Pulmonary hypertension in children: the twenty-first century

Pharmacotherapy in Bronchopulmonary Dysplasia: What Is the Evidence?

Bronchopulmonary Dysplasia (BPD) is a multifactorial disease affecting over 35% of extremely preterm infants born each year. Despite the advances made in understanding the pathogenesis of this disease over the last five decades, BPD remains one of the major causes of morbidity and mortality in this population, and the incidence of the disease increases with decreasing gestational age. As inflammation is one of the key drivers in the pathogenesis, it has been targeted by majority of pharmacological and non-pharmacological methods to prevent BPD. Most extremely premature infants receive a myriad of medications during their stay in the neonatal intensive care unit in an effort to prevent or manage BPD, with corticosteroids, caffeine, and diuretics being the most commonly used medications. However, there is no consensus regarding their use and benefits in this population. This review summarizes the available literature regarding these medications and aims to provide neonatologists and neonatal providers with evidence-based recommendations.

Gestational Hypoxia and Programing of Lung Metabolism

Gestational hypoxia is a risk factor in the development of pulmonary hypertension in the newborn and other sequela, however, the mechanisms associated with the disease remain poorly understood. This review highlights disruption of metabolism by antenatal high altitude hypoxia and the impact this has on pulmonary hypertension in the newborn with discussion of model organisms and human populations. There is particular emphasis on modifications in glucose and lipid metabolism along with alterations in mitochondrial function. Additional focus is placed on increases in oxidative stress and the progression of pulmonary vascular disease in the newborn and on the need for further exploration using a combination of contemporary and classical approaches.

Pharmacotherapy for the Prevention of Bronchopulmonary Dysplasia: Can Anything Compete with Caffeine and Corticosteroids?

Bronchopulmonary dysplasia (BPD) is a morbidity of prematurity with implications for respiratory and neurologic health into adulthood. Multiple risk factors contribute to the development of BPD leading to examination of various prevention strategies. The roles of systemic corticosteroids and caffeine have been addressed by the American Academy of Pediatrics. The place in therapy of other agents commonly utilized in clinical practice remains unclear. Inhaled nitric oxide has been the subject of numerous large, randomized controlled trials in preterm infants. Despite sound rationale, these trials have largely failed to document benefit, suggesting a limited role for inhaled nitric oxide therapy in the preterm population. In contrast, intramuscular vitamin A has been documented to reduce the incidence of BPD in randomized trials. However, the invasiveness and the sporadic availability of this therapy have led to decreased utilization. All macrolide antibiotics do not appear to have a similar impact on the incidence of BPD; however, azithromycin administered to infants colonized with Ureaplasma may have impact. Questions remain about the optimal dosing approach and long-term safety of this intervention. Finally, diuretic therapy is widely used in clinical practice despite significant toxicities and limited data supporting a role in BPD prevention. Taken together, available data suggest that caffeine and selective use of corticosteroids remain the mainstays of pharmacologic BPD prevention.

Treatment of Persistent Pulmonary Hypertension of the Newborn: Use of Pulmonary Vasodilators in Term Neonates

Persistent pulmonary hypertension of the newborn (PPHN) represents a challenging condition associated with significant morbidity. A successful transition from intrauterine to extrauterine life is contingent on adequate pulmonary vasodilation. Several pathophysiologies contribute to the failure of this cascade and may result in life-threatening hypoxia and acidosis in the newborn. Management includes optimal respiratory support, adequate sedation and analgesia, and support of vascular tone and cardiac function. Pulmonary vasodilation has the potential to overcome the cycle of hypoxia and acidosis, improving outcome in these infants. Oxygen and inhaled nitric oxide represent the foundation of therapy. Tertiary pulmonary vasodilators represent a greater challenge, selecting between therapies that include prostanoids, sildenafil, and milrinone. Variable levels of evidence exist for each agent. Thorough review of available data informing efficacy and adverse effects contributes to the development of an informed approach to neonates with refractory PPHN.

Thromboxane promotes smooth muscle phenotype commitment but not remodeling of hypoxic neonatal pulmonary artery

Background

Persistent pulmonary hypertension of the newborn (PPHN) is characterized by vasoconstriction and pulmonary vascular remodeling. Remodeling is believed to be a response to physical or chemical stimuli including pro-mitotic inflammatory mediators such as thromboxane. Our objective was to examine the effects of hypoxia and thromboxane signaling ex vivo and in vitro on phenotype commitment, cell cycle entry, and proliferation of PPHN and control neonatal pulmonary artery (PA) myocytes in tissue culture.

Methods

To examine concurrent effects of hypoxia and thromboxane on myocyte growth, serum-fed first-passage newborn porcine PA myocytes were randomized into normoxic (21 % O₂) or hypoxic (10 % O₂) culture for 3 days, with daily addition of thromboxane mimetic U46619 (10⁻⁹ to 10⁻⁵ M) or diluent. Cell survival was detected by MTT assay. To determine the effect of chronic thromboxane exposure (versus whole serum) on activation of arterial remodeling, PPHN was induced in newborn piglets by a 3-day hypoxic exposure (FiO₂ 0.10); controls were 3 day-old normoxic and day 0 piglets. Third-generation PA were segmented and cultured for 3 days in physiologic buffer, Ham’s F-12 media (in the presence or absence of 10 % fetal calf serum), or media with 10⁻⁶ M U46619. DNA synthesis was measured by ³H-thymidine uptake, protein synthesis by ³H-leucine uptake, and proliferation by immunostaining for Ki67. Cell cycle entry was studied by laser scanning cytometry of nuclei in arterial tunica media after propidium iodide staining. Phenotype commitment was determined by immunostaining tunica media for myosin heavy chain and desmin, quantified by laser scanning cytometry.

Results

Contractile and synthetic myocyte subpopulations had differing responses to thromboxane challenge. U46619 decreased proliferation of synthetic and contractile myocytes. PPHN arteries exhibited decreased protein synthesis under all culture conditions. Serum-supplemented PA treated with U46619 had decreased G1/G0 phase myocytes and an increase in S and G2/M. When serum-deprived, PPHN PA incubated with U46619 showed arrested cell cycle entry (increased G0/G1, decreased S and G2/M) and increased abundance of contractile phenotype markers.

Conclusions

We conclude that thromboxane does not initiate phenotypic dedifferentiation and proliferative activation in PPHN PA. Exposure to thromboxane triggers cell cycle exit and myocyte commitment to contractile phenotype.

Pulmonary functions before and after pediatric cardiac surgery

This study aimed to assess pulmonary functions before and after cardiac surgery in infants with congenital heart diseases and pulmonary overflow and to clarify which echocardiographic parameter correlates best with lung mechanics. Between 2008 and 2009, 30 infants with left-to-right shunt congenital acyanotic heart diseases who had indications for reparative surgery of these lesions were assessed by echocardiography and infant pulmonary function tests before the operation and 6 months afterward. Tests using baby body plethysmography were performed to assess the following infant pulmonary functions: tidal volume, respiratory rate, respiratory system compliance (C(rs)) and respiratory system resistance, functional residual capacity (FRC), and airway resistance. The mean age of the patients was 10.47 ± 3.38 months, and their mean weight was 6.81 ± 1.67 kg. Ventricular septal defect and combined lesions were the predominant cardiac diseases (26.7%). Comparison of the infant pulmonary function tests showed a highly significant improvement in all the parameters between the preoperative and 6-month postoperative visits (p < 0.0001). Systolic pulmonary artery pressure had a statistically significant negative correlation with C(rs) (r = -0.493, p = 0.006) and a positive correlation with FRC (r = 0.450, p = 0.013). The findings showed that C(rs) had a statistically significant negative correlation with the pulmonary artery size (r = -0.398, p = 0.029) and the left atrium size (r = -0.395, p = 0.031), whereas the pulmonary artery size had a statistically positive correlation with effective resistance (r = 0.416, p = 0.022) and specific effective resistance (r = 0.604, p = 0.0001). Surgical correction of left-to-right shunt congenital heart diseases had a positive impact on lung compliance, airway resistance, and FRC. Noninvasive echocardiographic parameters assessing pulmonary vascular engorgement and pulmonary artery pressure were closely related to these infant pulmonary function test indexes.

Pulmonary hypertension: a review of pathophysiology and anesthetic management

Pulmonary hypertension is a condition that can result in serious complications in patients undergoing any type of anesthesia during the perioperative period. By definition, pulmonary artery hypertension is caused by a persistent rise in mean pulmonary artery pressure ≥25 mm Hg with Pulmonary capillary wedge pressure ≤ 15 mm Hg or exercise mean pulmonary artery pressure ≥35 mm Hg and pulmonary vascular resistance ≥ 3 wood unit's. The severity of the complications depends on the severity of the underlying condition, other comorbidities, and type of procedure, anesthetic technique, and anesthetic drugs. In this article, we briefly review the pulmonary vascular physiology, pathophysiology of the disease, clinical assessment and diagnosis, treatment options, and the anesthetic management of these patients.

Recommendations for long-term home oxygen therapy in children and adolescents

OBJECTIVE

To advise pediatricians, neonatologists, pulmonologists, pediatric pulmonologists, and other professionals in the area on the main indications and characteristics of long-term home oxygen therapy in children and adolescents.

DATA SOURCE

A literature search was carried out in the MEDLINE/PubMed database (1990 to 2011). Additionally, references from selected studies were included. As consistent scientific evidence does not exist for many aspects, some of the recommendations were based on clinical experience.

DATA SYNTHESIS

Long-term home oxygen therapy has been a growing practice in pediatric patients and is indicated in bronchopulmonary dysplasia, cystic fibrosis, bronchiolitis obliterans, interstitial lung diseases, and pulmonary hypertension, among others. The benefits are: decrease in hospitalizations, optimization of physical growth and neurological development, improvement of exercise tolerance and quality of sleep, and prevention of pulmonary hypertension/cor pulmonale. The levels of oxygen saturation indicative for oxygen therapy differ from those established for adults with chronic obstructive pulmonary disease, and vary according to age and disease. Pulse oximetry is used to evaluate oxygen saturation; arterial blood gas is unnecessary. There are three available sources of oxygen: gas cylinders, liquid oxygen, and oxygen concentrators. The flows used are usually smaller, as are the number of hours/day needed when compared to the use in adults. Some diseases show improvement and oxygen therapy discontinuation is possible.

CONCLUSIONS

Long-term home oxygen therapy is increasingly common in pediatrics and has many indications. There are relevant particularities when compared to its use in adults, regarding indications, directions for use, and monitoring.

Hypoxia and nitric oxide exposure promote apoptotic signaling in contractile pulmonary arterial smooth muscle but not in pulmonary epithelium

RATIONALE

Neonatal pulmonary hypertension is characterized by hypoxia, abnormal vascular remodeling, and impaired alveolarization. Nitric oxide (NO) regulates cell replication and activation of apoptosis. Our objective was to examine cell phenotype-specific effects of hypoxia and NO exposure on cumulative apoptotic signal in neonatal pulmonary epithelial cells and arterial smooth muscle.

DESIGN/METHODS

Primary cultured newborn porcine pulmonary arterial myocytes and epithelial cells were grown in normoxic (21% O2) or hypoxic conditions (10% O2). Myocyte phenotype was predetermined by serum-supplementation or -deprivation. Cells were exposed to sodium nitroprusside (10(-7) -10(-4)  M) or diluent for 3 days. Cell survival was estimated by MTT assay; BAX, Bcl-2, and cleaved caspase-3 by Western blot; cell cycle entry by laser scanning cytometry.

RESULTS

Hypoxic epithelial cells exhibited a small increase in anti-apoptotic Bcl2, and decrease in BAX. Cell survival and active caspase-3 were unchanged. Exposure to NO had no impact on epithelial apoptosis, but initiated necrosis. In contractile myocytes, pro-apoptotic BAX abundance and caspase-3 activation were increased by hypoxia, augmented by NO exposure promoting apoptosis. Hypoxia decreased BAX/Bcl-2 ratio and promoted survival of synthetic myocytes; NO increased apoptosis of normoxic synthetic myocytes, but decreased apoptosis of hypoxic synthetic myocytes.

CONCLUSION

The effect of NO on pulmonary apoptosis is phenotype-dependent. A cumulative apoptotic effect of hypoxia and NO in vitro exerted on contractile myocytes may lead to contraction of this subpopulation, while synthetic myocyte survival and proliferation is enhanced by hypoxia and NO. Epithelial survival is unaffected. We speculate that alveolar rarefaction reported after neonatal hypoxia may arise from growth arrest in the vascular rather than the epithelial compartment.

Pulmonary artery catheters

BACKGROUND

After its introduction in 1970, the use of the pulmonary artery catheter became a central part of the management of critically ill patients in adult and pediatric intensive care units. However, because it was introduced as a class II device, efficacy for its safety and clinical benefit did not exist during the early years of use. This review describes the pulmonary artery catheter and reviews the literature supporting its use.

METHODOLOGY

A search of MEDLINE, PubMed, and the Cochrane Database was made to find literature about pulmonary artery catheter use. Literature for both adult and pediatric patients was reviewed. Guidelines published by the Society for Critical Care Medicine and the American Heart Association were reviewed, including further review of references cited.

RESULTS AND CONCLUSIONS

The evidence supporting the use of the pulmonary artery catheter is mostly limited to level IV (nonrandomized, historical controls, and expert opinion) and level V (case series, uncontrolled studies, and expert opinion). A higher level of evidence supports the use of the pulmonary artery catheter in selected pediatric patients, especially those with pulmonary arterial hypertension and shock refractory to standard fluid resuscitation and vasoactive agents. There are no data to suggest that use of the pulmonary artery catheter increases mortality in children.

High prevalence of minor neurologic deficits in a long-term neurodevelopmental follow-up of children with severe persistent pulmonary hypertension of the newborn: a cohort study

BACKGROUND

Persistent pulmonary hypertension of the newborn (PPHN) is a severe condition that determines a profound brain hypoxia. Inhaled nitric oxide was approved for the treatment of PPHN since the end of the 1990s. The debate upon the long term outcome of these children is still open. Our aim was to investigate the incidence of minor long-term neurodevelopmental problems in a cohort of children affected by severe PPHN.

METHODS

All neonates with severe PPHN treated with inhaled nitric oxide in our facility between 01.01.02 and 31.12.07 were seen in a follow up visit and evaluated with a neurodevelopmental scale, according to their age at the time of observation.

RESULTS

in the study period 31 children were diagnosed with severe PPHN. 29 survived. 27 accepted to come for follow-up. Mean age: 41 months (range 12 - 70 months).26% of the evaluated children had some behavioural problems, while 22% had some language disturbances.

CONCLUSIONS

This is the first neurodevelopmental follow-up of neonates with PPHN in which children older than 36 months have been evaluated.There is an unexpected high incidence of minor neurological deficits, mainly regarding the fields of language and behaviour. These deficits seem to be related to the severity of illness rather than to the treatment. Language and behaviour are considered "higher functions" in humans and their integrity can be better defined in older children.

Methemoglobin to cumulative nitric oxide ratio and response to inhaled nitric oxide in PPHN

BACKGROUND

One-third of infants with persistent pulmonary hypertension of the newborn (PPHN) do not respond to inhaled nitric oxide (iNO). If iNO is not delivered to the pulmonary vasculature because of parenchymal lung disease, it cannot interact with hemoglobin to form methemoglobin (MHb).

OBJECTIVE

To study the correlation between oxygenation response to iNO in infants with PPHN secondary to parenchymal lung disease and initial MHb% to cumulative NO exposure (ppm x hours) ratio (MHb/SigmaNO).

STUDY DESIGN

Retrospective chart review of neonates with PPHN secondary to parenchymal lung disease treated with iNO comparing non-responders (PaO(2)/FiO(2) ratio<10 change with iNO) with responders (>or=10 change).

RESULT

Non-responders (n=16) had a PaO(2)/F(iO2) of 83+/-48 (mean+/-s.d.) and decreased to 74+/-44 after iNO. PaO(2)/FiO(2) increased from 70+/-48 to 151+/-63 with iNO among responders (n=36). The MHb/SigmaNO ratio was low (0.024+/-0.012) among non-responders compared with responders (0.07+/-0.053, P<0.005).

CONCLUSION

Inadequate oxygenation response to iNO is associated with lower MHb/SigmaNO, suggesting suboptimal delivery of iNO to the pulmonary vasculature.

Pediatric Pulmonary Hypertension: A Pharmacotherapeutic Review

Pulmonary hypertension in children is a disorder associated with increased pulmonary vascular resistance and arterial pressure, decreased cardiac output, and right-sided cardiac dysfunction that is caused by numerous etiologies. Although treatment will vary with underlying cause, pharmacological treatment has historically included inhaled nitric oxide and prostacyclin analogues. Over the past several years new agents have been added to the treatment armamentarium, including phosphodiesterase V inhibitors (eg sildenafil) and endothelin antagonists (eg bosentan). Further, more agents are currently under investigation for pulmonary hypertension in children including immunosuppressives and other endothelin antagonist entities. Limitations to treatment include the availability of appropriate, robust pediatric pharmacological data and constraints with dosage forms.

Pulmonary hypertension in children with Evans syndrome

Evans syndrome is a rare cause of hemolysis in pediatric patients. The authors describe two severely affected patients who had previously been heavily treated, and who subsequently developed severe pulmonary hypertension. Both patients were successfully managed by a combination of immunosuppression and anti-pulmonary hypertension treatment. The first patient to present, case A, received an allogeneic bone marrow transplant with subsequent cure of both Evans syndrome and pulmonary hypertension and is now on a weaning dose of sildenafil. Case B is being worked up for allogeneic bone marrow transplantation. The authors speculate that the pulmonary hypertension was caused by the underlying immune dysregulation and hemolysis and that Evans syndrome joins the list of other hemolytic anemias that cause pulmonary hypertension, such as sickle cell disease, thalassemia, and paroxysmal nocturnal hemoglobinuria. However, they suggest a vasculitic process as the main cause.

Therapeutic lung lavage with diluted surfactant in neonates with severe meconium aspiration syndrome

Meconium aspiration syndrome (MAS) may result in considerable morbidity and mortality in newborn infants. The current standard treatment is still in need of improvement for the most severe patients. We report 3 cases with devastating MAS that was successfully treated with therapeutic lung lavage. These cases were all delivered in local obstetrics clinics or hospitals with meconium-stained amniotic fluid and non-vigorous appearance at birth. However, no endotracheal suction was performed when they were born. All of them suffered from severe hypoxia and unstable vital signs despite there being high ventilatory settings when they were transferred to the tertiary medical center. Therapeutic lung lavage with diluted surfactant (Survanta, 5 mg/mL, 30 mL/kg in 2 aliquots) was performed within 24 hours of age. Bloody fluid (about 40-50% of total lavage amount) was recovered in all 3 cases. Although brief desaturation and bradycardia were observed during the procedures, 2 of them tolerated the procedures well and improved soon after lavage. The other patient received lung lavage in a relatively unstable condition and needed chest tapping to relieve bilateral pleural effusion. Their respiratory condition improved after the procedures, and they were all discharged within 1 month without major respiratory complications. These successful experiences are compatible with previous animal studies and other case reports with different lavage protocols. We conclude that therapeutic lung lavage may improve the outcome in newborn infants with severe MAS, and there were no significant adverse side effects observed. Before performing lung lavage, stabilization and optimal support may prevent unexpected results during and after lavage.