. These results suggest that despite large left-to-right ductal shunting, the heart of the preterm infant is capable of mounting a compensatory increase of cardiac output sufficient to maintain unchanged cerebral blood flow, but is unable to maintain postductal organ blood flows because of decreased perfusion pressure (ductal steal) and localized increase in vascular resistance.