Improved oxygenation in a randomized trial of inhaled nitric oxide for persistent pulmonary hypertension of the newborn

Comparison of Different Treatments of Persistent Pulmonary Hypertension of the Newborn: A Systematic Review and Network Meta-Analysis

OBJECTIVES

Persistent pulmonary hypertension of the newborn (PPHN) is a life-threatening disease. Despite being considered the gold standard treatment scheme, inhaled nitric oxide (iNO) is not readily available in settings with limited resources. Therefore, in recent years, research on related drugs is being actively pursued. Herein, we aimed to use random-effects network meta-analysis to evaluate the efficacy and associated mortality of different PPHN therapies.

DATA SOURCES

We electronically searched the PubMed, Embase, and Cochrane Library for data up to January 27, 2023.

STUDY SELECTION

Randomized controlled trials involving neonates with PPHN assessing efficacy and mortality of various treatments.

DATA EXTRACTION

Details of study population, treatments, and outcomes were extracted.

DATA SYNTHESIS

Direct pairwise comparisons and a network meta-analysis was performed under random effects. The ranking probability was further assessed based on the surface under the cumulative ranking curve (SUCRA). We analyzed 23 randomized clinical trials involving 902 newborns with PPHN. Sixteen different treatment strategies were compared with each other and conventional therapy (CON). A median concentration of 10-20 parts per million (ppm) iNO (MNO) coupled with sildenafil orally administered at a dose of 1-3 mg/kg/dose every 6-8 hours (OSID) demonstrated the best efficacy (MNO + OSID vs. CON: odds ratio [OR] = 27.53, 95% CI, 2.36-321.75; SUCRA = 0.818, ranking first; moderate quality). OSID combined with milrinone administered IV also performed well in terms of efficacy (OSID + milrinone vs. CON: OR = 25.13, 95% CI = 1.67-377.78; SUCRA = 0.811, ranking second; low quality) and mortality reduction (CON vs. OSID + milrinone: OR = 25.13, 95% CI = 1.67-377.78; SUCRA = 0.786, ranking last; low quality).

CONCLUSIONS

MNO + OSID is the most effective PPHN treatment. If iNO is not available, OSID + milrinone is preferred.

Computational Insights on Structural Sensitivity of Cobalt in NO Electroreduction to Ammonia and Hydroxylamine

It has been reported that it was selective to produce ammonia on metallic cobalt in the electrocatalytic nitric oxide reduction reaction (eNORR), where hexagonal close-packed (hcp) cobalt outperforms face-centered cubic (fcc) cobalt. However, hydroxylamine is more selectively produced on a cobalt single-atom catalyst (Co-SAC). Herein, we uncover the structural sensitivity over hcp-Co, fcc-Co, and Co-SAC in eNORR by employing a recently developed constant potential simulation method and microkinetic modeling. It was found that the superior activity for ammonia production on hcp-Co can be attributed to its facile electron and proton transfer and a stronger lateral suppression effect from NO* over fcc-Co. The exceptional hydroxylamine selectivity on Co-SAC is due to the modified electronic structure, namely, a positively charged active center. It was found that it is more favorable to produce NOH* over hcp-Co and fcc-Co, while HNO* is more preferable on Co-SAC, which are firmly correlated with the vertical and strong NO adsorption on the former and the moderate adsorption on the latter. In other words, a key factor for selectivity control is the first step of NO* protonation. Therefore, the local structure and electronic structure of the catalysts can be critical in regulating the activity and selectivity in eNORR.

Meconium aspiration syndrome: from pathophysiology to treatment

Meconium aspiration syndrome (MAS) is a clinical condition characterized by respiratory distress in neonates born through meconium-stained amniotic fluid (MSAF). Despite advances in obstetric practices and perinatal care, MAS remains an important cause of morbidity and mortality in term and post-term newborns. Since the 1960s, there have been significant changes in the perinatal and postnatal management of infants born through MSAF. Routine endotracheal suctioning is no longer recommended in both vigorous and non-vigorous neonates with MSAF. Supportive care along with new treatments such as surfactant, inhaled nitric oxide, and high-frequency ventilation has significantly improved the outcome of MAS patients. However, determining the most appropriate approach for this condition continues to be a topic of debate. This review offers an updated overview of the epidemiology, etiopathogenesis, diagnosis, management, and prognosis of infants with MAS.

Echocardiographic Assessment of Pulmonary Arterial Hypertension Following Inhaled Nitric Oxide in Infants with Severe Bronchopulmonary Dysplasia

OBJECTIVES

Inhaled nitric oxide (iNO) is an effective pulmonary vasodilator. However, the efficacy of iNO in former premature infants with established bronchopulmonary dysplasia (BPD) has not been studied. This study aimed to determine the efficacy of iNO in reducing pulmonary artery pressure in infants with severe BPD as measured by echocardiography.

STUDY DESIGN

Prospective, observational study enrolling infants born at less than 32 weeks gestation and in whom (1) iNO therapy was initiated after admission to our institution, or (2) at the outside institution less than 48 h before transfer and received an echocardiogram prior to iNO initiation, and (3) had severe BPD. Data were collected at three time-points: (1) before iNO; (2) 12-48 h after initiation of iNO; and (3) 48-168 h after initiation of iNO. The primary outcome was the effect of iNO on pulmonary artery pressure measured by echocardiography in patients with severe BPD between 48 and 168 h after initiating iNO therapy.

RESULTS

Of 37 enrolled, 81% had echocardiographic evidence of pulmonary arterial hypertension (PAH) before iNO and 56% after 48 h of iNO (p = 0.04). FiO2 requirements were significantly different between time-points (1) and (3) (p = 0.05). There were no significant differences between Tricuspid Annular Plane Systolic Excursion (TAPSE) Z-Scores, time to peak velocity: right ventricular ejection time (TPV:RVET), and ventilator changes.

CONCLUSIONS

Although we found a statistically significant reduction of PAH between time-point (1) and (3), future trials are needed to further guide clinical care.

Nitric oxide: Clinical applications in critically ill patients

Inhaled nitric oxide (iNO) acts as a selective pulmonary vasodilator and it is currently approved by the FDA for the treatment of persistent pulmonary hypertension of the newborn. iNO has been demonstrated to effectively decrease pulmonary artery pressure and improve oxygenation, while decreasing extracorporeal life support use in hypoxic newborns affected by persistent pulmonary hypertension. Also, iNO seems a safe treatment with limited side effects. Despite the promising beneficial effects of NO in the preclinical literature, there is still a lack of high quality evidence for the use of iNO in clinical settings. A variety of clinical applications have been suggested in and out of the critical care environment, aiming to use iNO in respiratory failure and pulmonary hypertension of adults or as a preventative measure of hemolysis-induced vasoconstriction, ischemia/reperfusion injury and as a potential treatment of renal failure associated with cardiopulmonary bypass. In this narrative review we aim to present a comprehensive summary of the potential use of iNO in several clinical conditions with its suggested benefits, including its recent application in the scenario of the COVID-19 pandemic. Randomized controlled trials, meta-analyses, guidelines, observational studies and case-series were reported and the main findings summarized. Furthermore, we will describe the toxicity profile of NO and discuss an innovative proposed strategy to produce iNO. Overall, iNO exhibits a wide range of potential clinical benefits, that certainly warrants further efforts with randomized clinical trials to determine specific therapeutic roles of iNO.

Pediatric Pulmonary Hypertension: Definitions, Mechanisms, Diagnosis, and Treatment

Pediatric pulmonary hypertension (PPH) is a multifactorial disease with diverse etiologies and presenting features. Pulmonary hypertension (PH), defined as elevated pulmonary artery pressure, is the presenting feature for several pulmonary vascular diseases. It is often a hidden component of other lung diseases, such as cystic fibrosis and bronchopulmonary dysplasia. Alterations in lung development and genetic conditions are an important contributor to pediatric pulmonary hypertensive disease, which is a distinct entity from adult PH. Many of the causes of pediatric PH have prenatal onset with altered lung development due to maternal and fetal conditions. Since lung growth is altered in several conditions that lead to PPH, therapy for PPH includes both pulmonary vasodilators and strategies to restore lung growth. These strategies include optimal alveolar recruitment, maintaining physiologic blood gas tension, nutritional support, and addressing contributing factors, such as airway disease and gastroesophageal reflux. The outcome for infants and children with PH is highly variable and largely dependent on the underlying cause. The best outcomes are for neonates with persistent pulmonary hypertension (PPHN) and reversible lung diseases, while some genetic conditions such as alveolar capillary dysplasia are lethal. © 2021 American Physiological Society. Compr Physiol 11:2135-2190, 2021.

Meconium Aspiration Syndrome: A Narrative Review

Meconium aspiration syndrome is a clinical condition characterized by respiratory failure occurring in neonates born through meconium-stained amniotic fluid. Worldwide, the incidence has declined in developed countries thanks to improved obstetric practices and perinatal care while challenges persist in developing countries. Despite the improved survival rate over the last decades, long-term morbidity among survivors remains a major concern. Since the 1960s, relevant changes have occurred in the perinatal and postnatal management of such patients but the most appropriate approach is still a matter of debate. This review offers an updated overview of the epidemiology, etiopathogenesis, diagnosis, management and prognosis of infants with meconium aspiration syndrome.

Variation in the definition of pulmonary hypertension and clinical indications for the use of nitric oxide in neonatal clinical trials

AIM

Pulmonary hypertension (PH) frequently complicates neonatal hypoxaemic respiratory failure, but is inconsistently defined. We aimed to describe the variation among randomised controlled trials (RCTs) of inhaled nitric oxide (iNO), in relation to the definition of PH and/or hypoxaemic respiratory failure used to select patients for trial inclusion.

METHODS

PubMed, Cochrane Library and ClinicalTrials.gov were systematically searched for RCTs of iNO in neonates. Included studies were assessed for clinical and/or echocardiography criteria used to define PH/hypoxaemic respiratory failure.

RESULTS

Thirty-two trials were included in this review, of which 23 enrolled infants ≥34 weeks' gestation. Echocardiographic diagnosis was used in 21 studies, but there was considerable variation in the echocardiographic parameters used to diagnose PH. The most commonly used indices included markers of tricuspid regurgitation and extrapulmonary shunt.

CONCLUSION

There is wide variation in the definition of PH used to select infants for inclusion into RCTs of iNO therapy in neonates. We recommend that an international consensus be reached on which parameters should be used and the thresholds defining severity of disease.

Drug Treatment of Pulmonary Hypertension in Children

Pulmonary arterial hypertension (PAH) is a rare disease in infants and children that is associated with significant morbidity and mortality. The disease is characterized by progressive pulmonary vascular functional and structural changes resulting in increased pulmonary vascular resistance and eventual right heart failure and death. In many pediatric patients, PAH is idiopathic or associated with congenital heart disease and rarely is associated with other conditions such as connective tissue or thromboembolic disease. PAH associated with developmental lung diseases such as bronchopulmonary dysplasia or congenital diaphragmatic hernia is increasingly more recognized in infants and children. Although treatment of the underlying disease and reversal of advanced structural changes have not yet been achieved with current therapy, quality of life and survival have improved significantly. Targeted pulmonary vasodilator therapies, including endothelin receptor antagonists, prostacyclin analogs, and phosphodiesterase type 5 inhibitors have resulted in hemodynamic and functional improvement in children. The management of pediatric PAH remains challenging as treatment decisions depend largely on results from evidence-based adult studies and the clinical experience of pediatric experts. This article reviews the current drug therapies and their use in the management of PAH in children.

Methemoglobin and the response to inhaled nitric oxide in persistent pulmonary hypertension of the newborn

BACKGROUND

We aimed to investigate whether the change in methemoglobin levels (ΔMHb) predicts oxygenation response to inhaled nitric oxide (iNO) in persistent pulmonary hypertension of the newborn (PPHN) with lung disease, with or without pulmonary hypoplasia.

METHODS

In this prospective observational study, infants were categorized based on ΔMHb and oxygenation response (ΔPaO2/FiO2) following iNO: ΔMHb ≤0 or ΔMHb>0, and ΔPaO2/FiO2 < 20 mmHg (Non-responder) or≥20 mmHg (Responder). ΔMHb levels were compared among infants with or without pulmonary hypoplasia.

RESULTS

Among infants with pulmonary hypoplasia (n = 28), ΔMHb was not associated with an oxygenation response to iNO or survival without ECMO. Among infants without hypoplasia (n = 29), subjects with ΔMHb>0 following iNO (n = 21) had a greater ΔPaO2/FiO2 (median, 64 mmHg; IQR, 127; p < 0.01) and 100% survival without extracorporeal membrane oxygenation (ECMO) when compared to infants with ΔMHb ≤0 (n = 8; median 10 mmHg; IQR, 33).

CONCLUSIONS

PPHN secondary to lung disease without hypoplasia with increased ΔMHb following iNO was associated with better oxygenation response and survival without ECMO compared to subjects without an increase in MHb.

Inhaled nitric oxide use in neonates: Balancing what is evidence-based and what is physiologically sound

Inhaled nitric oxide is a powerful therapeutic used in neonatology. Its use is evidenced-based for term and near-term infants with persistent pulmonary hypertension; however, it is frequently used off-label both in term and preterm babies. This article reviews the off-label uses of iNO in infants. Rationale is discussed for a selective application of iNO based on physiologically guided principles, and new research avenues are considered.

Effect of NO inhalation on ECMO use rate and mortality in infants born at or near term with respiratory failure

BACKGROUND

The molecular studies showed that Nitric oxide (NO) is an essential factor which regulates pulmonary artery tension. However, the conclusions of existing clinical studies were inconsistent.

OBJECTIVE

This meta-analysis is aimed to determine whether the inhalation of NO could improve oxygenation and reduce rate of death and use of extracorporeal membrane oxygenation (ECMO).

METHODS

The strategies used to search PubMed, The Cochrane Central Register of Controlled trials in the Cochrane Library, Embase, Web of science, Clinical Trials Registry, and China Biology Medicine disc, from inception to February, 2018. The primary outcomes were death or use of ECMO, death before hospital discharge, use of ECMO before hospital discharge, change in PaO2 after treatment. We assess the risk of bias in each included study by Cochrane Handbook, and calculated typical estimates of RR, each with its 95% CI, and for continuous outcomes, WMD or a summary estimate for SMD, each with its 95% CI.

RESULTS

Nine randomized controlled trials (RCTs) with a total of 856 participants were included in this meta-analysis. This meta-analysis revealed that the experimental group had significantly lower death or use of ECMO (RR 0.66, 95% CI 0.57-0.77, I = 0%, P < .00001) and lower use of ECMO before hospital discharge (RR 0.89, 95% CI 0.50-0.71, I = 0%, P < .00001) compared to control group. And in the infants without diaphragmatic hernia, experimental group had significantly higher change in PaO2 after treatment (MD 50.40, 95% CI 32.14-68.66, P < .00001). The meta-analysis also showing a tendency to improve in the death before hospital discharge (RR 0.89, 95% CI 0.60-1.31, I = 0%, P = .55) and the change in PaO2 after treatment of the infants with diaphragmatic hernia (MD 6.70, 95% CI -2.32 to 15.72, P < .00001, P = .15), but no difference between experimental group and control group.

CONCLUSION

We found that NO inhalation can improve oxygenation and reduce rate of death and use of ECMO in this meta-analysis. Therefore, we recommend the use of NO inhalation for infants born at or near term with respiratory failure.

Association between oxygenation and ventilation indices with the time on invasive mechanical ventilation in infants

BACKGROUND

Invasive mechanical ventilation (IMV) is a common practice in pediatric intensive care unit (PICU). However, the role of oxygenation (OI) and ventilation (VI) indices regarding the time on IMV has not been fully understood.

BASIC PROCEDURES

The study was conducted with infants up to 24 months of age, hospitalized in PICU for two consecutive years. The values of ventilatory parameters, OI, VI, and blood gas of infants, collected in the first seven days in IMV, were associated with the time on IMV. IMV was classified into: short (≤seven days) and long time (>seven days). The comparison was made from the first to the seventh day. Alpha=0.05.

MAIN FINDINGS

Of 142 infants [mean age=7.51±6.33 months], 59 (41.5%) remained on IMV for a short time and 83 (58.5%) for a long time. Differences in PaO2 values were found on the second day, and PaO2/FiO2 ratio on the second, third and fourth days, with higher values in the short-term IMV. For FiO2 from the second to the fifth day; Pinsp from the first to the seventh day; PEEP from the second to the sixth day; mechanical respiratory frequency from the second to the seventh day, PaCO2 on the second day; Paw from the first to the seventh day, OI from the second to the sixth day, and VI from the first to the seventh day, the values were higher in the long-term IMV.

CONCLUSIONS

The OI and VI can be considered as potential predictors of long-term IMV, along with other markers obtained during the IMV.

Sildenafil for pulmonary hypertension in neonates

BACKGROUND

Persistent pulmonary hypertension in the neonate (PPHN) is associated with high mortality. Currently, the therapeutic mainstay for PPHN consists of assisted ventilation and administration of inhaled nitric oxide (iNO). However, nitric oxide is costly, and its use may not be appropriate in resource-poor settings. Approximately 30% of patients fail to respond to iNO. High concentrations of phosphodiesterases in the pulmonary vasculature have led to the use of phosphodiesterase inhibitors such as sildenafil or milrinone.

OBJECTIVES

To assess the efficacy and safety of sildenafil for treatment of pulmonary hypertension in neonates.

SEARCH METHODS

We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials (CENTRAL; 2017, Issue 3), MEDLINE via PubMed (1966 to 18 April 2017), Embase (1980 to 18 April 2017), and the Cumulative Index to Nursing and Allied Health Literature (CINAHL; 1982 to 18 April 2017). We searched clinical trials databases, conference proceedings, and reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.

SELECTION CRITERIA

We included randomised and quasi-randomised controlled trials of sildenafil compared with placebo or other pulmonary vasodilators, irrespective of dose, route, and duration of administration, in neonates with pulmonary hypertension, if investigators reported any of the prespecified outcomes.

DATA COLLECTION AND ANALYSIS

We assessed the methodological quality of trials regarding how bias was minimised at study entry, during study intervention, and at outcomes measurement. We extracted data on relevant outcomes; we estimated the effect size and reported it as risk ratio (RR), risk difference (RD), or mean difference (MD), as appropriate. We applied the I² test of heterogeneity and used GRADE to assess the quality of evidence.

MAIN RESULTS

For this update, we identified two additional studies, for a total of five eligible trials that enrolled 166 infants. The methodological quality of these studies ranged from low to high risk of bias. Three studies were performed in resource-limited settings, where iNO and high-frequency ventilation were not available at the time of the study. One study compared sildenafil versus active controls, and another study evaluated sildenafil as adjuvant therapy to iNO. When comparing sildenafil with placebo, investigators noted significant reduction in mortality in the sildenafil alone group (three studies, 77 participants; typical RR 0.20, 95% confidence interval (CI) 0.07 to 0.56; I² = 0% - none; typical RR -0.36, 95% CI -0.53 to -0.18; number needed to treat for an additional beneficial outcome 3, 95% CI 2 to 6; I² = 39% - low). Trials reported no significant differences in mortality upon comparison of the sildenafil group versus the active control group (one study, 65 participants; typical RR 0.55, 95% CI 0.05 to 5.75), or when iNO was administered to both groups (one study, 24 participants; typical RR 1.27, 95% CI 0.26 to 6.28). Physiological parameters of oxygenation (oxygenation index, partial pressure of oxygen in arterial blood (PaO₂)) suggested steady improvement after the first dose of sildenafil. None of the included trials identified any clinically important side effects. We rated the quality of evidence as low to very low owing to imprecision related to small sample size and unclear methodological features.

AUTHORS' CONCLUSIONS

Sildenafil used for treatment of pulmonary hypertension has potential for reducing mortality and improving oxygenation in neonates, especially in resource-limited settings where iNO is not available. However, large-scale randomised trials comparing sildenafil versus active controls (other pulmonary vasodilators) and providing follow-up for survivors are needed to assess the comparative effectiveness and long-term safety of sildenafil versus other pulmonary vasodilators.

Nitric oxide charged catheters as a potential strategy for prevention of hospital acquired infections

BACKGROUND

Catheter-Associated Hospital-Acquired Infections (HAI's) are caused by biofilm-forming bacteria. Using a novel approach, we generated anti-infective barrier on catheters by charging them with Nitric Oxide (NO), a naturally-produced gas molecule. NO is slowly released from the catheter upon contact with physiological fluids, and prevents bacterial colonization and biofilm formation onto catheter surfaces.

AIMS AND METHODS

The aim of the study was to assess the anti-infective properties of NO-charged catheters exposed to low concentration (up to 103 CFU/ml) of microbial cells in-vitro. We assessed NO-charged tracheal tubes using Pseudomonas aeruginosa, dialysis and biliary catheters using Escherichia coli, and urinary catheters using E. coli, Candida albicans or Enterococcus faecalis. Safety and tolerability of NO-charged urinary catheters were evaluated in a phase 1 clinical study in 12 patients. Six patients were catheterized with NO-charged catheters (NO-group), followed by 6 patients catheterized with regular control catheters (CT-group). Comparison of safety parameters between the study groups was performed.

RESULTS

NO-charged tracheal, dialysis biliary and urinary catheters prevented P. aeruginosa, E. coli and C. albicans attachment and colonization onto their surfaces and eradicated corresponding planktonic microbial cells in the surrounding media after 24-48 hours, while E. faecalis colonization onto urinary catheters was reduced by 1 log compared to controls. All patients catheterized with an NO-charged urinary catheter successfully completed the study without experiencing NO-related AE's or serious AE's (SAE's).

CONCLUSION

These data highlight the potential of NO-based technology as potential platform for preventing catheter-associated HAI's.

Nitric oxide for respiratory failure in infants born at or near term

BACKGROUND

Nitric oxide (NO) is a major endogenous regulator of vascular tone. Inhaled nitric oxide (iNO) gas has been investigated as treatment for persistent pulmonary hypertension of the newborn.

OBJECTIVES

To determine whether treatment of hypoxaemic term and near-term newborn infants with iNO improves oxygenation and reduces rate of death and use of extracorporeal membrane oxygenation (ECMO), or affects long-term neurodevelopmental outcomes.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review Group to search the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 1), MEDLINE via PubMed (1966 to January 2016), Embase (1980 to January 2016) and the Cumulative Index to Nursing and Allied Health Literature (CINAHL; 1982 to January 2016). We searched clinical trials databases, conference proceedings and reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials. We contacted the principal investigators of studies published as abstracts to ascertain the necessary information.

SELECTION CRITERIA

Randomised studies of iNO in term and near-term infants with hypoxic respiratory failure, with clinically relevant outcomes, including death, use of ECMO and oxygenation.

DATA COLLECTION AND ANALYSIS

We analysed trial reports to assess methodological quality using the criteria of the Cochrane Neonatal Review Group. We tabulated mortality, oxygenation, short-term clinical outcomes (particularly use of ECMO) and long-term developmental outcomes.

STATISTICS

For categorical outcomes, we calculated typical estimates for risk ratios and risk differences. For continuous variables, we calculated typical estimates for weighted mean differences. We used 95% confidence intervals and assumed a fixed-effect model for meta-analysis.

MAIN RESULTS

We found 17 eligible randomised controlled studies that included term and near-term infants with hypoxia.Ten trials compared iNO versus control (placebo or standard care without iNO) in infants with moderate or severe severity of illness scores (Ninos 1996; Roberts 1996; Wessel 1996; Davidson 1997; Ninos 1997; Mercier 1998; Christou 2000; Clark 2000; INNOVO 2007; Liu 2008). Mercier 1998 compared iNO versus control but allowed back-up treatment with iNO for infants who continued to satisfy the same criteria for severity of illness after two hours. This trial enrolled both preterm and term infants but reported most results separately for the two groups. Ninos 1997 studied only infants with congenital diaphragmatic hernia.One trial compared iNO versus high-frequency ventilation (Kinsella 1997).Six trials enrolled infants with moderate severity of illness scores (oxygenation index (OI) or alveolar-arterial oxygen difference (A-aDO2)) and randomised them to immediate iNO treatment or iNO treatment only after deterioration to more severe criteria (Barefield 1996; Day 1996; Sadiq 1998; Cornfield 1999; Konduri 2004; Gonzalez 2010).Inhaled nitric oxide appears to have improved outcomes in hypoxaemic term and near-term infants by reducing the incidence of the combined endpoint of death or use of ECMO (high-quality evidence). This reduction was due to a reduction in use of ECMO (with number needed to treat for an additional beneficial outcome (NNTB) of 5.3); mortality was not affected. Oxygenation was improved in approximately 50% of infants receiving iNO. The OI was decreased by a (weighted) mean of 15.1 within 30 to 60 minutes after the start of therapy, and partial pressure of arterial oxygen (PaO2) was increased by a mean of 53 mmHg. Whether infants had clear echocardiographic evidence of persistent pulmonary hypertension of the newborn (PPHN) did not appear to affect response to iNO. Outcomes of infants with diaphragmatic hernia were not improved; outcomes were slightly, but not significantly, worse with iNO (moderate-quality evidence).Infants who received iNO at less severe criteria did not have better clinical outcomes than those who were enrolled but received treatment only if their condition deteriorated. Fewer of the babies who received iNO early satisfied late treatment criteria, showing that earlier iNO reduced progression of the disease but did not further decrease mortality nor the need for ECMO (moderate-quality evidence). Incidence of disability, incidence of deafness and infant development scores were all similar between tested survivors who received iNO and those who did not.

AUTHORS' CONCLUSIONS

Inhaled nitric oxide is effective at an initial concentration of 20 ppm for term and near-term infants with hypoxic respiratory failure who do not have a diaphragmatic hernia.

Acute Neonatal Respiratory Failure

Acute respiratory failure requiring assisted ventilation is one of the most common reasons for admission to the neonatal intensive care unit. Respiratory failure is the inability to maintain either normal delivery of oxygen to the tissues or normal removal of carbon dioxide from the tissues. It occurs when there is an imbalance between the respiratory workload and ventilatory strength and endurance. Definitions are somewhat arbitrary but suggested laboratory criteria for respiratory failure include two or more of the following: PaCO₂ > 60 mmHg, PaO₂ < 50 mmHg or O₂ saturation <80 % with an FiO₂ of 1.0 and pH < 7.25 (Wen et al. 2004).

Initial oxygenation response to inhaled nitric oxide predicts improved outcome in congenital diaphragmatic hernia

BACKGROUND

Pulmonary hypertension (PH) is the most important complication of congenital diaphragmatic hernia (CDH) and still has a high mortality rate. The aim of this study was to evaluate the effectiveness of inhaled nitric oxide therapy in PH due to CDH.

METHODS

Hospital records of children who had undergone inhaled nitric oxide therapy for PH due to CDH between June 2009 and December 2011 were reviewed.

RESULTS

Twenty-nine patients had a diagnosis of CDH at the time of study, and eight of these patients underwent nitric oxide therapy because of failure of conventional ventilation techniques, which was successful in five of these patients. Patients who had a good overall outcome of nitric oxide therapy experienced rapid improvement (pretreatment, mean PaO2 = 44.8 mmHg; after the first hour of therapy, mean PaO2 = 96.8 mmHg), whereas patients with no response did not have a similar course (pretreatment, PaO2 = 37 mmHg; after the first hour, PaO2 = 54.6 mmHg).

CONCLUSION

Inhaled nitric oxide therapy seems to increase survival in PH due to CDH. No predictive parameters to orient patient selection could be identified; however, the early response seemed to predict the overall outcome. Good results in our series were attributed to routine use of sildenafil and dopamine, along with the nitric oxide inhalation.

Impact of early surfactant and inhaled nitric oxide therapies on outcomes in term/late preterm neonates with moderate hypoxic respiratory failure

OBJECTIVE

We conducted a post-hoc analysis of early inhaled nitric oxide (iNO)-randomized controlled trial data to identify associations pertinent to the management of moderate hypoxic respiratory failure in term/late preterm infants.

STUDY DESIGN

Univariate and multivariate logistic regression analyses were used to determine risk factors for the progression of respiratory failure and extracorporeal membrane oxygenation (ECMO)/death.

RESULT

Among the 299 enrolled infants, oxygenation index (OI) <20 at enrollment (odds ratio 0.52, confidence interval (CI) 0.27 to 0.97) and surfactant use before randomization (odds ratio 0.47, CI 0.24 to 0.91) were associated with decreased ECMO/death rates. Early surfactant use for respiratory distress syndrome, perinatal aspiration syndrome and pneumonia/sepsis was associated with lower risk of ECMO/death (P<0.001). Early iNO (OI 15 to 25) decreased the progression of respiratory failure to OI >30 (P=0.002) and to composite outcome of OI >30 or ECMO/death (P=0.02).

CONCLUSION

This post-hoc analysis suggests that early use of surfactant and iNO in moderate respiratory failure is associated with improved outcomes.

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.

Hydralazine in infants with persistent hypoxemic respiratory failure

BACKGROUND

Most deaths of infants with chronic lung disease (CLD) are caused by respiratory failure, unremitting pulmonary artery hypertension (PAH) with cor pulmonale, or infection. Although the exact prevalence of PAH in infants with CLD is unknown, infants with CLD and severe PAH have a high mortality rate. Except for oxygen supplementation, no specific interventions have been established as effective in the treatment for PAH in premature infants with CLD. Little has been proven regarding the clinical efficacy of vasodilators and concerns remain regarding adverse effects.

OBJECTIVES

To review current evidence for the benefits and harms of hydralazine therapy to infants with persistent hypoxemic respiratory failure.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), MEDLINE via PubMed and EMBASE, and other clinical trials registries through November 2011 using the standard search strategy of the Cochrane Neonatal Review Group. We searched these databases using a strategy combining a variation of the Cochrane highly sensitive search strategy for identifying randomised trials in MEDLINE; sensitivity-maximising version with selected MeSH and free-text terms: hydralazine, vasodilator agent, antihypertensive agent, heart diseases, lung diseases, respiratory tract diseases, infant, and randomised controlled trial.

SELECTION CRITERIA

We considered only randomised controlled trials and quasi-randomised trials for inclusion. We included low birth weight (LBW) infants with persistent hypoxemic respiratory failure who were treated with any type of hydralazine therapy.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality according to pre-specified criteria.

MAIN RESULTS

We found no studies meeting the criteria for inclusion in this review.

AUTHORS' CONCLUSIONS

There was insufficient evidence to determine the safety and efficacy of hydralazine in LBW infants with persistent hypoxemic respiratory failure. Since hydralazine is inexpensive and potentially beneficial, randomised controlled trials are recommended. Such trials are particularly needed in settings where other medications such as sildenafil, inhaled nitric oxide (iNO), or extracorporeal membrane oxygenation (ECMO) are not available.

Oxidative stress and persistent pulmonary hypertension of the newborn treated with inhaled nitric oxide and different oxygen concentrations

OBJECTIVES

The aim of this study was to determine the effects of inhaled NO with different oxygen concentrations on the inflammatory cascade in newborns with hypoxic respiratory failure secondary to persistent pulmonary hypertension.

METHODS

60 newborns received iNO and 30 of them received an initial oxygen concentration of 45% (group 1), while the other 30 newborns received an initial oxygen concentration of 80% (group 2). The levels of inflammatory cytokines (IL-6, IL-8, TNF-α) were measured. The clinical outcome was also recorded.

RESULTS

The findings show that interleukin concentrations (IL-6, IL-8, TNF-α) were significantly decreased between 0 and 72 hours (p < 0.01) in the newborns exposed to initial oxygen concentration of 45% and significantly increased in the other group.

CONCLUSIONS

When inhaled, NO was co-administered with concentration of O(2) <45%, anti-inflammatory responses occurred, in accord with evidence in the published literature. The benefits of iNO on the clinical outcome in the current study demonstrate that inhaled NO in both groups was associated with improved short-term oxygenation.

Respiratory support in meconium aspiration syndrome: a practical guide

Meconium aspiration syndrome (MAS) is a complex respiratory disease of the term and near-term neonate. Inhalation of meconium causes airway obstruction, atelectasis, epithelial injury, surfactant inhibition, and pulmonary hypertension, the chief clinical manifestations of which are hypoxaemia and poor lung compliance. Supplemental oxygen is the mainstay of therapy for MAS, with around one-third of infants requiring intubation and mechanical ventilation. For those ventilated, high ventilator pressures, as well as a relatively long inspiratory time and slow ventilator rate, may be necessary to achieve adequate oxygenation. High-frequency ventilation may offer a benefit in infants with refractory hypoxaemia and/or gas trapping. Inhaled nitric oxide is effective in those with pulmonary hypertension, and other adjunctive therapies, including surfactant administration and lung lavage, should be considered in selected cases. With judicious use of available modes of ventilation and adjunctive therapies, infants with even the most severe MAS can usually be supported through the disease, with an acceptably low risk of short- and long-term morbidities.

Advances in the management of meconium aspiration syndrome

Meconium aspiration syndrome (MAS) is a common cause of severe respiratory distress in term infants, with an associated highly variable morbidity and mortality. MAS results from aspiration of meconium during intrauterine gasping or during the first few breaths. The pathophysiology of MAS is multifactorial and includes acute airway obstruction, surfactant dysfunction or inactivation, chemical pneumonitis with release of vasoconstrictive and inflammatory mediators, and persistent pulmonary hypertension of newborn (PPHN). This disorder can be life threatening, often complicated by respiratory failure, pulmonary air leaks, and PPHN. Approaches to the prevention of MAS have changed over time with collaboration between obstetricians and pediatricians forming the foundations for care. The use of surfactant and inhaled nitric oxide (iNO) has led to the decreased mortality and the need for extracorporeal membrane oxygenation (ECMO) use. In this paper, we review the current understanding of the pathophysiology and management of MAS.

Júnior AA, Grande RA, Ribeiro MÂGO, Ribeiro JD. Relação entre índice de oxigenação e ventilação com o tempo em ventilação mecânica de pacientes em terapia intensiva pediátrica

OBJETIVO: Correlacionar o índice de oxigenação (IO) e o de ventilação (IV) com o tempo de ventilação mecânica invasiva (VMI) em pacientes pediátricos. MÉTODOS: Estudo prospectivo, observacional, com pacientes de 28 dias de vida a 14 anos de idade, internados na Unidade de Terapia Intensiva Pediátrica de um hospital universitário. Correlacionaram-se valores de idade, peso, pH, pressão parcial de oxigênio (PaO2), pressão parcial de gás carbônico (PaCO2), IO e IV, nos primeiros cinco dias em VMI, com o tempo em que o paciente permaneceu em VMI. O tempo total de ventilação mecânica foi dividido em <7 dias e >7 dias. RESULTADOS: Foram estudados 28 pacientes. Houve correlação negativa significante do tempo de VMI com o pH no quarto dia e com a PaO2 no quinto dia. Houve correlação positiva com o IO no terceiro e quarto dias e com o IV no terceiro, quarto e quinto dias. Houve diferença na idade e pH no quarto e quinto dias e IV do segundo ao quinto dias entre o grupo que permaneceu menos de sete dias e o que permaneceu sete dias ou mais em VMI. CONCLUSÕES: IO, IV, pH e PaO2, medidos precocemente, associaram-se com VMI prolongada, refletindo a gravidade do distúrbio ventilatório inicial.

Sildenafil for pulmonary hypertension in neonates

BACKGROUND

Persistent pulmonary hypertension in neonates (PPHN) is associated with high mortality. Currently, the therapeutic mainstay for PPHN is assisted ventilation and administration of inhaled nitric oxide (iNO). However, nitric oxide is costly and may not be appropriate in resource-poor settings. Approximately 30% of patients fail to respond to iNO. High concentrations of phosphodiesterases in the pulmonary vasculature has led to the use of phosphodiesterase inhibitors such as sildenafil or milrinone.

OBJECTIVES

To assess the efficacy and safety of sildenafil in the treatment of persistent pulmonary hypertension in neonates.

SEARCH STRATEGY

The Cochrane Central Register of Controlled Trials (The Cochrane Library), MEDLINE, EMBASE, CINAHL databases were searched from their inception until December 2010; Clinicaltrials.gov web site, the reference lists of identified trials, and abstracts of meetings were searched without any language restriction.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials of sildenafil compared with placebo or other pulmonary vasodilators, irrespective of dose, route and duration of administration in neonates with PPHN, were included if the trial reported any of the pre-specified outcomes.

DATA COLLECTION AND ANALYSIS

The methodological quality of the trials was assessed regarding how bias was minimized at study entry, during study intervention and at outcomes measurement. Data on relevant outcomes were extracted and the effect size was estimated and reported as relative risk (RR), risk difference (RD) and weighted mean difference (MD) as appropriate. The I-squared (I(2)) test of heterogeneity was applied.

MAIN RESULTS

Three eligible trials that enrolled 77 infants were identified. The methodological quality of the studies indicated low-moderate risk of bias. All studies were performed in resource-limited settings where iNO and high frequency ventilation were not available at the time of study. There was significant reduction in mortality in the sildenafil group (typical RR 0.20, 95% CI 0.07 to 0.57; typical RD -0.38, 95% CI -0.60 to -0.16; Number needed to treat to benefit 3, 95% CI 2 to 6). Physiological parameters of oxygenation (oxygenation index, PaO(2)) suggested a steady improvement after the first dose of sildenafil. No clinically important side effects were identified.

AUTHORS' CONCLUSIONS

Sildenafil in the treatment of PPHN has significant potential especially in resource limited settings. However, a large scale randomised trial comparing sildenafil with the currently used vasodilator, inhaled nitric oxide, is needed to assess efficacy and safety.

Can we improve outcome of congenital diaphragmatic hernia?

This review gives an overview of the disease spectrum of congenital diaphragmatic hernia (CDH). Etiological factors, prenatal predictors of survival, new treatment strategies and long-term morbidity are described. Early recognition of problems and improvement of treatment strategies in CDH patients may increase survival and prevent secondary morbidity. Multidisciplinary healthcare is necessary to improve healthcare for CDH patients. Absence of international therapy guidelines, lack of evidence of many therapeutic modalities and the relative low number of CDH patients calls for cooperation between centers with an expertise in the treatment of CDH patients. The international CDH Euro-Consortium is an example of such a collaborative network, which enhances exchange of knowledge, future research and development of treatment protocols.

Advances in the diagnosis and management of persistent pulmonary hypertension of the newborn

Rapid evaluation of a neonate who is cyanotic and in respiratory distress is essential for achieving a good outcome. Persistent pulmonary hypertension of the newborn (PPHN) can be a primary cause or a contributing factor to respiratory failure, particularly in neonates born at 34 weeks or more of gestation. PPHN represents a failure of normal postnatal adaptation that occurs at birth in the pulmonary circulation. Rapid advances in therapy in recent years have led to a remarkable decrease in mortality for the affected infants. Infants who survive PPHN are at significant risk for long-term hearing and neurodevelopmental impairments, however. This review focuses on the diagnosis, recent advances in management, and recommendations for the long-term follow-up of infants who have PPHN.

Inhaled nitric oxide in the neonate

Inhaled nitric oxide (iNO) has been used to treat both term and preterm infants with respiratory failure. Term infants with persistent pulmonary hypertension, either as a primary cause or secondary to other disease processes, respond to iNO with improvement in oxygenation indices and a decreased need for extracorporeal membrane oxygenation. Infants with congenital diaphragmatic hernia are the exception to this finding, with little clinical benefit observed with iNO treatment. Although respiratory disease in preterm infants has a component of increased pulmonary vascular resistance, little benefit of iNO administration has been observed in premature infants either early in their course or later as a treatment to prevent the evolution of chronic lung disease.

Nitric oxide administration using an oxygen hood: a pilot trial

BACKGROUND

We have shown earlier that inhaled nitric oxide (iNO) administered by oxygen hood reduces pulmonary hypertension in an animal model (J Perinatol 2002; 22:50-6). Our objective in this study was to determine feasibility of iNO by oxygen hood in neonates with elevated alveolar-arterial oxygen gradients (A-aDO(2)).

METHODS/PRINCIPAL FINDINGS

Masked randomized controlled pilot trial. Inclusion criteria were: gestation>or=34 weeks, age<7 days, with post-ductal arterial line, and A-aDO(2) 400-600. Infants were randomized to study gas (iNO 20 ppm or equivalent O(2) flow) for 1 hr which was then weaned over the next 4 hours. Primary outcome was PaO(2) one hour post-randomization. Four infants each were randomized to iNO or O(2) (controls). Two of the four infants given iNO had an increase in PaO(2) of >100 torr, while oxygenation was unchanged in the controls. Methemoglobinemia and other adverse effects were not noted in any infant. Environmental levels of NO and NO(2) were minimal (<1 ppm) at >0.3 m from the hood.

CONCLUSIONS

Administration of iNO by oxygen hood is feasible. Larger randomized controlled trials are required to measure the efficacy and determine an appropriate target population for this technique.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00041548.

Inhaled nitric oxide in the term newborn

Inhaled nitric oxide is a selective pulmonary vasodilator that serves integral diagnostic and therapeutic roles in the clinical management of near-term and term newborns with hypoxemic respiratory failure and pulmonary hypertension. Its proper use and potential limitations in current clinical practice are reviewed.

Effects of hyperoxia and nitric oxide on endogenous nitric oxide production in polymorphonuclear leukocytes

BACKGROUND

Exposure to hyperoxia and nitric oxide (NO) occur frequently during the treatment of neonatal hypoxic pulmonary failure.

OBJECTIVE

The aim of the study was to quantify the endogenous synthesis of NO in neonatal polymorphonuclear neutrophils following exposure to hyperoxia and NO in vitro.

METHODS

Neonatal cord blood was exposed to room air, 25, 30 and 100% oxygen and 10 or 20 ppm NO added to the different oxygen concentrations for up to 30 min. 4,5-Diaminofluorescein diacetate (DAF-2 DA) is an intracellular dye used to measure real-time changes in NO levels in vivo. The molecular structure of DAF-2 DA changes upon contact with NO to its oxidized and fluorescent form diaminofluorescein-triazol (DAF-2T) and after being hydrolyzed by intracellular esterases cannot leave the cell. DAF-2 DA signals following equilibration with room air were used as controls.

RESULTS

Exposure to 100% oxygen increased NO production significantly when compared to 20 ppm NO plus 100% oxygen (p = 0.031) and to 20 ppm NO alone (p = 0.006). 10 ppm NO produced a similar effect. Significant increases in NO production were also noticed following exposure to 25% oxygen. This increase was already present after 10 min of oxygen exposure.

CONCLUSION

These findings support the propagated avoidance of hyperoxia not only in preterm infants, but also in term neonates.

Nitric oxide/cGMP protects endothelial cells from hypoxia-mediated leakiness

Leakiness of the endothelial bed is attributed to the over-perfusion of the pulmonary bed, which leads to high altitude pulmonary edema (HAPE). Inhalation of nitric oxide has been successfully employed to treat HAPE patients. We hypothesize that nitric oxide intervenes in the permeability of the pulmonary macrovascular endothelial bed to rectify the leaky bed under hypoxia. Our present work explores the underlying mechanism of 'hypoxia-mediated' endothelial malfunction by using human umbilical cord-derived immortalized endothelial cells, ECV-304, and bovine pulmonary artery primary endothelial cells. The leakiness of the endothelial monolayer was increased by two-fold under hypoxia in comparison to cells under normoxia, while optical tweezers-based tethering assays reported a higher membrane tension of endothelial cells under hypoxia. Phalloidin staining demonstrated depolymerization of F-actin stress fibers and highly polarized F-actin patterns in endothelial cells under hypoxia. Nitric oxide, 8-Br-cGMP and sildenafil citrate (phosphodiesterase type 5 inhibitor) led to recovery from hypoxia-induced leakiness of the endothelial monolayers. Results of the present study also suggest that 'hypoxia-induced' cytoskeletal rearrangements and membrane leakiness are associated with the low nitric oxide availability under hypoxia. We conclude that nitric oxide-based recovery of hypoxia-induced leakiness of endothelial cells is a cyclic guanosine monophosphate (cGMP)-dependent phenomenon.

Inhaled nitric oxide therapy during the transport of neonates with persistent pulmonary hypertension or severe hypoxic respiratory failure

Our aim was to determine whether starting inhaled nitric oxide (iNO) on critically ill neonates with severe hypoxemic respiratory failure and/or persistent pulmonary hypertension (PPH), at a referring hospital at the start of transport, decreases the need for extracorporeal membrane oxygenation (ECMO), lessens the number of hospital days and improves survival in comparison with those patients who were started on iNO only at the receiving facility. The study was a retrospective review of 94 charts of neonates that had iNO initiated by the transport team at a referring hospital or only at the tertiary neonatal intensive care unit (NICU) of the receiving hospital. Data collected included demographics, mode of transport, total number of hospital days, days on inhaled nitric oxide and ECMO use. Of the 94 patients, 88 were included. Of these, 60 were started on iNO at the referring facility (Field-iNO) and 28 were started at the receiving NICU (CHLA-iNO). All patients survived transport to the receiving NICU. Death rates and ECMO use were similar in both groups. Overall, patients who died were younger and had lower birth weights and Apgar scores. For all surviving patients who did not require ECMO, the length of total hospital stay (median days 22 versus 38, P = 0.018), and the length of the hospital stay at the receiving hospital (median days 18 versus 29, P = 0.006), were significantly shorter for the Field-iNO patients than for the CHLA-iNO patients, respectively. Earlier initiation of iNO may decrease length of hospital stay in surviving neonates with PPH not requiring ECMO.

Sildenafil for pulmonary hypertension in neonates

BACKGROUND

Persistent pulmonary hypertension in neonates (PPHN) is associated with high mortality. Currently, the therapeutic mainstay for PPHN is assisted ventilation and administration of inhaled nitric oxide (iNO). However, nitric oxide is costly and may not be appropriate in resource-poor settings. Approximately 30% of patients fail to respond to iNO. High concentrations of phosphodiesterases in the pulmonary vasculature has led to the use of phosphodiesterase inhibitors such as sildenafil or milrinone.

OBJECTIVES

To assess the efficacy and safety of Sildenafil in the treatment of persistent pulmonary hypertension in neonates.

SEARCH STRATEGY

MEDLINE, EMBASE, CINAHL databases were searched from their inception until March 2007; the Cochrane Central Register of Controlled Trials, the Cochrane Library, the reference lists of identified trials, and abstracts of meetings were searched without any language restriction.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of Sildenafil compared with placebo or other pulmonary vasodilators, irrespective of dose, route and duration of administration in neonates with PPHN, were included if the trial reported any of the pre-specified outcomes.

DATA COLLECTION AND ANALYSIS

The methodological quality of the trials was assessed regarding how bias at study entry, study intervention and outcomes measurement was minimized. Data on relevant outcomes were extracted and the effect size was estimated and reported as relative risk (RR), risk difference (RD) and weighted mean difference (MD) as appropriate. The I-squared (I(2)) test of heterogeneity was applied.

MAIN RESULTS

Two small eligible trials (one full article and one abstract) were identified. The methodological quality of the trial presented in the full article was good. Information provided in the abstract was limited. The total number of enrolled patients in the two studies was 37. Both studies were performed in resource-limited settings where iNO and high frequency ventilation are not available. Both studies reported statistically significant improvement in oxygenation (reduction in oxygenation index) in the Sildenafil group. One study reported what would be, if replicated, a strongly protective effect on mortality (RR 0.17, 95% CI 0.03, 1.09) favoring the Sildenafil group. However, this result needs to be replicated in larger studies. No clinically important side effects were reported.

AUTHORS' CONCLUSIONS

The safety and effectiveness of sildenafil in the treatment of PPHN has not yet been established and its use should be restricted within the context of randomized controlled trials. Further randomized controlled trials of adequate power comparing Sildenafil with other pulmonary vasodilators are needed in moderately ill infants with PPHN.

Nitric oxide for respiratory failure in infants born at or near term

BACKGROUND

Nitric oxide is a major endogenous regulator of vascular tone. Inhaled nitric oxide gas has been investigated as a treatment for persistent pulmonary hypertension of the newborn.

OBJECTIVES

To determine whether treatment of hypoxaemic term and near-term newborn infants with inhaled nitric oxide (iNO) improves oxygenation and reduces the rates of death, the requirement for extracorporeal membrane oxygenation (ECMO), or affects long term neurodevelopmental outcomes.

SEARCH STRATEGY

Electronic and hand searching of pediatric/neonatal literature and personal data files. In addition we contacted the principal investigators of articles which have been published as abstracts to ascertain the necessary information.

SELECTION CRITERIA

Randomized and quasi-randomized studies of inhaled nitric oxide in term and near term infants with hypoxic respiratory failure. Clinically relevant outcomes, including death, requirement for ECMO, and oxygenation.

DATA COLLECTION AND ANALYSIS

Trial reports were analysed for methodologic quality using the criteria of the Cochrane Neonatal Review Group. Results of mortality, oxygenation, short term clinical outcomes (particularly need for ECMO), and long term developmental outcomes were tabulated.

STATISTICS

For categorical outcomes, typical estimates for relative risk and risk difference were calculated. For continuous variables, typical estimates for weighted mean difference were calculated. 95% confidence intervals were used. A fixed effect model was assumed for meta-analysis.

MAIN RESULTS

Fourteen eligible randomized controlled studies were found in term and near term infants with hypoxia. Seven of the trials compared iNO to control (placebo or standard care without iNO) in infants with moderate or severe severity of illness scores. Four of the trials compared iNO to control, but allowed back up treatment with iNO if the infants continued to satisfy the same criteria for severity of illness after a defined period of time. Two trials enrolled infants with moderate severity of illness score (OI or AaDO2) and randomized to immediate iNO treatment or iNO treatment only if they deteriorated to more severe criteria. One trial studied only infants with congenital diaphragmatic hernia (Ninos 1997), and one trial enrolled both preterm and term infants (Mercier 1998), but reported the majority of the results separately for the two groups. Inhaled nitric oxide appears to improve outcome in hypoxaemic term and near term infants by reducing the incidence of the combined endpoint of death or need for ECMO. The reduction seems to be entirely a reduction in need for ECMO; mortality is not reduced. Oxygenation improves in approximately 50% of infants receiving nitric oxide. The Oxygenation Index decreases by a (weighted) mean of 15.1 within 30 to 60 minutes after commencing therapy and PaO2 increases by a mean of 53 mmHg. Whether infants have clear echocardiographic evidence of persistent pulmonary hypertension of the newborn (PPHN) or not does not appear to affect outcome. The outcome of infants with diaphragmatic hernia was not improved; indeed there is a suggestion that outcome was slightly worsened. The incidence of disability, incidence of deafness and infant development scores are all similar between tested survivors who received nitric oxide or not.

AUTHORS' CONCLUSIONS

On the evidence presently available, it appears reasonable to use inhaled nitric oxide in an initial concentration of 20 ppm for term and near term infants with hypoxic respiratory failure who do not have a diaphragmatic hernia.

Contribution of pulmonary surfactant with inhaled nitric oxide for treatment of pulmonary hypertension

BACKGROUND

Combined therapy of inhaled nitric oxide (iNO) with pulmonary surfactant replacement was reported to improve oxygenation in patients or animal models of persistent pulmonary hypertension of the newborn with pulmonary surfactant deficiency lung. To evaluate the potential of iNO for the treatment of persistent pulmonary hypertension of the newborn, pulmonary arterial pressure (PAP) was measured during iNO before and after pulmonary surfactant replacement in an animal model of pulmonary hypertension with surfactant deficiency.

METHODS

Seven newborn piglets were injected with L-nitro-arginine-methylester to produce an animal model of pulmonary hypertension. After PAP increased, iNO (30 p.p.m.) was introduced. Then iNO was stopped, and animals were subjected to lung lavage with saline. After recording the effect of iNO, all animals then received exogenous pulmonary surfactant installation. After surfactant treatment, iNO was again introduced.

RESULTS

Pulmonary arterial pressure and systemic arterial pressure were increased significantly by >30% after infusion of L-nitro-arginine-methylester. During iNO only PAP was reduced significantly. Respiratory system compliance decreased significantly after lung lavage, and increased significantly after pulmonary surfactant replacement with concomitant increase of PaO2. In contrast, significant reduction of PAP with iNO before and after pulmonary surfactant replacement were also observed. The reduction ratios of PAP under each condition were 75.2 +/- 7.4%, 81.3 +/- 3.1%, and 79.1 +/- 5.3%, respectively (not significant among conditions).

CONCLUSION

These results suggest that iNO is still a potent pulmonary arterial vasodilator even under pulmonary surfactant deficiency in an animal model of pulmonary hypertension.

Pulmonary nitric oxide synthases and nitrotyrosine: findings during lung development and in chronic lung disease of prematurity

BACKGROUND

Nitric oxide mediates and modulates pulmonary transition from fetal to postnatal life. NO is synthesized by 3 nitric oxide synthase isoforms. One key pathway of nitric oxide metabolism results in nitrotyrosine, a stable, measurable marker of nitric oxide production.

OBJECTIVE

The purpose of this study was to assess, by semiquantitative immunohistochemistry, nitric oxide synthase isoforms and nitrotyrosine at different airway and vascular tree levels in the lungs of neonates at different gestational ages and to compare results in control groups to those in infants with chronic lung disease.

DESIGN/METHODS

Formalin-fixed, paraffin-embedded, postmortem lung blocks were prepared for immunohistochemistry using antibodies to each nitric oxide synthase isoform and to nitrotyrosine. Blinded observers evaluated the airway and vascular trees for staining intensity (0-3 scale) at 5 levels and 3 levels, respectively. The control population consisted of infants from 22 to 42 weeks' gestation who died in < 48 hours. Results were compared with gestation-matched infants with varying severity of chronic lung disease.

RESULTS

In control and chronic lung disease groups, 22 to 42 weeks' gestation, staining for all 3 of the nitric oxide synthase isoforms was found in the airway epithelium from the bronchus to the alveolus or distal-most airspace. The abundance or distribution of nitric oxide synthase-3 staining in the airways did not show significant correlation with gestational age or severity of chronic lung disease. In the vascular tree, intense nitric oxide synthase-3 and moderate nitric oxide synthase-2 staining was found; nitric oxide synthase-1 was not consistently stained. Nitrotyrosine did stain in the pulmonary tree. Compared with controls where nitrotyrosine staining was minimal, regardless of gestation, in infants with chronic lung disease there was more than fourfold increase between severe chronic lung disease (n = 12) and either mild chronic lung disease or control infants (n = 16).

CONCLUSIONS

All 3 of the nitric oxide synthase isoforms and nitrotyrosine are detectable by immunohistochemistry early in lung development. Nitric oxide synthase ontogeny shows no significant changes in abundance or distribution with advancing gestational age nor with chronic lung disease. Nitrotyrosine is significantly increased in severe chronic lung disease.

Carbon monoxide reverses established pulmonary hypertension

Pulmonary arterial hypertension (PAH) is an incurable disease characterized by a progressive increase in pulmonary vascular resistance leading to right heart failure. Carbon monoxide (CO) has emerged as a potently protective, homeostatic molecule that prevents the development of vascular disorders when administered prophylactically. The data presented in this paper demonstrate that CO can also act as a therapeutic (i.e., where exposure to CO is initiated after pathology is established). In three rodent models of PAH, a 1 hour/day exposure to CO reverses established PAH and right ventricular hypertrophy, restoring right ventricular and pulmonary arterial pressures, as well as the pulmonary vascular architecture, to near normal. The ability of CO to reverse PAH requires functional endothelial nitric oxide synthase (eNOS/NOS3) and NO generation, as indicated by the inability of CO to reverse chronic hypoxia-induced PAH in eNOS-deficient (nos3^−/−) mice versus wild-type mice. The restorative function of CO was associated with a simultaneous increase in apoptosis and decrease in cellular proliferation of vascular smooth muscle cells, which was regulated in part by the endothelial cells in the hypertrophied vessels. In conclusion, these data demonstrate that CO reverses established PAH dependent on NO generation supporting the use of CO clinically to treat pulmonary hypertension.

A novel inhaled organic nitrate that affects pulmonary vascular tone in a piglet model of hypoxia-induced pulmonary hypertension

Persistent pulmonary hypertension of the newborn is characterized by elevated pulmonary vascular resistance after birth leading to right-to-left shunting and systemic arterial hypoxemia. Inhaled nitric oxide (NO) is effective in reducing the need for extracorporeal membrane oxygenation, but it has potential toxicities, especially in an oxygen-rich environment. A number of other NO-based molecules have been given by inhalation, but their structure-function relationships have not been established. Recent studies have raised the idea that toxic and beneficial properties can be separated. We synthesized a novel organic nitrate [ethyl nitrate (ENO2)], tested it in vitro, and administered it to hypoxic piglets. ENO2 lowered pulmonary artery pressure and raised the Po2 in arterial blood but did not alter systemic vascular resistance or methemoglobin levels. In addition, we tested the effect of ENO2 in the presence of the thiol glutathione, both in vivo and in vitro, and found its action to be enhanced. Although ENO2 is less potent than inhaled NO on a dose-equivalency basis, pretreatment of hypoxic animals with glutathione, which may be depleted in injured lungs, led to a markedly enhanced effect (largely mitigating the difference in potency). These results suggest that ENO2 may hold promise as a safe alternative to NO, particularly in hypoxemic conditions characterized by thiol depletion.

Extracorporeal membrane oxygenation in infants with meconium aspiration syndrome: a decade of experience with venovenous ECMO

BACKGROUND

Despite the emergence of new therapies for respiratory failure of the newborn with meconium aspiration syndrome (MAS), extracorporeal membrane oxygenation (ECMO) has a significant role as a rescue modality in these infants. Our objective was to compare the use of venovenous (VV) vs venoarterial (VA) ECMO in newborns with MAS who need ECMO and to ascertain the impact of new therapies in these infants during the last decade. We also evaluated how disease severity or time of ECMO initiation affected mortality and morbidity.

METHODS

A report of 12 years experience (1990-2002) of a single center, comparing VV and VA ECMO, is given. Venovenous ECMO was the preferred rescue modality for respiratory failure unresponsive to maximal medical therapy. Venoarterial ECMO was used only when the placement of a VV ECMO 14-F catheter was not possible; 128 patients met ECMO criteria, 114 were treated with VV ECMO, and 12 with VA ECMO. Two patients were converted from VV to VA ECMO.

RESULTS

Venovenous and VA ECMO patients had comparable birth weight (mean +/- SEM, 3.48 +/- 0.05 vs 3.35 +/- 0.15 kg) and gestational age (40.3 +/- 0.1 vs 40.7 +/- 0.3 weeks). Before ECMO, there was no difference between VV and VA ECMO patients in oxygenation index (60 +/- 3 vs 63 +/- 8), mean airway pressure (19.5 +/- 0.4 vs 20.8 +/- 1.5 cm H2O), alveolar-arterial O2 gradient (630 +/- 2 vs 632 +/- 4 torr), ECMO cannulation age (median [25th-75th percentiles], 23 [14-47] vs 26 [14-123] hours), or in the % of patients who needed vasopressors/inotropes (98% vs 100%). From November 1994, inhaled nitric oxide (NO) was available. Before VV ECMO, 67% of the patients received NO, 24% received surfactant, and 48% were treated with high-frequency ventilation (HFV). There was no significant difference between VV and VA ECMO patients in survival rate (94% vs 92%), ECMO duration (88 [64-116] vs 94 [55-130] hours), time of extubation (9 [7-11] vs 14 [9-15] days), age at discharge (23 [18-30] vs 27 [15-41] days), or incidence of short-term intracranial complications (5.3% vs 16.7%). For the total cohort of 126 infants, indices of disease severity (oxygenation index, alveolar-arterial O 2 gradient, mean airway pressure) did not correlate with outcome measures. Delay in ECMO initiation (> 96 hours) was associated with prolonged mechanical ventilation and hospitalization (P < .01). New therapies (NO, HFV, surfactant) in the second part of the decade were associated with a longer ECMO duration (98 [80-131] vs 87 [60-116] hours; P < .05), no delay in ECMO initiation time (23 [10-40] vs 24 [14-52] hours), and no significant change in survival (97% vs 92.5%). No patient was treated with VA ECMO after 1994.

CONCLUSIONS

Venovenous ECMO is as reliable as VA ECMO in newborns with MAS in severe respiratory failure who need ECMO. Delay in ECMO initiation may result in prolonged mechanical ventilation and increased length of hospital stay. The emergence of new conventional therapies (NO, HFV, surfactant) and particularly increased experience enable sole use of VV ECMO with no significant change in survival in infants with MAS.