Milrinone enhances relaxation to prostacyclin and iloprost in pulmonary arteries isolated from lambs with persistent pulmonary hypertension of the newborn

Congenital Diaphragmatic Hernia: Pulmonary Hypertension and Pulmonary Vascular Disease

This review provides a comprehensive summary of the current understanding of pulmonary hypertension (PH) in congenital diaphragmatic hernia, outlining the underlying pathophysiologic mechanisms, methods for assessing PH severity, optimal management strategies, and prognostic implications.

Vascular reactivity is altered in the placentas of fetuses with congenital diaphragmatic hernia

INTRODUCTION

Infants with congenital diaphragmatic hernia (CDH) often develop pulmonary hypertension but frequently fail to respond to vasodilator therapy, for instance because of an altered pulmonary vasoreactivity. Investigating such alterations in vivo is impossible. We hypothesised that these alterations are also present in fetoplacental vessels, since both vasculatures are exposed to the same circulating factors (e.g. endothelin-1) and respond similarly to certain stimuli (e.g. hypoxia). As proof-of-concept, we compared fetoplacental vasoreactivity between healthy and CDH-affected placentas.

METHODS

Fetoplacental vascular function of healthy and antenatally diagnosed left-sided CDH fetuses was assessed by wire myography. Placental expression of enzymes and receptors involved in the altered vasoreactive pathways was measured using quantitative PCR.

RESULTS

CDH arteries (n = 6) constricted more strongly to thromboxane A2 agonist U46619 (p < 0.001) and dilated less to bradykinin (p = 0.01) and nitric oxide (NO)-donor sodium nitroprusside (p = 0.04) than healthy arteries (n = 8). Vasodilation to prostacyclin analogue iloprost and adenylate cyclase stimulator forskolin, and vasoconstriction to endothelin-1 were not different between both groups. Angiotensin II did not induce vasoconstriction. Phosphodiesterase inhibitors sildenafil and milrinone did not affect responses to sodium nitroprusside, forskolin, or U46619. The mRNA expression of guanylate cyclase 1 soluble subunit alpha 1 (p = 0.003) and protein kinase cyclic guanine monophosphate (cGMP)-dependent 1 (p = 0.02) were reduced in CDH versus healthy placentas.

DISCUSSION

The identified changes in the thromboxane and NO-cGMP pathways in the fetoplacental vasculature correspond with currently described alterations in the pulmonary vasculature in CDH. Therefore, fetoplacental arteries may provide an opportunity to predict pulmonary therapeutic responses in infants with CDH.

Evidence-Based Guidelines for Acute Stabilization and Management of Neonates with Persistent Pulmonary Hypertension of the Newborn

Persistent pulmonary hypertension of the newborn, or PPHN, represents a challenging condition associated with high morbidity and mortality. Management is complicated by complex pathophysiology and limited neonatal specific evidence-based literature, leading to a lack of universal contemporary clinical guidelines for the care of these patients. To address this need and to provide consistent high-quality clinical care for this challenging population in our neonatal intensive care unit, we sought to develop a comprehensive clinical guideline for the acute stabilization and management of neonates with PPHN. Utilizing cross-disciplinary expertise and incorporating an extensive literature search to guide best practice, we present an approachable, pragmatic, and clinically relevant guide for the bedside management of acute PPHN. KEY POINTS: · PPHN is associated with several unique diagnoses; the associated pathophysiology is different for each unique diagnosis.. · PPHN is a challenging, dynamic, and labile process for which optimal care requires frequent reassessment.. · Key management goals are adequate tissue oxygen delivery, avoiding harm..

Worsened short-term clinical outcomes in a cohort of patients with iNO-unresponsive PPHN: a case for improving iNO responsiveness

OBJECTIVES

To identify distinguishing characteristics of neonates with persistent pulmonary hypertension of the newborn (PPHN) unresponsive to inhaled nitric oxide (iNO) and evaluate the use of milrinone in this cohort.

STUDY DESIGN

Retrospective chart review of 99 neonates with PPHN treated with iNO over a five-year period at a quaternary neonatal intensive care unit.

RESULTS

Neonates with iNO-unresponsive PPHN had an increased number of ventilator days (10 vs 7 days, p = 0.02), greater length of hospital stay (30 vs 22 days, p = 0.02), and increased risk of death or ECMO than iNO-responsive neonates (p = 0.03). Inhaled NO non-responders treated with milrinone had improved oxygenation (p < 0.03) and no change in systemic hemodynamics.

CONCLUSION

Neonates with iNO-unresponsive PPHN had worse clinical outcomes than iNO responders. Milrinone may be a safe and effective adjuvant therapy, although large-scale studies are lacking. Identifying early predictors of iNO response and novel strategies to enhance iNO responsiveness should be prioritized.

Effects of Neonatal Caffeine Administration on Vessel Reactivity in Adult Mice

OBJECTIVE

The effects of neonatal caffeine therapy in adults born preterm are uncertain. We studied the impact of neonatal caffeine on systemic blood pressure, vessel reactivity, and response to stress in adult mice.

STUDY DESIGN

Mice pups were randomized to caffeine (20 mg/kg/d) or saline by intraperitoneal injection for 10 days after birth. We performed tail-cuff BP (8/12 weeks), urinary 8-hydroxydeoxyguanosine and fecal corticosterone (14 weeks), and vessel reactivity in aortic rings (16 weeks) in adult mice.

RESULTS

No differences were noted in systolic, diastolic, and mean blood pressures between the two groups at 8 and 12 weeks of age. However, norepinephrine-induced vasoconstriction was substantially higher in aortic rings in CAF-treated male mice. More significant vasodilator responses to nitric oxide donors in aortic rings in female mice may suggest gender-specific effects of caffeine. Female mice exposed to caffeine had significantly lower body weight over-time. Caffeine-treated male mice had substantially higher fecal corticosterone and urinary 8-hydroxydeoxyguanosine at 14 weeks, suggestive of chronic stress.

CONCLUSION

We conclude sex-specific vulnerability to the heightened vascular tone of the aorta in male mice following neonatal caffeine therapy. Altered vessel reactivity and chronic stress in the presence of other risk factors may predispose to the development of systemic hypertension in adults born preterm.

Life-threatening PPHN refractory to nitric oxide: proposal for a rational therapeutic algorithm

Persistent pulmonary hypertension of the neonate (PPHN) refractory to inhaled nitric oxide still represents a frequent clinical challenge with negative outcomes in neonatal critical care. Several pulmonary vasodilators have become available thanks to improved understanding of pulmonary hypertension pathobiology. These drugs are commonly used in adults and there are numerous case series and small studies describing their potential usefulness in neonates, as well. New vasodilators act on different pathways, some of them can have additive effects and all have different pharmacology features. This information has never been summarized so far and no comprehensive pathobiology-driven algorithm is available to guide the treatment of refractory PPHN.Conclusion: We offer a rational clinical algorithm to guide the treatment of refractory PPHN based on expert advice and the more recent pathobiology and pharmacology knowledge. What is Known: • Refractory PPHN occurs in 30-40% of iNO-treated neonates and represents a significant clinical problem. Several pulmonary vasodilators have become available thanks to a better understanding of pulmonary hypertension pathobiology. What is New: • Available vasodilators have different pharmacology, mechanisms of action and may provide additive effect. We provide a rational clinical algorithm to guide the treatment of refractory PPHN based on expert advice and the more recent pathobiology and pharmacology knowledge.

Pathophysiology and Management of Persistent Pulmonary Hypertension of the Newborn

Persistent pulmonary hypertension of the newborn (PPHN) is a disorder of circulatory transition resulting in high pulmonary vascular resistance with extrapulmonary right-to-left shunts causing hypoxemia. There has been substantial gain in understanding of pathophysiology of PPHN over the past 2 decades, and biochemical pathways responsible for abnormal vasoconstriction of pulmonary vasculature are now better understood. Easy availability of bedside echocardiography helps in establishing early definitive diagnosis, understanding the pathophysiology and hemodynamic abnormalities, monitoring the disease process, and response to therapeutic intervention. There also has been significant advancement in specific management of PPHN targeted at deranged biochemical pathways and hemodynamic instability.

The newborn sheep translational model for pulmonary arterial hypertension of the neonate at high altitude

Chronic hypoxia during gestation induces greater occurrence of perinatal complications such as intrauterine growth restriction, fetal hypoxia, newborn asphyxia, and respiratory distress, among others. This condition may also cause a failure in the transition of the fetal to neonatal circulation, inducing pulmonary arterial hypertension of the neonate (PAHN), a syndrome that involves pulmonary vascular dysfunction, increased vasoconstrictor tone and pathological remodeling. As this syndrome has a relatively low prevalence in lowlands (~7 per 1000 live births) and very little is known about its prevalence and clinical evolution in highlands (above 2500 meters), our understanding is very limited. Therefore, studies on appropriate animal models have been crucial to comprehend the mechanisms underlying this pathology. Considering the strengths and weaknesses of any animal model of human disease is fundamental to achieve an effective and meaningful translation to clinical practice. The sheep model has been used to study the normal and abnormal cardiovascular development of the fetus and the neonate for almost a century. The aim of this review is to highlight the advances in our knowledge on the programming of cardiopulmonary function with the use of high-altitude newborn sheep as a translational model of PAHN.

Management of systemic hypotension in term infants with persistent pulmonary hypertension of the newborn: an illustrated review

In persistent pulmonary hypertension of the newborn (PPHN), the ratio of pulmonary vascular resistance to systemic vascular resistance is increased. Extrapulmonary shunts (patent ductus arteriosus and patent foramen value) allow for right-to-left shunting and hypoxaemia. Systemic hypotension can occur in newborns with PPHN due to variety of reasons, such as enhanced peripheral vasodilation, impaired left ventricular function and decreased preload. Systemic hypotension can lead to end organ injury from poor perfusion and hypoxaemia in the newborn with PPHN. Thus, it must be managed swiftly. However, not all newborns with PPHN and systemic hypotension can be managed the same way. Individualised approach based on physiology and echocardiographic findings are necessary to improve perfusion to essential organs. Here we present a review of the physiology and mechanisms of systemic hypotension in PPHN, which can then guide treatment.

Nitric oxide activates AMPK by modulating PDE3A in human pulmonary artery smooth muscle cells

Phosphodiesterase 3 (PDE3), of which there are two isoforms, PDE3A and PDE3B, hydrolyzes cAMP and cGMP—cyclic nucleotides important in the regulation of pulmonary vascular tone. PDE3 has been implicated in pulmonary hypertension unresponsive to nitric oxide (NO); however, contributions of the two isoforms are not known. Furthermore, adenosine monophosphate‐activated protein kinase (AMPK), a critical regulator of cellular energy homeostasis, has been shown to be modulated by PDE3 in varying cell types. While AMPK has recently been implicated in pulmonary hypertension pathogenesis, its role and regulation in the pulmonary vasculature remain to be elucidated. Therefore, we utilized human pulmonary artery smooth muscle cells (hPASMC) to test the hypothesis that NO increases PDE3 expression in an isoform‐specific manner, thereby activating AMPK and inhibiting hPASMC proliferation. We found that in hPASMC, NO treatment increased PDE3A protein expression and PDE3 activity with a concomitant decrease in cAMP concentrations and increase in AMPK phosphorylation. Knockdown of PDE3A using siRNA transfection blunted the NO‐induced AMPK activation, indicating that PDE3A plays an important role in AMPK regulation in hPASMC. Treatment with a soluble guanylate cyclase (sGC) stimulator increased PDE3A expression and AMPK activation similar to that seen with NO treatment, whereas treatment with a sGC inhibitor blunted the NO‐induced increase in PDE3A and AMPK activation. These results suggest that NO increases PDE3A expression, decreases cAMP, and activates AMPK via the sGC‐cGMP pathway. We speculate that NO‐induced increases in PDE3A and AMPK may have implications in the pathogenesis and the response to therapies in pulmonary hypertensive disorders.

Persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is a significant clinical problem characterized by refractory and severe hypoxemia secondary to elevated pulmonary vascular resistance resulting in right-to-left extrapulmonary shunting of deoxygenated blood. PPHN is associated with diverse cardiopulmonary disorders and a high early mortality rate for infants with severe PPHN. Surviving infants with PPHN have an increased risk of long-term morbidities. PPHN physiology can be categorized by (1) maladaptation: pulmonary vessels have normal structure and number but have abnormal vasoreactivity; (2) excessive muscularization: increased smooth muscle cell thickness and increased distal extension of muscle to vessels that are usually not muscularized; and (3) underdevelopment: lung hypoplasia associated with decreased pulmonary artery number. Treatment involves adequate lung recruitment, optimization of cardiac output and left ventricular function, and pulmonary vasodilators such as inhaled nitric oxide. Infants who fail to respond to conventional therapy should be evaluated for lethal lung disorders including alveolar-capillary dysplasia, T-box transcription factor 4 gene, thyroid transcription factor-1, ATP-binding cassette A3 gene, and surfactant protein diseases.

Milrinone Use in Persistent Pulmonary Hypertension of the Newborn

Failure of the normal transition from in utero to ex utero physiology leads to "persistent" pulmonary hypertension of the newborn (PPHN). PPHN is frequently associated with low systemic blood pressure and low cardiac output because of increased right ventricular afterload and myocardial dysfunction. The general management of newborns with PPHN is geared toward maintenance of normothermia, normal serum electrolytes, normal intravascular volume, correction of acidosis, adequate sedation/analgesia, adequate ventilation and oxygenation with optimal lung recruitment, and avoidance of hyperoxia. Inotropic and vasoactive agents are commonly initiated early to increase cardiac output, maintain adequate systemic blood pressure, and enhance oxygen delivery to the tissue. Unfortunately, there is not much evidence on the choice, timing of initiation, dosing, monitoring, and titrating of vasoactive agents in this patient population. In this review, we will discuss the pathophysiology of PPHN and review the use of inotropic, lusitropic, and vasoactive agents in the management of PPHN, with particular attention to milrinone.

The Natural-Mineral-Based Novel Nanomaterial IFMC Increases Intravascular Nitric Oxide without Its Intake: Implications for COVID-19 and beyond

There are currently no promising therapy strategies for either the treatment or prevention of novel coronavirus disease 2019 (COVID-19), despite the urgent need. In addition to respiratory diseases, vascular complications are rapidly emerging as a key threat of COVID-19. Existing nitric oxide (NO) therapies have been shown to improve the vascular system; however, they have different limitations in terms of safety, usability and availability. In light of this, we hypothesise that a natural-mineral-based novel nanomaterial, which was developed based on NO therapy, might be a viable strategy for the treatment and prevention of COVID-19. The present study examined if it could induce an increase of intravascular NO, vasodilation and the consequent increase of blood flow rate and temperature in a living body. The intravascular NO concentration in the hepatic portal of rats was increased by 0.17 nM over 35.2 s on average after its application. An ultrasonic Doppler flow meter showed significant increases in the blood flow rate and vessel diameter, but no difference in the blood flow velocity. These were corroborated by measurements of human hand surface temperature. To our knowledge, this result is the first evidence where an increase of intravascular NO and vasodilation were induced by bringing a natural-mineral-based nanomaterial into contact with or close to a living body. The precise mechanisms remain a matter for further investigation; however, we may assume that endothelial NO synthase, haemoglobin and endothelium-derived hyperpolarising factor are deeply involved in the increase of intravascular NO.

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

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

An update on the diagnosis and management of bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension

The past decade of neonatal care has been highlighted by increased survival rates in smaller and more premature infants. Despite reduction in mortality associated with extreme prematurity, long term pulmonary morbidities remain a concern, with growing recognition of the clinical burden attributable to infants with bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH). Recent publications shed light on the critical contributions of maternal placental pathology and compromised intrauterine growth to fetal pulmonary vascular development. A body of literature has further clarified postnatal risk factors for PH, most notably the severity of BPD but surprisingly the additional presence of non-pulmonary morbidities including necrotizing enterocolitis (NEC). Limitations of current diagnostics persist with growing consideration of novel echocardiographic approaches as well as complementary non-invasive biomarkers to better identify infants at risk. In 2015, a joint report published by the American Heart Association and American Thoracic Society provided the first guidelines for the care of children with PH with limited content to address BPD-associated PH. These guidelines were expanded upon in an expert consensus report produced by the Pediatric Pulmonary Hypertension Network (PPHNet). These recommendations encouraged the use of standardized screening protocols and emphasized the importance of evaluation and treatment of comorbidities when PH is identified. Cardiac catheterization was recommended prior to initiation of therapy for more accurate quantification of pulmonary pressures, clarification of anatomy and guidance in the use of pharmacotherapy. Despite these guidelines, significant practice variation persists and gaps remain with respect to optimal evaluation and management of BPD-associated PH.

Phosphodiesterase inhibitors: Potential role in the respiratory distress of neonates

Phosphodiesterases (PDEs) are a superfamily of enzymes that catalyze the hydrolysis of phosphodiester bonds of 3',5' cyclic adenosine and guanosine monophosphate (cAMP and cGMP). PDEs control hydrolysis of cyclic nucleotides in many cells and tissues. Inhibition of PDEs by selective or nonselective PDE inhibitors represents an effective targeted strategy for the treatment of various diseases including respiratory disorders. Recent data have demonstrated that PDE inhibitors can also be of benefit in respiratory distress in neonates. This article outlines the pharmacological properties of nonselective and selective PDE inhibitors and provides up-to-date information regarding their use in experimental models of neonatal respiratory distress as well as in clinical studies.

Intravenous epoprostenol improves oxygenation index in patients with persistent pulmonary hypertension of the newborn refractory to nitric oxide

OBJECTIVES

Evaluate the short-term effects of IV epoprostenol in neonates with persistent pulmonary hypertension (PPHN) of the newborn.

STUDY DESIGN

We reviewed 36 patients with inhaled nitric oxide (iNO) refractory PPHN placed on IV epoprostenol from 2010 to 2015. Patients were categorized as responders or non-responders (who either died or required extracorporeal membranous oxygenation).

RESULTS

There were 15 responders and 21 non-responders. Pulmonary hypoplasia was the etiology of PPHN for 57% of non-responders vs. 13% of responders. Median oxygenation index (OI) was similar at baseline (41.8 non-responders vs. 36.5 responders, p = 0.41) with responders having a significantly lower OI by 4 h of treatment (42.3 vs. 23.1, p = 0.002). Epoprostenol responders had a median OI decrease of 11.6 within 4 h (p = 0.017) with a significant response persisting through 24 h.

CONCLUSION

In infants with iNO-refractory PPHN, initiation of IV epoprostenol was associated with a significant and rapid OI reduction among responders.

Current and Future Treatments for Persistent Pulmonary Hypertension in the Newborn

Persistent pulmonary hypertension in newborn (PPHN) is a serious and possibly fatal syndrome characterized by sustained foetal elevation of pulmonary vascular resistance at birth. PPHN may manifest secondary to other conditions as meconium aspiration syndrome, infection and congenital diaphragmatic hernia. This MiniReview provides the reader with an overview of current and future treatment options for patients with PPHN without congenital diaphragmatic hernia. The study is based on systematic searches in the databases PubMed and Cochrane Library and registered studies on Clinicaltrials.gov investigating PPHN. Inhaled nitric oxide (iNO) is well documented for treatment of PPHN, but 30% fail to respond to iNO. Other current treatment options could be sildenafil, milrinone, prostaglandin analogues and bosentan. There are several ongoing trials with sildenafil, but evidence is lacking for the other treatments and/or for the combination with iNO. Currently, there is no evidence for effect in PPHN of other treatments, for example tadalafil, macitentan, ambrisentan, riociguat and selexipag used for pulmonary arterial hypertension in adults. Experimental studies in animal models for PPHN suggest effect of a series of approaches including recombinant human superoxide dismutase, L-citrulline, Rho-kinase inhibitors and peroxisome proliferator-activated receptor-γ agonists. We conclude that iNO is the most investigated and the only approved pulmonary vasodilator for infants with PPHN. In the iNO non-responders, sildenafil currently seems to be the best alternative either alone or in combination with iNO. Systematic and larger clinical studies are required for testing the other potential treatments of PPHN.

Response to pulmonary vasodilators in infants with congenital diaphragmatic hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) is associated with lung hypoplasia, cardiac dysfunction and pulmonary hypertension. Inhaled nitric oxide (iNO) and milrinone are commonly used pulmonary vasodilators in CDH. We studied the hemodynamic effects of iNO and milrinone in infants with CDH.

METHODS

A retrospective chart review was performed of all CDH infants admitted to two regional perinatal centers and infants classified into three groups: No-iNO group; iNO-responders and iNO-nonresponders. Oxygenation and hemodynamic effects of iNO and milrinone were assessed by blood gases and echocardiography.

RESULTS

Fifty-four percent (39/72) of infants with CDH received iNO and 31% of these infants (12/39) had complete oxygenation response to iNO. Oxygenation response to iNO was not associated with a decrease in right ventricular pressures (RVP) or ECMO use. Four infants (33%) in the iNO-responder group and eight infants (30%) in the iNO-nonresponder group received milrinone. Milrinone lowered RVP and improved ejection fraction (EF). Response to iNO was associated with improved oxygenation to milrinone and increased survival following ECMO (67 vs. 20% among nonresponders).

CONCLUSIONS

Response to inhaled nitric oxide in combination with milrinone may be associated with improved oxygenation and better survival after ECMO in infants with CDH.

Surgery for partial atrioventricular septal defect with pulmonary hypertension in an adult dog

A 4-year-old, 5.9-kg female Japanese Spitz presented with syncope and exercise intolerance. Echocardiography revealed an ostium primum atrial septal defect (ASD), a cleft mitral valve, mitral valve regurgitation (MR), and tricuspid regurgitation (TR) (velocity: 3.6 m/sec, pressure gradient: 52 mmHg), leading to a diagnosis of partial atrioventricular septal defect (AVSD) with moderate pulmonary hypertension (PH). Open-heart surgery using cardiopulmonary bypass was performed through right atriotomy. The cleft of the mitral valve was sutured with polypropylene and the AVSD was closed using an autologous pericardial patch fixed with glutaraldehyde. No postoperative pulmonary hypertensive crisis occurred. Shunting flow through the ASD, TR and PH had completely disappeared 2 months postoperatively; however, moderate MR persisted. The dog is still alive 5 years postoperatively without clinical signs.

Milrinone in congenital diaphragmatic hernia - a randomized pilot trial: study protocol, review of literature and survey of current practices

Background

Congenital diaphragmatic hernia (CDH) is commonly associated with pulmonary hypoplasia and pulmonary hypertension (PH). PH associated with CDH (CDH-PH) is frequently resistant to conventional pulmonary vasodilator therapy including inhaled nitric oxide (iNO) possibly due to right and left ventricular dysfunction. Milrinone is an intravenous inotrope and lusitrope with pulmonary vasodilator properties and has been shown anecdotally to improve oxygenation in PH. We developed this pilot study to determine if milrinone infusion would improve oxygenation in neonates ≥36 weeks postmenstrual age (PMA) with CDH.

Methods/design

Data on pulmonary vasodilator management and outcome of CDH patients was collected from 18 university NICUs affiliated with the Neonatal Research Network (NRN) from 2011 to 2012. The proposed pilot will be a masked, placebo–controlled, multicenter, randomized trial of 66 infants with CDH with an oxygenation index (OI) ≥10 or oxygen saturation index (OSI) ≥5. The primary outcome is the oxygenation response, as determined by change in OI at 24 h after initiation of study drug. As secondary outcomes, we will determine oxygenation at 48 h and 72 h post-infusion, right ventricular pressures on echocardiogram and the incidence of systemic hypotension, arrhythmias, intracranial hemorrhage, survival without extracorporeal membrane oxygenation, and chronic lung disease (oxygen need at 28 days postnatal age). Finally, we will evaluate the pulmonary and nutritional status at 4, 8 and 12 months of age using a phone questionnaire.

Results

Three hundred thirty-seven infants with CDH were admitted to NRN NICUs in 2011 and 2012 of which 275 were ≥36 weeks PMA and were exposed to the following pulmonary vasodilators: iNO (39%), sildenafil (17%), milrinone (17%), inhaled epoprostenol (6%), intravenous epoprostenol (3%), and intravenous PGE1 (1%). ECMO was required in 36% of patients. Survival to discharge was 71%.

Discussion

CDH is an orphan disease with high mortality with few randomized trials evaluating postnatal management. Intravenous milrinone is a commonly used medication in neonatal/pediatric intensive care units and is currently used in 17% of patients with CDH within the NRN. This pilot study will provide data and enable further studies evaluating pulmonary vasodilator therapy in CDH.

Trial registration

ClinicalTrials.gov; NCT02951130; registered 14 October 2016.

Persistent pulmonary hypertension of the newborn

Failure of the normal circulatory adaptation to extrauterine life results in persistent pulmonary hypertension of the newborn (PPHN). Although this condition is most often secondary to parenchymal lung disease or lung hypoplasia, it may also be idiopathic. PPHN is characterized by elevated pulmonary vascular resistance with resultant right-to-left shunting of blood and hypoxemia. Although the preliminary diagnosis of PPHN is often based on differential cyanosis and labile hypoxemia, the diagnosis is confirmed by echocardiography. Management strategies include optimal lung recruitment and use of surfactant in patients with parenchymal lung disease, maintaining optimal oxygenation and stable blood pressures, avoidance of respiratory and metabolic acidosis and alkalosis, and pulmonary vasodilator therapy. Extracorporeal membrane oxygenation is considered when medical management fails. Although mortality associated with PPHN has decreased significantly with improvements in medical care, there remains the potential risk for neurodevelopmental disability which warrants close follow-up of affected infants after discharge.

Effect of Milrinone Infusion on Pulmonary Vasculature and Stroke Work Indices: A Single-Center Retrospective Analysis in 69 Patients Awaiting Cardiac Transplantation

BACKGROUND

Although milrinone infusion is reported to benefit left ventricular function in chronic left heart failure, few insights exist regarding its effects on pulmonary circulation and right ventricular function.

METHODS

We retrospectively reviewed right heart catheterization data at baseline and during continuous infusion of milrinone in 69 patients with advanced heart failure and analyzed the effects on ventricular stroke work indices, pulmonary vascular resistance and pulmonary arterial compliance.

RESULTS

Compared to baseline, milrinone infusion after a mean 58 ± 61 days improved mean left ventricular stroke work index (1540 ± 656 vs. 2079 ± 919 mmHg·mL/m², p = 0.0007) to a much greater extent than right ventricular stroke work index (616 ± 346 vs. 654 ± 332, p = 0.053); however, patients with below median stroke work indices experienced a significant improvement in both left and right ventricular stroke work performance. Overall, milrinone reduced left and right ventricular filling pressures and pulmonary and systemic vascular resistance by approximately 20%. Despite an increase in pulmonary artery capacitance (2.3 ± 1.6 to 3.0 ± 2.0, p = 0.013) and a reduction in pulmonary vascular resistance (3.8 ± 2.3 to 3.0 ± 1.7 Wood units), milrinone did not reduce the transpulmonary gradient (13 ± 7 vs. 12 ± 6 mmHg, p = 0.252), the pulmonary artery pulse pressure (25 ± 10 vs. 24 ± 10, p = 0.64) or the pulmonary artery diastolic to pulmonary capillary wedge gradient (2.0 ± 6.5 vs. 2.4 ± 6.0, p = 0.353).

CONCLUSION

Milrinone improved left ventricular stroke work indices to a greater extent than right ventricular stroke work indices and had beneficial effects on right ventricular net input impedance, predominantly via augmentation of left ventricular stroke volume and passive unloading of the pulmonary circuit. Patients who had the worst biventricular performance benefited the most from chronic milrinone infusion.

Congenital Diaphragmatic hernia - a review

Congenital Diaphragmatic hernia (CDH) is a condition characterized by a defect in the diaphragm leading to protrusion of abdominal contents into the thoracic cavity interfering with normal development of the lungs. The defect may range from a small aperture in the posterior muscle rim to complete absence of diaphragm.

The pathophysiology of CDH is a combination of lung hypoplasia and immaturity associated with persistent pulmonary hypertension of newborn (PPHN) and cardiac dysfunction. Prenatal assessment of lung to head ratio (LHR) and position of the liver by ultrasound are used to diagnose and predict outcomes. Delivery of infants with CDH is recommended close to term gestation. Immediate management at birth includes bowel decompression, avoidance of mask ventilation and endotracheal tube placement if required. The main focus of management includes gentle ventilation, hemodynamic monitoring and treatment of pulmonary hypertension followed by surgery. Although inhaled nitric oxide is not approved by FDA for the treatment of PPHN induced by CDH, it is commonly used.

Extracorporeal membrane oxygenation (ECMO) is typically considered after failure of conventional medical management for infants ≥ 34 weeks’ gestation or with weight >2 kg with CDH and no associated major lethal anomalies. Multiple factors such as prematurity, associated abnormalities, severity of PPHN, type of repair and need for ECMO can affect the survival of an infant with CDH. With advances in the management of CDH, the overall survival has improved and has been reported to be 70-90% in non-ECMO infants and up to 50% in infants who undergo ECMO.

Pharmacologic strategies in neonatal pulmonary hypertension other than nitric oxide

Inhaled nitric oxide (iNO) is approved for use in persistent pulmonary hypertension of the newborn (PPHN) but does not lead to sustained improvement in oxygenation in one-third of patients with PPHN. Inhaled NO is less effective in the management of PPHN secondary to congenital diaphragmatic hernia (CDH), extreme prematurity, and bronchopulmonary dysplasia (BPD). Intravenous pulmonary vasodilators such as prostacyclin, alprostadil, sildenafil, and milrinone have been successfully used in PPHN resistant to iNO. Oral pulmonary vasodilators such as endothelin receptor antagonist bosentan and phosphodiesterase-5 inhibitors such as sildenafil and tadalafil are used both during acute and chronic phases of PPHN. In the absence of infection, glucocorticoids may also be effective in PPHN. Many of these pharmacologic agents are not approved for use in PPHN and our knowledge is based on case reports and small trials. Large multicenter randomized controlled trials with long-term follow-up are required to evaluate alternate pharmacologic strategies in PPHN.

Advances in Neonatal Pulmonary Hypertension

Persistent pulmonary hypertension of the newborn (PPHN) is a surprisingly common event in the neonatal intensive care unit, and affects both term and preterm infants. Recent studies have begun to elucidate the maternal, fetal and genetic risk factors that trigger PPHN. There have been numerous therapeutic advances over the last decade. It is now appreciated that oxygen supplementation, particularly for the goal of pulmonary vasodilation, needs to be approached as a therapy that has risks and benefits. Administration of surfactant or inhaled nitric oxide (iNO) therapy at a lower acuity of illness can decrease the risk of extracorporeal membrane oxygenation/death, progression of disease and duration of hospital stay. Milrinone may have specific benefits as an 'inodilator', as prolonged exposure to iNO plus oxygen may activate phosphodiesterase (PDE) 3A. Additionally, sildenafil and hydrocortisone may benefit infants exposed to hyperoxia and oxidative stress. Continued investigation is likely to reveal new therapies such as citrulline and cinaciguat that will enhance NO synthase and soluble guanylate cyclase function. Continued laboratory and clinical investigation will be needed to optimize treatment and improve outcomes.

Persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by elevated pulmonary vascular resistance resulting in right-to-left shunting of blood and hypoxemia. PPHN is often secondary to parenchymal lung disease (such as meconium aspiration syndrome, pneumonia or respiratory distress syndrome) or lung hypoplasia (with congenital diaphragmatic hernia or oligohydramnios) but can also be idiopathic. The diagnosis of PPHN is based on clinical evidence of labile hypoxemia often associated with differential cyanosis. The diagnosis is confirmed by the echocardiographic demonstration of - (a) right-to-left or bidirectional shunt at the ductus or foramen ovale and/or, (b) flattening or leftward deviation of the interventricular septum and/or, (c) tricuspid regurgitation, and finally (d) absence of structural heart disease. Management strategies include optimal oxygenation, avoiding respiratory and metabolic acidosis, blood pressure stabilization, sedation and pulmonary vasodilator therapy. Failure of these measures would lead to consideration of extracorporeal membrane oxygenation (ECMO); however decreased need for this rescue therapy has been documented with advances in medical management. While trends also note improved survival, long-term neurodevelopmental disabilities such as deafness and learning disabilities remain a concern in many infants with severe PPHN. Funded by: 1R01HD072929-0 (SL).

Treatment of premature infants with pulmonary hypertension and right ventricular dysfunction with milrinone: a case series

OBJECTIVE

Milrinone has been proposed as an effective treatment for pulmonary hypertension (PH) and right ventricular (RV) dysfunction. We aimed to determine the effect of milrinone therapy on clinical and echocardiography parameters of PH in preterm infants with elevated pulmonary pressures.

STUDY DESIGN

A retrospective case review was conducted on infants <32 weeks gestation who received milrinone for the treatment of PH and reduced RV function. Echocardiographic data were collected before and after treatment with milrinone, and serial clinical parameters were recorded over a 72h  period.

RESULT

Seven infants met the inclusion criteria with a median gestation and birth weight of 27.3 weeks and 1140 g, respectively. Four infants had a diagnosis of pulmonary hypoplasia with PH, and three infants were recipients in twin-to-twin transfusion syndrome who also developed PH. Nitric oxide was used in six infants before commencement of milrinone. Milrinone was commenced at a dose of 0.33 μg kg(-1) min(-1) to 0.5 μg kg(-1) min(-1) and continued for a median duration of 70 h. Use of milrinone was associated with a fall in oxygenation index and inhaled nitric oxide dose. Following an initial fall in blood pressure over the first 6 h, there was an increase in blood pressure over the subsequent 72 h. Echocardiographic data demonstrated an increase in indicators of myocardial performance and PH. One infant died before discharge.

CONCLUSION

This case series suggests that milrinone may be a useful therapy for premature infants with echocardiography findings of PH and/or RH dysfunction. This data support the need for a randomised control trial to confirm its efficacy.

Altered prostanoid metabolism contributes to impaired angiogenesis in persistent pulmonary hypertension in a fetal lamb model

BACKGROUND

Persistent pulmonary hypertension of the newborn (PPHN) is associated with decreased lung angiogenesis and impaired pulmonary vasodilatation at birth. Prostanoids are important modulators of vascular tone and angiogenesis. We hypothesized that altered levels of prostacyclin (PGI₂), a potent vasodilator, and thromboxane A₂ (TXA₂), a vasoconstrictor, contribute to impaired angiogenesis of pulmonary artery endothelial cells (PAEC) in PPHN.

METHODS

PAEC were isolated from fetal lambs with PPHN induced by prenatal ductus arteriosus constriction or from sham operated controls. Expression and activity of PGI₂ synthase (PGIS) and TXA₂ synthase (TXAS), expression of cyclooxygenases 1 and 2 (COX-1 and COX-2), and the role of PGIS/TXAS alterations in angiogenesis were investigated in PAEC from PPHN and control lambs.

RESULTS

PGIS protein and activity were decreased and PGIS protein tyrosine nitration was increased in PPHN PAEC. In contrast, TXAS protein and its stimulated activity were increased in PPHN PAEC. COX-1 and COX-2 proteins were decreased in PPHN PAEC. Addition of PGI₂ improved in vitro tube formation by PPHN PAEC, whereas indomethacin decreased tube formation by control PAEC. PGIS knockdown decreased the in vitro angiogenesis in control PAEC, whereas TXAS knockdown increased the in vitro angiogenesis in PPHN PAEC.

CONCLUSION

Reciprocal alterations in PGI₂ and TXA₂ may contribute to impaired angiogenesis in PPHN.

Pulmonary hypertension management in neonates

The management of pulmonary hypertension is multi-faceted, with therapies directed at supporting cardiovascular and pulmonary function, treating the underlying cause (if feasible), and preventing irreversible remodeling of the pulmonary vasculature. Recently, manipulation of signaling pathways and mediators contained within the pulmonary vascular endothelial cell has become a new target. This article will review the pathophysiology of pulmonary hypertension and the broad principles involved in its management, with specific emphasis on pharmacological therapies directed at the pulmonary vascular endothelium.

A comprehensive study of clinical biomarkers, use of inotropic medications and fluid resuscitation in newborns with persistent pulmonary hypertension

Persistent pulmonary hypertension of the newborn (PPHN) is associated with high morbidity and mortality. This study evaluated clinical outcomes in PPHN in relation to echocardiographic (EC) markers, score of neonatal acute physiology, perinatal extension, version II (SNAPPE II) scores, inotropic agent use, and the amount of fluid received as boluses. In this retrospective chart analysis of 98 neonates with PPHN born at >34 weeks' gestation, we compared two cohorts of newborns: those who received inhaled nitric oxide and mechanical ventilation only, and who survived to discharge (Group 1); and those who required extracorporeal membrane oxygenation (ECMO) or who died (Group 2). Of 21 EC parameters assessed, seven were significantly different between Group 1 and Group 2. Eleven (24.4%) newborns in Group 2 had decreased left ventricular (LV) function, compared with three (5.1%) in Group 1 (p = 0.011). Median SNAPPE II scores were significantly higher in Group 2 than in Group 1 (p < 0.001). Newborns in Group 2 also received a significantly higher amount of fluid as boluses during the first 7 days of hospitalization compared with Group 1 (p = 0.018). Following logistic regression analysis, only the difference in total SNAPPE II score retained statistical significance (p < 0.001); however, the total amount of fluid administered as boluses trended higher (p = 0.087) for newborns in Group 2. Our findings show that SNAPPE II scores may help guide counseling for parents of newborns with PPHN regarding the likelihood of death or the need for ECMO. Limiting fluid boluses may improve outcomes in newborns with high SNAPPE II scores and decreased LV function.

Oral sildenafil and inhaled iloprost in the treatment of pulmonary hypertension of the newborn

OBJECTIVE

This study was performed to examine the effectiveness and safety of oral sildenafil and inhaled iloprost in term newborns with persistent pulmonary hypertension of the newborn (PPHN).

PATIENTS AND METHODS

Oral sildenafil and inhaled iloprost were administered to 27 and 20 neonates, respectively, for treatment of persistent pulmonary hypertension. All patients were term infants at 37 gestational weeks or older. In the sildenafil group, 14 patients had meconium aspiration syndrome, 8 had asphyxia (hypoxic ischemic encephalopathy stages II and III), 3 had congenital pneumonia, 1 had transient tachypnea, and 1 had idiopathic PPHN. In the iloprost group, 9 patients had meconium aspiration syndrome, 7 had asphyxia (hypoxic ischemic encephalopathy stages II and III), 3 had congenital pneumonia, and 1 had transient tachypnea. Sildenafil citrate was administered via an oral feeding tube. Iloprost was administered endotracheally to patients on mechanical ventilation using a jet nebulizer.

RESULTS

Iloprost appeared to be more effective than sildenafil in the treatment of PPHN with regard to time to adequate clinical response, ventilatory parameters, duration of drug administration, duration of mechanical ventilation, duration of return to normal values of respiratory failure indices, use of MgSO4 as a second vasodilator and requirement for support with inotropic agents. We observed no side effects on blood pressure or homeostasis in any of the patients in the iloprost group. Systemic hypotension was significantly elevated in the sildenafil group. Four and three infants died of PPHN in the sildenafil and iloprost groups, respectively. Pulmonary systolic arterial pressure decreased to normal levels in the remaining 40 patients, and they were discharged from hospital.

CONCLUSION

We suggested that inhaled iloprost may be a safe and effective treatment choice in newborn infants with persistent pulmonary hypertension. In cases where treatment with inhaled iloprost, ECMO or INO is not possible, oral sildenafil can be an alternative therapy option in the treatment of PPHN.

Prenatal programming of pulmonary hypertension induced by chronic hypoxia or ductal ligation in sheep

Pulmonary hypertension of the newborn is caused by a spectrum of functional and structural abnormalities of the cardiopulmonary circuit. The existence of multiple etiologies and an incomplete understanding of the mechanisms of disease progression have hindered the development of effective therapies. Animal models offer a means of gaining a better understanding of the fundamental basis of the disease. To that effect, a number of experimental animal models are being used to generate pulmonary hypertension in the fetus and newborn. In this review, we compare the mechanisms associated with pulmonary hypertension caused by two such models: in utero ligation of the ductus arteriosus and chronic perinatal hypoxia in sheep fetuses and newborns. In this manner, we make direct comparisons between ductal ligation and chronic hypoxia with respect to the associated mechanisms of disease, since multiple studies have been performed with both models in a single species. We present evidence that the mechanisms associated with pulmonary hypertension are dependent on the type of stress to which the fetus is subjected. Such an analysis allows for a more thorough evaluation of the disease etiology, which can help focus clinical treatments. The final part of the review provides a clinical appraisal of current treatment strategies and lays the foundation for developing individualized therapies that depend on the causative factors.

Update on PPHN: mechanisms and treatment

Persistent pulmonary hypertension of the newborn (PPHN) is a syndrome of failed circulatory adaptation at birth, seen in about 2/1000 live born infants. While it is mostly seen in term and near-term infants, it can be recognized in some premature infants with respiratory distress or bronchopulmonary dysplasia. Most commonly, PPHN is secondary to delayed or impaired relaxation of the pulmonary vasculature associated with diverse neonatal pulmonary pathologies, such as meconium aspiration syndrome, congenital diaphragmatic hernia, and respiratory distress syndrome. Gentle ventilation strategies, lung recruitment, inhaled nitric oxide, and surfactant therapy have improved outcome and reduced the need for extracorporeal membrane oxygenation (ECMO) in PPHN. Newer modalities of treatment discussed in this article include systemic and inhaled vasodilators like sildenafil, prostaglandin E1, prostacyclin, and endothelin antagonists. With prompt recognition/treatment and early referral to ECMO centers, the mortality rate for PPHN has significantly decreased. However, the risk of potential neurodevelopmental impairment warrants close follow-up after discharge for infants with PPHN.

Milrinone relaxes pulmonary veins in guinea pigs and humans

Introduction

The phosphodiesterase-III inhibitor milrinone improves ventricular contractility, relaxes pulmonary arteries and reduces right ventricular afterload. Thus, it is used to treat heart failure and pulmonary hypertension (PH). However, its action on pulmonary veins (PVs) is not defined, although particularly PH due to left heart disease primarily affects the pulmonary venous bed. We examined milrinone-induced relaxation in PVs from guinea pigs (GPs) and humans.

Material and Methods

Precision-cut lung slices (PCLS) were prepared from GPs or from patients undergoing lobectomy. Milrinone-induced relaxation was studied by videomicroscopy in naïve PVs and in PVs pre-constricted with the ET_A-receptor agonist BP0104. Baseline luminal area was defined as 100%. Intracellular cAMP was measured by ELISA and milrinone-induced changes of segmental vascular resistances were studied in the GP isolated perfused lung (IPL).

Results

In the IPL (GP), milrinone (10 µM) lowered the postcapillary resistance of pre-constricted vessels. In PCLS (GP), milrinone relaxed naïve and pre-constricted PVs (120%) and this relaxation was attenuated by inhibition of protein kinase G (KT 5823), adenyl cyclase (SQ 22536) and protein kinase A (KT 5720), but not by inhibition of NO-synthesis (L-NAME). In addition, milrinone-induced relaxation was dependent on the activation of K_ATP-, BK_Ca²⁺- and K_v-channels. Human PVs also relaxed to milrinone (121%), however only if pre-constricted.

Discussion

Milrinone relaxes PVs from GPs and humans. In GPs, milrinone-induced relaxation is based on K_ATP-, BK_Ca²⁺- and K_v-channel-activation and on cAMP/PKA/PKG. The relaxant properties of milrinone on PVs lead to reduced postcapillary resistance and hydrostatic pressures. Hence they alleviate pulmonary edema and suggest beneficial effects of milrinone in PH due to left heart disease.

Diagnosis and treatment of pulmonary hypertension in infancy

Normal pulmonary vascular development in infancy requires maintenance of low pulmonary vascular resistance after birth, and is necessary for normal lung function and growth. The developing lung is subject to multiple genetic, pathological and/or environmental influences that can adversely affect lung adaptation, development, and growth, leading to pulmonary hypertension. New classifications of pulmonary hypertension are beginning to account for these diverse phenotypes, and or pulmonary hypertension in infants due to PPHN, congenital diaphragmatic hernia, and bronchopulmonary dysplasia (BPD). The most effective pharmacotherapeutic strategies for infants with PPHN are directed at selective reduction of PVR, and take advantage of a rapidly advancing understanding of the altered signaling pathways in the remodeled vasculature.

Role of pulmonary artery reactivity and nitric oxide in injury and inflammation following lung contusion

The mechanisms contributing to hypoxia in lung contusion (LC) remain unclear and not temporally associated with the peak onset of acute inflammation. We investigated the role of oxidative stress in alteration of pulmonary arterial (PA) reactivity following LC. In addition, the role of antioxidants in reversing this process was examined. PaO2 and PA reactivity were measured in rats subjected to bilateral LC. Rings were pretreated with a nitric oxide synthase (NOS) inhibitor, L-nitro arginine (10(-3) M), or PEG-superoxide dismutase (SOD) and PEG-catalase (CAT), or both (L-nitro arginine + SOD/CAT). Rings were constricted with norepinephrine and relaxed with an NOS agonist (A23187) or NO donor (SNAP [S-nitrosyl amino penicillamine]). Immunochemical and mass spectrometric quantification for nitrotyrosine was performed. Rats were hypoxemic at 4 h after contusion compared with controls, but recovered by 24 h (PaO(2)/FIO(2) ratio: baseline, 443 ± 28; 4 h, 288 ± 46; and 24 h, 417 ± 23). Pulmonary arterial constriction to NOS inhibition and relaxation to A23187 were impaired 4 h after LC. Pulmonary arterial relaxation to SNAP was decreased at 4 and 24 h after LC. These alterations in PA reactivity were reversed by SOD/CAT pretreatment. SOD1 and 2 mRNA were upregulated, and soluble guanylyl cyclase mRNA was downregulated 24 h after LC. Immunohistochemistry and mass spectrometry revealed that levels of 3-nitrotyrosine were increased markedly at 4 h following LC consistent with superoxide generation and formation of peroxynitrite. Collectively, these data suggest that consumption of NO due to excess superoxide resulting in peroxynitrite formation leads to diminished vascular reactivity following LC.

Persistent pulmonary hypertension of the newborn: recent advances in pathophysiology and treatment

OBJECTIVES

Although recognized for decades, little is known about the etiology, physiopathology, and prevention of persistent pulmonary hypertension of the newborn (PPHN), and its treatment remains a major challenge for neonatologists. In this review, the clinical features and physiopathology of the syndrome will be addressed, as well as its general and specific treatments.

DATA SOURCE

A review was carried out in PubMed, Cochrane Library, and MRei consult databases, searching for articles related to the syndrome and published between 1995 and 2011.

DATA SYNTHESIS

Risk factors and the physiopathological mechanisms of the syndrome are discussed. The clinical presentation depends on the different factors involved. These are related to the etiology and physiopathology of the different forms of the disease. In addition to the measures used to allow for the decrease in pulmonary vascular resistance after birth, in some instances pulmonary vasodilators will be required. Although inhaled nitric oxide has proved effective, other vasodilators have been recently used, but clinical evidence is still lacking to demonstrate their benefits in the treatment of PPHN.

CONCLUSIONS

Despite recent technological advances and new physiopathological knowledge of this disease, mortality associated with PPHN remains at 10%. More clinical research and evidence-based experimental results are needed to prevent, treat, and reduce the morbidity/mortality associated with this neonatal syndrome.

Pulmonary hypertension in bronchopulmonary dysplasia

Pulmonary hypertension (PH) is a common complication of neonatal respiratory diseases, including bronchopulmonary dysplasia (BPD), and recent studies have increased awareness that PH worsens the clinical course, morbidity and mortality of BPD. Recent evidence indicates that up to 18% of all extremely low-birth-weight infants will develop some degree of PH during their hospitalization, and the incidence rises to 25-40% of the infants with established BPD. Risk factors are not yet well understood, but new evidence shows that fetal growth restriction is a significant predictor of PH. Echocardiography remains the primary method for evaluation of BPD-associated PH, and the development of standardized screening timelines and techniques for identification of infants with BPD-associated PH remains an important ongoing topic of investigation. The use of pulmonary vasodilator medications, such as nitric oxide, sildenafil, and others, in the BPD population is steadily growing, but additional studies are needed regarding their long-term safety and efficacy.

Pharmacotherapy for pulmonary hypertension

Pulmonary arterial hypertension is a serious disease with significant morbidity and mortality. Although it can occur idiopathically, it is more commonly associated with other cardiac or lung diseases. While most of the available therapies have been tested in adult populations and most therapies in children remain off-label, new reports and randomized trials are emerging that inform the treatment of pediatric populations. This review discusses currently available therapies for pediatric pulmonary hypertension, their biological rationales, and evidence for their clinical effectiveness.

The pulmonary circulation in neonatal respiratory failure

The pulmonary circulation rapidly adapts at birth to establish lungs as the site of gas exchange. Abnormal transition at birth and/or parenchymal lung disease can result in neonatal hypoxemic respiratory failure. This article reviews the functional changes in pulmonary hemodynamics and structural changes in pulmonary vasculature secondary to (1) normal and abnormal transition at birth, and (2) diseases associated with neonatal hypoxemic respiratory failure. Various management strategies to correct respiratory failure are also discussed.

Molecular mechanisms regulating the vascular prostacyclin pathways and their adaptation during pregnancy and in the newborn

Prostacyclin (PGI(2)) is a member of the prostanoid group of eicosanoids that regulate homeostasis, hemostasis, smooth muscle function and inflammation. Prostanoids are derived from arachidonic acid by the sequential actions of phospholipase A(2), cyclooxygenase (COX), and specific prostaglandin (PG) synthases. There are two major COX enzymes, COX1 and COX2, that differ in structure, tissue distribution, subcellular localization, and function. COX1 is largely constitutively expressed, whereas COX2 is induced at sites of inflammation and vascular injury. PGI(2) is produced by endothelial cells and influences many cardiovascular processes. PGI(2) acts mainly on the prostacyclin (IP) receptor, but because of receptor homology, PGI(2) analogs such as iloprost may act on other prostanoid receptors with variable affinities. PGI(2)/IP interaction stimulates G protein-coupled increase in cAMP and protein kinase A, resulting in decreased [Ca(2+)](i), and could also cause inhibition of Rho kinase, leading to vascular smooth muscle relaxation. In addition, PGI(2) intracrine signaling may target nuclear peroxisome proliferator-activated receptors and regulate gene transcription. PGI(2) counteracts the vasoconstrictor and platelet aggregation effects of thromboxane A(2) (TXA(2)), and both prostanoids create an important balance in cardiovascular homeostasis. The PGI(2)/TXA(2) balance is particularly critical in the regulation of maternal and fetal vascular function during pregnancy and in the newborn. A decrease in PGI(2)/TXA(2) ratio in the maternal, fetal, and neonatal circulation may contribute to preeclampsia, intrauterine growth restriction, and persistent pulmonary hypertension of the newborn (PPHN), respectively. On the other hand, increased PGI(2) activity may contribute to patent ductus arteriosus (PDA) and intraventricular hemorrhage in premature newborns. These observations have raised interest in the use of COX inhibitors and PGI(2) analogs in the management of pregnancy-associated and neonatal vascular disorders. The use of aspirin to decrease TXA(2) synthesis has shown little benefit in preeclampsia, whereas indomethacin and ibuprofen are used effectively to close PDA in the premature newborn. PGI(2) analogs have been used effectively in primary pulmonary hypertension in adults and have shown promise in PPHN. Careful examination of PGI(2) metabolism and the complex interplay with other prostanoids will help design specific modulators of the PGI(2)-dependent pathways for the management of pregnancy-related and neonatal vascular disorders.

Pulmonary vasodilator therapy in the NICU: inhaled nitric oxide, sildenafil, and other pulmonary vasodilating agents

The perinatal transition from fetal to extrauterine life requires a dramatic change in the circulatory pattern as the organ of gas exchange switches from the placenta to the lungs. Pulmonary hypertension can occur during early newborn life, and present as early respiratory failure or as a complication of more chronic diseases, such as bronchopulmonary dysplasia. The most effective pharmacotherapeutic strategies for infants with persistent pulmonary hypertension of the newborn are directed at selective reduction of pulmonary vascular resistance. This article discusses currently available therapies for pulmonary hypertension, their biologic rationales, and evidence for their clinical effectiveness.

Milrinone attenuates thromboxane receptor-mediated hyperresponsiveness in hypoxic pulmonary arterial myocytes

BACKGROUND AND PURPOSE

Neonatal pulmonary hypertension (PPHN) is characterized by pulmonary vasoconstriction, due in part to dysregulation of the thromboxane prostanoid (TP) receptor. Hypoxia induces TP receptor-mediated hyperresponsiveness, whereas serine phosphorylation mediates desensitization of TP receptors. We hypothesized that prostacyclin (IP) receptor activity induces TP receptor phosphorylation and decreases ligand affinity; that TP receptor sensitization in hypoxic myocytes is due to IP receptor inactivation; and that this would be reversible by the cAMP-specific phosphodiesterase inhibitor milrinone.

EXPERIMENTAL APPROACH

We examined functional regulation of TP receptors by serine phosphorylation and effects of IP receptor stimulation and protein kinase A (PKA) activity on TP receptor sensitivity in myocytes from neonatal porcine resistance pulmonary arteries after 72 h hypoxia in vitro. Ca(2+) response curves to U46619 (TP receptor agonist) were determined in hypoxic and normoxic myocytes incubated with or without iloprost (IP receptor agonist), forskolin (adenylyl cyclase activator), H8 (PKA inhibitor) or milrinone. TP and IP receptor saturation binding kinetics were measured in presence of iloprost or 8-bromo-cAMP.

KEY RESULTS

Ligand affinity for TP receptors was normalized in vitro by IP receptor signalling intermediates. However, IP receptor affinity was compromised in hypoxic myocytes, decreasing cAMP production. Milrinone normalized TP receptor sensitivity in hypoxic myocytes by restoring PKA-mediated regulatory TP receptor phosphorylation.

CONCLUSIONS AND IMPLICATIONS

TP receptor sensitivity and EC(50) for TP receptor agonists was regulated by PKA, as TP receptor serine phosphorylation by PKA down-regulated Ca(2+) mobilization. Hypoxia decreased IP receptor activity and cAMP generation, inducing TP receptor hyperresponsiveness, which was reversed by milrinone.

Phosphodiesterases: emerging therapeutic targets for neonatal pulmonary hypertension

Pulmonary hypertension in the neonate is associated with multiple underlying problems such as respiratory distress syndrome, meconium aspiration syndrome, congenital diaphragmatic hernia, bronchopulmonary dysplasia, sepsis, or congenital heart disease. Because of the heterogeneous group of disorders, the therapeutic approach and response often depends on the underlying disease. In many of these conditions, there is evidence that cyclic nucleotide signaling and specifically phosphodiesterases (PDEs) are disrupted. PDE inhibitors represent an emerging class of pulmonary vasodilators in adults. Studies are now under way to evaluate the utility, efficacy, and safety of such therapies in infants with pulmonary hypertension.

Current and future therapeutic options for persistent pulmonary hypertension in the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is a potentially life-threatening condition that is characterized by supra-systemic pulmonary vascular resistance causing right-to-left shunting through the ductus arteriosus and/or foramen ovale, leading to a vicious cycle of hypoxemia, acidosis and further pulmonary vasoconstriction. Advances in neonatology including surfactant instillation, high-frequency ventilation, extracorporeal membrane oxygenation and, most importantly, inhaled nitric oxide (INO), have revolutionized the management of PPHN. However, given that INO does not improve oxygenation in a significant proportion (30-40%) of cases, there is an urgent need to consider other therapeutic options for PPHN. The issue is more important for developing nations with a higher PPHN-related health burden and limited resources. This article discusses the evidence about INO in term and preterm neonates in brief, and focuses mainly on the potential alternative drugs in the management of PPHN.