Life-threatening effects of discontinuing inhaled nitric oxide in children

Compatibility and Safety Implications Associated with Interfacing Medical Devices in Neonatal Respiratory Care: A Case Example Using the Inhaled Nitric Oxide Delivery System

Over the past decade, international organizations have instituted strict regulations for the safe use of connected medical devices. The International Organization for Standardization and the Medical Device Single Audit Program instituted certifications to ensure that connected devices are compatible and operate within their proper clinical parameters. These efforts came about, in part, as a consequence of clinicians’ decisions to use nonstandard, modified, or improvised devices for purposes outside the original manufacturers’ approved parameters. Unapproved device modifications can be associated with increased risk of dosing errors, monitoring errors, tubing misconnections and serious or potentially fatal adverse events; furthermore, health care providers who implement unapproved device modifications may assume legal and financial liability should harm come to patients as a consequence of the modification. Using the inhaled nitric oxide delivery system as an example, the objective of this paper is to raise awareness of the potential dangers associated with unapproved modification and interfacing of therapeutic gas delivery systems and ventilators in the neonatal intensive care unit setting. The paper also highlights the rationale and necessity for rigorous validation processes that ensure that interfaced medical devices perform as intended in the clinical setting.

Rationale for Use of an FDA-Cleared Delivery System for Administration of Inhaled Nitric Oxide in Patients Undergoing Magnetic Resonance Imaging

Inhaled nitric oxide (iNO) is a pulmonary vasodilator approved for use to improve lung function in neonates >34 weeks' gestational age with hypoxic respiratory failure and pulmonary hypertension. Infants with severe respiratory disease frequently require magnetic resonance imaging (MRI) scans for evaluation of treatment and diagnosis of concurrent disease processes. Until 2015, incompatibility between the standard iNO delivery system components and the magnetic field within the MRI setting required iNO treatment to be interrupted for MRI, which could increase risk of deoxygenation and rebound pulmonary hypertension. In some cases, patients had to forego or delay MRI in order to maintain uninterrupted iNO delivery. The US Food and Drug Administration cleared the first iNO delivery system specifically modified for conditional use with MRI scanners (INOmax DS_IR ^® Plus MRI) in 2015, based on the determination that the MRI-cleared system met the performance standards equivalent to the standard system. The system design and manufacturer risk management activities, as well as the regulatory requirements for clearance and continued use, provide necessary safeguards to ensure that high-risk neonates receive uninterrupted iNO in a safe manner. Anecdotal reports suggest that adoption of the MRI-cleared system may help optimize care for critically ill neonates who require concurrent administration of iNO and MRI scanning. Further research will be necessary to quantify the nature and magnitude of clinical improvements associated with adoption of the MRI iNO delivery system.

Protocol of a randomised controlled trial in cardiac surgical patients with endothelial dysfunction aimed to prevent postoperative acute kidney injury by administering nitric oxide gas

INTRODUCTION

Postoperative acute kidney injury (AKI) is a common complication in cardiac surgery. Levels of intravascular haemolysis are strongly associated with postoperative AKI and with prolonged (>90 min) use of cardiopulmonary bypass (CPB). Ferrous plasma haemoglobin released into the circulation acts as a scavenger of nitric oxide (NO) produced by endothelial cells. Consequently, the vascular bioavailability of NO is reduced, leading to vasoconstriction and impaired renal function. In patients with cardiovascular risk factors, the endothelium is dysfunctional and cannot replenish the NO deficit. A previous clinical study in young cardiac surgical patients with rheumatic fever, without evidence of endothelial dysfunction, showed that supplementation of NO gas decreases AKI by converting ferrous plasma haemoglobin to ferric methaemoglobin, thus preserving vascular NO. In this current trial, we hypothesised that 24 hours administration of NO gas will reduce AKI following CPB in patients with endothelial dysfunction.

METHODS

This is a single-centre, randomised (1:1) controlled, parallel-arm superiority trial that includes patients with endothelial dysfunction, stable kidney function and who are undergoing cardiac surgery procedures with an expected CPB duration >90 min. After randomisation, 80 parts per million (ppm) NO (intervention group) or 80 ppm nitrogen (N2, control group) are added to the gas mixture. Test gases (N2 or NO) are delivered during CPB and for 24 hours after surgery. The primary study outcome is the occurrence of AKI among study groups. Key secondary outcomes include AKI severity, occurrence of renal replacement therapy, major adverse kidney events at 6 weeks after surgery and mortality. We are recruiting 250 patients, allowing detection of a 35% AKI relative risk reduction, assuming a two-sided error of 0.05.

ETHICS AND DISSEMINATION

The Partners Human Research Committee approved this trial. Recruitment began in February 2017. Dissemination plans include presentations at scientific conferences, scientific publications and advertising flyers and posters at Massachusetts General Hospital.

TRIAL REGISTRATION NUMBER

NCT02836899.

New Modalities for the Administration of Inhaled Nitric Oxide in Intensive Care Units After Cardiac Surgery or for Neonatal Indications: A Prospective Observational Study

BACKGROUND

Nitric oxide (NO) has a well-known efficacy in pulmonary hypertension (PH), with wide use for 20 years in many countries. The objective of this study was to describe the current use of NO in real life and the gap with the guidelines.

METHODS

This is a multicenter, prospective, observational study on inhaled NO administered through an integrated delivery and monitoring device and indicated for PH according to the market authorizations. The characteristics of NO therapy and ventilation modes were observed. Concomitant pulmonary vasodilator treatments, safety data, and outcome were also collected. Quantitative data are expressed as median (25th, 75th percentile).

RESULTS

Over 1 year, 236 patients were included from 14 equipped and trained centers: 117 adults and 81 children with PH associated with cardiac surgery and 38 neonates with persistent PH of the newborn. Inhaled NO was initiated before intensive care unit (ICU) admission in 57%, 12.7%, and 38.9% with an initial dose of 10 (10, 15) ppm, 20 (18, 20) ppm, and 17 (11, 20) ppm, and a median duration of administration of 3.9 (1.9, 6.1) days, 3.8 (1.8, 6.8) days, and 3.1 (1.0, 5.7) days, respectively, for the adult population, pediatric cardiac group, and newborns. The treatment was performed using administration synchronized to the mechanical ventilation. The dose was gradually decreased before withdrawal in 86% of the cases according to the usual procedure of each center. Adverse events included rebound effect for 3.4% (95% confidence interval [CI], 0.9%-8.5%) of adults, 1.2% (95% CI, 0.0%-6.7%) of children, and 2.6% (95% CI, 0.1%-13.8%) of neonates and methemoglobinemia exceeded 2.5% for 5 of 62 monitored patients. Other pulmonary vasodilators were associated with NO in 23% of adults, 95% of children, and 23.7% of neonates. ICU stay was respectively 10 (6, 22) days, 7.5 (5.5, 15) days, and 9 (8, 15) days and ICU mortality was 22.2%, 6.2%, and 7.9% for adults, children, and neonates, respectively.

CONCLUSIONS

This study confirms the safety of NO therapy in the 3 populations with a low rate of rebound effect. Gradual withdrawal of NO combined with pulmonary vasodilators are current practices in this population. The use of last-generation NO devices allowed good compliance with recommendations.

Nitric oxide and pulmonary arterial hypertension

The pathogenesis of pulmonary arterial hypertension remains undefined. Changes in the expression and effects mediated by a number of vasoactive factors have been implicated to play a role in the onset and progression of the disease. The source of many of these mediators, such as nitric oxide (NO), prostacyclin and endothelin-1 (ET-1), is the pulmonary endothelium. This article focus in the role of nitric oxide in PAH, reviewing the evidence for its involvement in regulation of pulmonary a vascular tone under physiological conditions, the mechanisms by which it can contribute to the pathological changes seen in PAH and strategies for the use of NO as a therapy for treatment of the disease.

Effect of Inhaled Nitric Oxide on Outcomes in Children With Acute Lung Injury: Propensity Matched Analysis From a Linked Database

OBJECTIVES

To evaluate the effect of inhaled nitric oxide on outcomes in children with acute lung injury.

DESIGN

Retrospective study with a secondary data analysis of linked data from two national databases. Propensity score matching was performed to adjust for potential confounding variables between patients who received at least 24 hours of inhaled nitric oxide (inhaled nitric oxide group) and those who did not receive inhaled nitric oxide (no inhaled nitric oxide group).

SETTING

Linked data from Virtual Pediatric Systems (LLC) database and Pediatric Health Information System.

PATIENTS

Patients less than 18 years old receiving mechanical ventilation for acute lung injury at nine participating hospitals were included (2009-2014).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 20,106 patients from nine hospitals were included. Of these, 859 patients (4.3%) received inhaled nitric oxide for at least 24 hours during their hospital stay. Prior to matching, patients in the inhaled nitric oxide group were younger, with more comorbidities, greater severity of illness scores, higher prevalence of cardiopulmonary resuscitation, and greater resource utilization. Before matching, unadjusted outcomes, including mortality, were worse in the inhaled nitric oxide group (inhaled nitric oxide vs no inhaled nitric oxide; 25.7% vs 7.9%; p < 0.001; standardized mortality ratio, 2.6 [2.3-3.1] vs 1.1 [1.0-1.2]; p < 0.001). Propensity score matching of 521 patient pairs revealed no difference in mortality in the two groups (22.3% vs 20.2%; p = 0.40; standardized mortality ratio, 2.5 [2.1-3.0] vs 2.3 [1.9-2.8]; p = 0.53). However, the other outcomes such as ventilation free days (10.1 vs 13.6 d; p < 0.001), duration of mechanical ventilation (13.8 vs 10.1 d; p < 0.001), duration of ICU and hospital stay (15.5 vs 12.2 d; p < 0.001 and 28.0 vs 24.1 d; p < 0.001), and hospital costs ($150,569 vs $102,823; p < 0.001) were significantly worse in the inhaled nitric oxide group.

CONCLUSIONS

This large observational study demonstrated that inhaled nitric oxide administration in children with acute lung injury was not associated with improved mortality. Rather, it was associated with increased hospital utilization and hospital costs.

Is Administration of Nitric Oxide During Extracorporeal Membrane Oxygenation Associated With Improved Patient Survival?

OBJECTIVE

To evaluate the outcomes associated with the use of inhaled nitric oxide during extracorporeal membrane oxygenation.

DESIGN

Post hoc analysis of data from an existing administrative national database, Pediatric Health Information system (2004-2014). Multivariable logistic regression models were fitted to study the effect of inhaled nitric oxide during extracorporeal membrane oxygenation on study outcomes.

SETTING

Forty-two children's hospitals across the United States.

PATIENTS

Patients in the age group from 1 day through 18 years admitted to an ICU who received extracorporeal membrane oxygenation during their hospital stay were included.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In total, 6,419 patients qualified for inclusion. Of these, inhaled nitric oxide was used among 3,629 patients during extracorporeal membrane oxygenation run. Approximately one half of the study patients received inhaled nitric oxide at extracorporeal membrane oxygenation initiation. The proportion of patients receiving inhaled nitric oxide during extracorporeal membrane oxygenation decreased with increasing duration of extracorporeal membrane oxygenation. After adjusting for patient characteristics and center variables, use of inhaled nitric oxide was not associated with any survival benefit. However, higher proportion of patients receiving inhaled nitric oxide were associated with prolonged hospital length of stay and prolonged duration of extracorporeal membrane oxygenation. In adjusted models, the hospital charges were higher in the inhaled nitric oxide group. The median hospital costs among patients receiving inhaled nitric oxide were higher by $39,732 (95% CI, $31,074-48,390) as compared to the patients who did not receive inhaled nitric oxide, after adjusting for patient (including hospital length of stay) and center level variables. As the duration of inhaled nitric oxide therapy increased, proportion of patients with prolonged duration of extracorporeal membrane oxygenation and prolonged hospital length of stay increased.

CONCLUSIONS

This large observational analysis of use of nitric oxide during extracorporeal membrane oxygenation calls into question the benefits of inhaled nitric oxide among patients receiving extracorporeal membrane oxygenation for pulmonary or cardiac failure. Given our inability to determine type of extracorporeal membrane oxygenation and control for severity of illness, these findings should be interpreted as exploratory.

Adjunctive treatments in pediatric acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a devastating process that involves pulmonary inflammation, alveolar damage and hypoxemic respiratory failure. Although advances in management approaches over the past two decades have resulted in significantly improved outcomes, death from pediatric ARDS may still occur in up to 35% of patients. While invasive mechanical ventilation is an essential component of ARDS management, various adjuncts have been utilized as treatment for these patients. However, evidence-based data in infants and children in this area are lacking. In this article, the authors review the available evidence supporting (or not supporting) the use of non-ventilatory adjunctive strategies in the management of pediatric ARDS, including prone positioning, pulmonary vasodilators, β-agonists, steroids and surfactant.

Reactive oxygen and nitrogen species in pulmonary hypertension

Pulmonary vascular disease can be defined as either a disease affecting the pulmonary capillaries and pulmonary arterioles, termed pulmonary arterial hypertension, or a disease affecting the left ventricle, called pulmonary venous hypertension. Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary circulation characterized by endothelial dysfunction, as well as intimal and smooth muscle proliferation. Progressive increases in pulmonary vascular resistance and pressure impair the performance of the right ventricle, resulting in declining cardiac output, reduced exercise capacity, right-heart failure, and ultimately death. While the primary and heritable forms of the disease are thought to affect over 5000 patients in the United States, the disease can occur secondary to congenital heart disease, most advanced lung diseases, and many systemic diseases. Multiple studies implicate oxidative stress in the development of PAH. Further, this oxidative stress has been shown to be associated with alterations in reactive oxygen species (ROS), reactive nitrogen species (RNS), and nitric oxide (NO) signaling pathways, whereby bioavailable NO is decreased and ROS and RNS production are increased. Many canonical ROS and NO signaling pathways are simultaneously disrupted in PAH, with increased expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and xanthine oxidoreductase, uncoupling of endothelial NO synthase (eNOS), and reduction in mitochondrial number, as well as impaired mitochondrial function. Upstream dysregulation of ROS/NO redox homeostasis impairs vascular tone and contributes to the pathological activation of antiapoptotic and mitogenic pathways, leading to cell proliferation and obliteration of the vasculature. This paper will review the available data regarding the role of oxidative and nitrosative stress and endothelial dysfunction in the pathophysiology of pulmonary hypertension, and provide a description of targeted therapies for this disease.

GTP cyclohydrolase I expression is regulated by nitric oxide: role of cyclic AMP

Our previous studies have demonstrated that nitric oxide (NO) leads to nitric oxide synthase (NOS) uncoupling and an increase in NOS-derived superoxide. However, the cause of this uncoupling has not been adequately resolved. The pteridine cofactor tetrahydrobiopterin (BH(4)) is a critical determinant of endothelial NOS (eNOS) activity and coupling, and GTP cyclohydrolase I (GCH1) is the rate-limiting enzyme in its generation. Thus the initial purpose of this study was to determine whether decreases in BH(4) could underlie, at least in part, the NO-mediated uncoupling of eNOS we have observed both in vitro and in vivo. Initially we evaluated the effect of inhaled NO levels on GCH1 expression and BH(4) levels in the intact lamb. Contrary to our hypothesis, we found that there was a significant increase in both plasma BH4 levels and peripheral lung GCH1 protein levels. Furthermore, in vitro, we found that exposure to the NO donor spermine NONOate (SPNONO) led to an increase in GCH1 protein and BH(4) levels in both COS-7 and pulmonary arterial endothelial cells. However, SPNONO treatment also caused a significant increase in phospho-cAMP response element binding protein (CREB) levels, as detected by Western blot analysis, and significantly increased cAMP levels, as detected by enzyme immunoassay. Furthermore, utilizing GCH1 promoter fragments fused to a luciferase reporter gene, we found that GCH1 promoter activity was enhanced by SPNONO in a CREB-dependent manner, and electromobility shift assays revealed an NO-dependent increase in the nuclear binding of CREB. These data suggest that NO increases BH(4) levels through a cAMP/CREB-mediated increase in GCH1 transcription and that the eNOS uncoupling associated with exogenous NO does not involved reduced BH(4) levels.

The nitric oxide/cGMP signaling pathway in pulmonary hypertension

This article briefly reviews the background of endothelium-dependent vasorelaxation, describes the nitric oxide/cGMP/protein kinase pathway and its role in modulating pulmonary vascular tone and remodeling, and describes three approaches that target the nitric oxide/cGMP pathway in the treatment of patients with pulmonary arterial hypertension.

Effect of Inhaled Iloprost during Off-Medication Time in Patients with Pulmonary Arterial Hypertension

BACKGROUND

Iloprost is a stable prostacyclin analogue that is associated with a longer duration of vasodilatation and has been approved for inhalative use with 6 or 9 inhalations during the daytime and a night pause. It is not known if during the night pause rebound pulmonary hypertension occurs. The aim of this study was to assess the hemodynamics in iloprost-treated patients during the daytime and at night.

METHODS

We enrolled 5 adult patients (aged 45 +/- 10 years) with idiopathic pulmonary arterial hypertension (IPAH) and chronic inhaled iloprost therapy for at least 12 months. Further medication remained unchanged during the study period. Hemodynamics were monitored by right heart catheterization.

RESULTS

After 30-60 min of nebulized iloprost, mean pulmonary arterial pressures (PAP) decreased from 68 +/- 15 to 51 +/- 18 mm Hg (p = 0.004). After 6 h off-medication sleeping time, mean PAP initially increased until 2 a.m. and decreased subsequently until wake-up time at 6 a.m. Mean PAP, cardiac index and pulmonary vascular resistance at night were not significantly different from the values during the day.

CONCLUSIONS

In this study, patients with IPAH and chronic nebulized iloprost therapy did not reveal a rebound pulmonary hypertension during off-medication sleeping time.

Oxidative and nitrosative stress in pediatric pulmonary hypertension: roles of endothelin-1 and nitric oxide

An increasing number of studies implicate oxidative stress in the development of endothelial dysfunction and the pathogenesis of cardiovascular disease. Further, this oxidative stress has been shown to be associated with alterations in both the endothelin-1 (ET-1) and nitric oxide (NO) signaling pathways such that bioavailable NO is decreased and ET-1 signaling is potentiated. However, recent data, from our groups and others, have shown that oxidative stress, ET-1, and NO are co-regulated in a complex fashion that appears to be dependent on the cellular levels of each species. Thus, when ROS levels are transiently elevated, NO signaling is potentiated through transcriptional, post-transcriptional, and post-translational mechanisms. However, in pediatric pulmonary hypertensive disorders, when reactive oxygen species (ROS) increases are sustained by ET-1 mediated activation of smooth muscle cell ET(A) subtype receptors, NOS gene expression and NO signaling are reduced. Further, increases in oxidative stress can stimulate both the expression of the ET-1 gene and the secretion of the ET-1 peptide. Finally, the addition of exogenous NO, and increasingly utilized therapy for pulmonary hypertension, can also lead to increases ROS generation via the activation of ROS generating enzymes and through the induction of mitochondrial dysfunction. Thus, this manuscript will review the available data regarding the interaction of oxidative and nitrosative stress, endothelial dysfunction, and its role in the pathophysiology of pediatric pulmonary hypertension. In addition, we will suggest avenues of both basic and clinical research that will be important to develop novel pulmonary hypertension treatment and prevention strategies, and resolve some of the remaining clinical issues regarding the use of NO augmentation.

Molecular mechanisms of nitric oxide-induced growth arrest and apoptosis in fetal pulmonary arterial smooth muscle cells

Superoxide plays an important role in pulmonary arterial smooth muscle cell (SMC) proliferation and survival. The rapid reaction between superoxide and nitric oxide (NO) to form peroxynitrite suggests that endothelium-derived NO may influence adjacent SMC growth. To investigate this possibility, we determined the dose-dependent effects of NO on the proliferation and viability of pulmonary arterial SMC isolated from fetal lambs (FPASMC). Using fluorescence microscopy we found a dose-dependent decrease in superoxide levels in FPASMC treated with the NO donor spermine NONOate. This was associated with an increase in peroxynitrite-mediated protein nitration. At doses between 50 and 250 microM, spermine NONOate attenuated serum-induced FPASMC proliferation resulting in a G(0)/G(1) cell cycle arrest. This process involved a decrease in levels of cyclin A and an increase in the nuclear localization of p21 and p27. Furthermore, 500 microM spermine NONOate decreased viable cell number by inducing programmed cell death: FPASMC treated with 500 microM spermine NONOate displayed a loss of mitochondrial membrane potential, followed by caspase activation and DNA fragmentation. These data suggest that NO inhibits superoxide-induced proliferation of FPASMC and at higher doses induces apoptosis. NO donors may therefore prove to be useful therapeutic tools to treat diseases resulting from excessive proliferation of vascular smooth muscle.

Endothelial alterations during inhaled NO in lambs with pulmonary hypertension: implications for rebound hypertension

Clinically significant increases in pulmonary vascular resistance (PVR) have been noted upon acute withdrawal of inhaled nitric oxide (iNO). Previous studies in the normal pulmonary circulation demonstrate that iNO increases endothelin-1 (ET-1) levels and decreases endogenous nitric oxide synthase (NOS) activity, implicating an endothelial etiology for the increase in resistance upon iNO withdrawal. However, the effect of iNO on endogenous endothelial function in the clinically relevant pulmonary hypertensive circulation is unknown. The objective of this study was to determine the effects of iNO on endogenous NO-cGMP and ET-1 signaling in lambs with preexisting pulmonary hypertension secondary to increased pulmonary blood flow. Eight fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt lambs). After delivery (4 wk), the shunt lambs were mechanically ventilated with iNO (40 ppm) for 24 h. After 24 h of inhaled NO, plasma ET-1 levels increased by 34.8% independently of changes in protein levels (P < 0.05). Contrary to findings in normal lambs, total NOS activity did not decrease during iNO. In fact, Western blot analysis demonstrated that tissue endothelial NOS protein levels decreased by 43% such that NOS activity relative to protein levels actually increased during iNO (P < 0.05). In addition, the beta-subunit of soluble guanylate cyclase decreased by 70%, whereas phosphodiesterase 5 levels were unchanged (P < 0.05). Withdrawal of iNO was associated with an acute increase in PVR, which exceeded baseline PVR by 45%, and a decrease in cGMP concentrations to levels that were below baseline. These data suggest that the endothelial response to iNO and the potential mechanisms of rebound pulmonary hypertension are dependent upon the underlying pulmonary vasculature.

Phosphodiesterase-3 inhibition prevents the increase in pulmonary vascular resistance following inhaled nitric oxide withdrawal in lambs

OBJECTIVES

To determine the effects of inhaled nitric oxide on endogenous cyclic adenosine monophosphate in the intact lamb, and to determine the potential role of cyclic adenosine monophosphate in the rebound pulmonary hypertension associated with nitric oxide withdrawal.

DESIGN

Prospective, placebo-controlled experimental study.

SETTING

University-based basic science research laboratory.

SUBJECTS

One-month-old lambs.

INTERVENTIONS

Six 1-month-old control lambs, and 6 milrinone- (phosphodiesterase-3 inhibitor) treated lambs, were mechanically ventilated. Inhaled nitric oxide (40 ppm) was administered for 24 hrs and then acutely withdrawn. Sequential peripheral lung biopsies were obtained before, during, and 2 hrs after withdrawing inhaled nitric oxide therapy.

MEASUREMENTS AND MAIN RESULTS

In control lambs, initiation of nitric oxide decreased left pulmonary vascular resistance by 29.6%, and withdrawal rapidly increased pulmonary vascular resistance by 77.1% (p <.05). Lung tissue cyclic adenosine monophosphate concentrations decreased by 25.3% during nitric oxide therapy (p <.05). In milrinone-treated lambs, nitric oxide decreased pulmonary vascular resistance by 26.6% (p <.05), but pulmonary vascular resistance was unchanged after acute withdrawal. Lung tissue cyclic adenosine monophosphate concentrations were preserved during nitric oxide therapy.

CONCLUSIONS

Inhaled nitric oxide produces potent pulmonary vasodilation by activating soluble guanylate cyclase and increasing smooth muscle cell concentrations of guanosine-3',5'-cyclic monophosphate. However, alterations in endogenous nitric oxide/guanosine-3',5'-cyclic monophosphate during inhaled nitric oxide have been implicated in the clinically significant increases in pulmonary vascular resistance noted upon its acute withdrawal. Previous in vitro data suggest that exogenous nitric oxide/guanosine-3',5'-cyclic monophosphate can also alter cyclic adenosine monophosphate concentrations via their effect on cyclic adenosine monophosphate production and metabolism. The current in vivo study demonstrates that lung tissue cyclic adenosine monophosphate concentrations are decreased during inhaled nitric oxide and suggests a role for decreased cyclic adenosine monophosphate in the rebound pulmonary hypertension noted upon inhaled nitric oxide withdrawal. Milrinone may be a useful adjunct therapy during inhaled nitric oxide to preserve cyclic adenosine monophosphate concentrations and prevent rebound pulmonary hypertension.

Prostacyclin and its analogues in the treatment of pulmonary hypertension

Prostacyclin and its analogues (prostanoids) are potent vasodilators and possess antithrombotic and antiproliferative properties. All of these properties help to antagonize the pathological changes that take place in the small pulmonary arteries of patients with pulmonary hypertension. Indeed, several prostanoids have been shown to be efficacious to treat pulmonary hypertension, while the main mechanism underlying the beneficial effects remains unknown. There are indications of beneficial combination effects of prostaglandins and phosphodiesterase inhibitors and endothelin receptor antagonists. This speaks in favor of combination therapies for pulmonary hypertension in the future. The mode of application of prostanoids used in randomized controlled studies has been quite variable: continuous i.v. infusion of prostacyclin, continuous s.c. infusion of treprostinil, p.o. application of beraprost, and inhaled application of iloprost. In addition, the applied doses were quite different, ranging from 0.25 ng/kg/min for inhaled iloprost to 30-50 ng/kg/min for i.v. prostacyclin. While the principal pharmacological properties of all prostanoids are very similar due to a main action on IP receptors, there are considerable differences in pharmacokinetics and metabolism, with half-lives of 2 min for prostacyclin and about 34 min for treprostinil for i.v. infused drugs and half-lives of about 85 min for s.c. infused treprostinil. In addition, the adverse effects largely depend on the doses used and the mode of application, although there is great variability between subjects. It remains to be determined which patients will profit most from which substance (or combination) and mode of application.

Phosphodiesterase inhibitors for persistent pulmonary hypertension of the newborn: a review

Persistent pulmonary hypertension of the newborn (PPHN) is a complex syndrome with multiple causes, with an incidence of 0.43-6.8/1,000 live births and a mortality of 10-20%. Survivors have high morbidity in the forms of neurodevelopmental and audiological impairment, cognitive delays, hearing loss, and a high rate of rehospitalization. The optimal approach to the management of PPHN remains controversial. Inhaled nitric oxide (iNO) is currently regarded as the gold standard therapy, but with as many as 30% of cases failing to respond, has not proven to be the single magic bullet. Given the complex pathophysiology of the disease, any such magic bullet is unlikely. A number of recent studies have suggested a role for specific phosphodiesterase (PDE) inhibitors in the management of PPHN. Sildenafil, a specific PDE5 inhibitor, appears the most promising of such agents. We aim to review the current status and limitations of iNO and the potential of PDE inhibitors in the management of PPHN. The reasons why caution is warranted before specific PDE5 inhibitors like sildenafil are labelled as potential magic bullets for PPHN will be discussed. The need for randomized-controlled trials to determine the safety, efficacy, and long-term outcome following treatment with sildenafil in PPHN is emphasized.

Role of reactive oxygen species in vascular remodeling associated with pulmonary hypertension

Several manifestations of neonatal pulmonary hypertension are associated with vascular remodeling, resulting in increased muscularity of the small pulmonary arteries. Abnormal structural development of the pulmonary vasculature has been implicated in persistent pulmonary hypertension of the newborn (PPHN). Increased plasma levels of the vasoconstrictor endothelin-1 (ET-1) have been demonstrated in patients with PPHN, which is likely to contribute to hypertension. In addition, several studies have identified a role for ET-1 in the proliferation of vascular smooth muscle cells (SMCs), suggesting that ET-1 may also be involved in the vascular remodeling characteristic of this disease. However, the mechanisms of ET-1-induced SMC proliferation are unclear and appear to differ between cells from different origins within the vasculature. In SMCs isolated from fetal pulmonary arterial cells, ET-1 stimulated proliferation via an induction of reactive species (ROS). Furthermore, other lines of evidence have demonstrated the involvement of ROS in ET-1-stimulated SMC growth, suggesting that ROS may be a common factor in the mechanisms involved. This review discusses the potential roles for ROS in the abnormal pulmonary vascular development characteristic of PPHN, and the treatment strategies arising from our increasing knowledge of the molecular mechanisms involved.

Pharmacodynamics and Pharmacokinetics of Inhaled Iloprost, Aerosolized by Three Different Devices, in Severe Pulmonary Hypertension

BACKGROUND

Inhalation of iloprost, a stable prostacyclin analog, is an effective therapy for pulmonary hypertension with few side effects. This approach may, however, be handicapped by limitations of currently available nebulization devices. We assessed whether the physical characterization of a device is sufficient to predict drug deposition and pharmacologic effects.

METHODS

We investigated the effects of a standardized iloprost aerosol dose (5 micro g; inhaled within approximately 10 min) in 12 patients with severe pulmonary hypertension in a crossover design employing three well-characterized nebulizers. The nebulizers use different techniques to increase efficiency and alveolar targeting (Ilo-Neb/Aerotrap [Nebu-Tec; Elsenfeld, Germany], Ventstream [MedicAid; Bognor Regis, UK], and HaloLite [Profile Therapeutics; Bognor Regis, UK]). Measurements were performed using a Swan-Ganz catheter and determination of arterial iloprost plasma levels.

RESULTS

During inhalation of iloprost, the pulmonary vascular resistance decreased substantially (baseline, approximately 1,250 dyne.s.cm(-5); decrease, - 35.5 to - 38.0%) and pulmonary artery pressure decreased substantially (baseline, approximately 58 mm Hg; decline, - 18.4 to -21.8%), whereas the systemic arterial pressure was largely unaffected. Cardiac output and mixed venous and arterial oxygen saturation displayed a marked increase. The pharmacodynamic profiles with the three devices were superimposable. Moreover, rapid entry of iloprost into the systemic circulation was noted, peaking immediately after termination of the inhalation maneuver, with very similar maximum serum concentrations (158 pg/mL, 155 pg/mL, and 157 pg/mL), and half-lives of serum levels (6.5 min, 9.4 min, and 7.7 min) for the three nebulizers, respectively. Interestingly, the "half-life" of the pharmacodynamic effects in the pulmonary vasculature (eg, decrease in pulmonary vascular resistance, ranging between 21 and 25 min) clearly outlasted this serum level-based pharmacokinetic half-life.

CONCLUSIONS

A standardized dose of aerosolized iloprost delivered by different nebulizer types induces comparable pharmacodynamic and pharmacokinetic responses. Pulmonary vasodilation, persisting after disappearance of the drug from the systemic circulation, supports the hypothesis that local drug deposition largely contributes to the preferential pulmonary vasodilation in response to inhaled iloprost.

Nitric oxide activates p21ras and leads to the inhibition of endothelial NO synthase by protein nitration

Recent data has indicated that exogenous nitric oxide (NO) has the ability to decrease endogenous NO production by inhibiting the enzyme responsible for its generation, NO synthase (NOS). Our previous studies have indicated that increased generation of reactive oxygen species (ROS) play an important role in the inhibitory event. However, the mechanisms for these effects remain unclear. Previous studies have suggested that NO can activate p21ras. Thus, the objective of this study was to determine whether NO-mediated activation of p21ras is involved in the inhibitory process, and to further elucidate the involvement of ROS. Using primary cultures of ovine pulmonary arterial endothelial cells we demonstrated that the NO donor SpermineNONOate, increased p21ras activity by 2.3-fold compared to untreated cells, and that the farnesyl-transferase inhibitor, alpha-hydroxyfarnesylphosphonic acid, reduced p21ras activity and significantly reduced inhibition of eNOS. The overexpression of p21ras increased, while the overexpression of an NO unresponsive mutant of p21ras (p21ras C118S) reduced, the inhibition of eNOS by NO. Further, we identified an increase in the level of superoxide and peroxynitrite in endothelial cells exposed to NO that was reduced by p21ras C118S transient transfection. Conversely, levels of superoxide and peroxynitrite could be increased by the over expression of wild type p21ras. Similarly, eNOS nitration induced by NO exposure was reduced by p21ras C118S transient transfection, and increased by the overexpression of wild-type p21ras. Finally, results also demonstrated that eNOS itself was a significant producer of superoxide, and that this appeared to be related to a p21ras-dependent increase in phosphorylation of Ser1177. Our results implicate a signaling pathway involving p21ras activation, superoxide generation, and peroxynitrite formation as being important in the NO-mediated inhibition of eNOS.

[Effects of prone position, inhaled nitric oxide and surfactant in children with hypoxemic pulmonary disease]

OBJECTIVE

To analyze the therapeutic response to prone position, inhaled nitric oxide (NO) and surfactant in children with hypoxemic pulmonary disease.

PATIENTS AND METHODS

We studied the effect of prone position, NO, and surfactant in critically ill children with acute hypoxemic pulmonary disease unresponsive to conventional therapy. We analyzed PaO2, SatO2, the PaO2/FiO2 ratio, oxygenation index and PaCO2 before and after each treatment, as well as the subsequent clinical course. An increase of more than 20 % in the PaO2/FiO2 ratio was considered a positive response.

RESULTS

Ninety treatments were administered in 56 patients: 55 patients were treated with NO, 18 with prone position and 17 with surfactant. All three treatments substantially improved oxygenation. The mean increase in the PaO2/FiO2 ratio was 35 % with nitric oxide, 33 % with prone position and 50 % with surfactant. The mean decrease in oxygenation index was 22 % with nitric oxide, 24 % with prone position and 17 % with surfactant. Seventy-one percent of patients treated with NO, 61 % of patients treated with prone position, and 64 % of patients who received surfactant were responders. The three treatments produced a slight decrease in PaCO2 (2.5 mmHg with nitric oxide, 4.7 mmHg with prone position and 5.1 mmHg with surfactant).

CONCLUSIONS

Inhaled NO, prone position and surfactant improve oxygenation in some children with hypoxic pulmonary disease.

Tratamientos complementarios: óxido nítrico, posición en prono y surfactante

The management of hypoxic respiratory failure is based on oxygen delivery and ventilatory support with lung-protective ventilation strategies. Better understanding of acute lung injury have led to new therapeutic approaches that can modify the outcome of these patients. These adjunctive oxygenation strategies include inhaled nitric oxide and surfactant delivery, and the use of prone positioning. Nitric oxide is a selective pulmonary vasodilator that when inhaled, improves oxygenation in clinical situations such as persistent pulmonary hypertension of the newborn, pulmonary hypertension associated with congenital heart disease, and acute respiratory distress syndrome (ARDS). When applied early in ARDS, prone positioning improves distribution of ventilation and reduces the intrapulmonary shunt. The surfactant has dramatically decreased mortality caused by hyaline membrane disease in premature newborns, although the results have been less successful in ARDS. Greater experience is required to determine whether the combination of these treatments will improve the prognosis of these patients.

Inhaled iloprost for severe pulmonary hypertension

BACKGROUND

Uncontrolled studies suggested that aerosolized iloprost, a stable analogue of prostacyclin, causes selective pulmonary vasodilatation and improves hemodynamics and exercise capacity in patients with pulmonary hypertension.

METHODS

We compared repeated daily inhalations of 2.5 or 5.0 microg of iloprost (six or nine times per day; median inhaled dose, 30 microg per day) with inhalation of placebo. A total of 203 patients with selected forms of severe pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension (New York Heart Association [NYHA] functional class III or IV) were included. The primary end point was met if, after week 12, the NYHA class and distance walked in six minutes were improved by at least one class and at least 10 percent, respectively, in the absence of clinical deterioration according to predefined criteria and death.

RESULTS

The combined clinical end point was met by 16.8 percent of the patients receiving iloprost, as compared with 4.9 percent of the patients receiving placebo (P=0.007). There were increases in the distance walked in six minutes of 36.4 m in the iloprost group as a whole (P=0.004) and of 58.8 m in the subgroup of patients with primary pulmonary hypertension. Overall, 4.0 percent of patients in the iloprost group (including one who died) and 13.7 percent of those in the placebo group (including four who died) did not complete the study (P=0.024); the most common reason for withdrawal was clinical deterioration. As compared with base-line values, hemodynamic values were significantly improved at 12 weeks when measured after iloprost inhalation (P<0.001), were largely unchanged when measured before iloprost inhalation, and were significantly worse in the placebo group. Further significant beneficial effects of iloprost treatment included an improvement in the NYHA class (P=0.03), dyspnea (P=0.015), and quality of life (P=0.026). Syncope occurred with similar frequency in the two groups but was more frequently rated as serious in the iloprost group, although this adverse effect was not associated with clinical deterioration.

CONCLUSIONS

Inhaled iloprost is an effective therapy for patients with severe pulmonary hypertension.

The endothelin A receptor antagonists PD 156707 (CI-1020) and PD 180988 (CI-1034) reverse the hypoxic pulmonary vasoconstriction in the perinatal lamb

Endothelin-1 (ET-1) is considered an intermediary in the constrictor response of the pulmonary vasculature to hypoxia and, by extension, is assigned a prime role in the pathogenesis of pulmonary hypertension. We report here the antihypertensive action in the conscious newborn lamb of two novel endothelin A receptor antagonists, sodium 2-benzo-[1,3]dioxol-5-yl-4- (4-methoxy-phenyl)-4-oxo-3-(3,4,5-trimethoxy-benzyl)-but-2- enoate (PD 156707) and 4-(7-ethyl-benzo[1,3]dioxol-5-yl)-1, 1-dioxo-2-(2-trifluoromethyl-phenyl)-1,2-dihydro-1l6-benzo-[e][1,2]thiazine-3-carboxylic acid potassium (PD 180988), differing in chemical properties and half-life within the body. PD 156707 and PD 180988, given in the right atrium as a bolus followed by infusion, had little or no effect on pulmonary and systemic hemodynamics under normoxia. Conversely, they both reversed the pulmonary hypertension due to alveolar hypoxia while producing minor changes, or no change at all, in systemic vascular resistance. Furthermore, their pulmonary vascular effect outlasted administration. Pulmonary hypertension being elicited by infusion of the thromboxane A(2) analog, 9,11-epithio-11,12-methano-thromboxane A(2) (ONO-11113) was instead not amenable to ET(A)R inhibition. Blood levels of ET-1, which rose with hypoxia but not ONO-11113 treatment, were not changed by either antagonist. Consistent with findings in vivo, when using isolated pulmonary resistance arteries from term fetal lamb, PD 156707 curtailed the hypoxia- but not the ONO-11113-induced constriction. We conclude that PD 156707 and PD 180988 are selective inhibitors of pulmonary vasoconstriction resulting from hypoxia. Our findings support the use of these or allied compounds in the management of pulmonary hypertension in the neonate.

Inhaled nitric oxide in cardiology

Inhaled nitric oxide (INO) allows selective pulmonary vasodilatation with rapidity of action. It is effective in the acute management of reversible pulmonary hypertension in cardiac medical and surgical patients and is also useful in assessing the pulmonary vasodilator capacity in patients with chronic pulmonary hypertension. This review will examine the role of INO in the management of cardiac patients, compared to alternatives where available. The use of INO in cardiac failure, post-operative cardiac patients, patients with congestive cardiac failure or congenital heart disease will also be reviewed. Newer alternatives with prolonged pulmonary activity and simpler administration are also discussed.

Inhaled nitric oxide-induced rebound pulmonary hypertension: role for endothelin-1

Clinically significant increases in pulmonary vascular resistance have been noted on acute withdrawal of inhaled nitric oxide (NO). Endothelin (ET)-1 is a vasoactive peptide produced by the vascular endothelium that may participate in the pathophysiology of pulmonary hypertension. The objectives of this study were to determine the effects of inhaled NO on endogenous ET-1 production in vivo in the intact lamb and to determine the potential role of ET-1 in the rebound pulmonary hypertension associated with the withdrawal of inhaled NO. Seven 1-mo-old vehicle-treated control lambs and six PD-156707 (an ET(A) receptor antagonist)-treated lambs were mechanically ventilated. Inhaled NO (40 parts per million) was administered for 24 h and then acutely withdrawn. After 24 h of inhaled NO, plasma ET-1 levels increased by 119.5 +/- 42.2% (P < 0.05). Western blot analysis revealed that protein levels of preproET-1, endothelin-converting enzyme-1alpha, and ET(A) and ET(B) receptors were unchanged. On acute withdrawal of NO, pulmonary vascular resistance (PVR) increased by 77.8% (P < 0.05) in control lambs but was unchanged (-5.5%) in PD-156707-treated lambs. Inhaled NO increased plasma ET-1 concentrations but not gene expression in the intact lamb, and ET(A) receptor blockade prevented the increase in PVR after NO withdrawal. These data suggest a role for ET-1 in the rebound pulmonary hypertension noted on acute withdrawal of inhaled NO.

Randomized controlled study of inhaled nitric oxide after operation for congenital heart disease

BACKGROUND

Inhaled nitric oxide selectively decreases pulmonary vascular resistance. This study was performed to determine whether inhaled nitric oxide decreases the incidence of pulmonary hypertensive crises after corrective procedures for congenital heart disease.

METHODS

Patients with a systolic pulmonary arterial pressure of 50% or more of the systolic systemic arterial pressure during the early postoperative period were randomized to receive 20 parts per million inhaled nitric oxide (n = 20) or conventional therapy alone (n = 20). Acute hemodynamic and blood gas measurements were performed at the onset of therapy. The efficacy of sustained therapy was determined by comparing the number of patients in each group who experienced a pulmonary hypertensive crisis.

RESULTS

In comparison to controls, there were no significant differences in the baseline and 1-hour measurements of patients who were treated with nitric oxide. Four patients in the control group and 3 patients in the nitric oxide group experienced a pulmonary hypertensive crisis.

CONCLUSIONS

Nitric oxide did not substantially improve pulmonary hemodynamics and gas exchange immediately after operation for congenital heart disease. Nitric oxide also failed to significantly decrease the incidence of pulmonary hypertensive crises.

Nitric oxide in the lung: therapeutic and cellular mechanisms of action

Nitric oxide is produced by many cell types in the lung and plays an important physiologic role in the regulation of pulmonary vasomotor tone by several known mechanisms. Nitric oxide stimulates soluble guanylyl cyclase, resulting in increased levels of cyclic GMP in lung smooth muscle cells. The gating of K+ and Ca2+ channels by cyclic GMP binding is thought to play a role in nitric oxide-mediated vasodilation. Nitric oxide may also regulate pulmonary vasodilation by direct activation of K+ channels or by modulating the expression and activity of angiotensin II receptors. Administration of nitric oxide by inhalation has been shown to acutely improve hypoxemia associated with pulmonary hypertension in humans and animals. This is presumably due to its ability to induce pulmonary vasodilation. Inhaled nitric oxide improves oxygenation and reduces the need for extracorporeal membrane oxygenation in term and near-term infants with persistent pulmonary hypertension. However, long-term benefits to these infants have been difficult to demonstrate. In other pathologic conditions, such as prematurity and acute respiratory distress syndrome, short-term benefits have not been shown conclusively to outweigh potential toxicities. For example, high-dose inhaled nitric oxide decreases surfactant function in the lung. Inhaled nitric oxide also acts as a pulmonary irritant, causing priming of lung macrophages and oxidative damage to lung epithelial cells. Conversely, protective effects of nitric oxide have been described in a number of pathological states, including hyperoxic and ischemia/reperfusion injury. Nitric oxide has also been reported to protect against oxidative damage induced by other reactive intermediates, including superoxide anion and hydroxyl radical. The dose and timing of nitric oxide administration needs to be ascertained in clinical trials before recommendations can be made regarding its optimal use in patients.

Why is the pathology of falciparum worse than that of vivax malaria?

Here, Ian Clark and Bill Cowden summarize new evidence suggesting that nitric oxide (NO) generated by inducible NO synthase (iNOS) provides a functional link between the previously competing approaches to malarial disease pathogenesis: ischaemic hypoxia and NO. When combined with the newly recognized roles of iNOS in renal and pulmonary function and glucose metabolism, synergy between inflammatory cytokines and hypoxia in iNOS induction provides a framework to help explain, at a molecular level, the differences in the pathology seen in falciparum and vivax malaria. Thus sequestration, through localized hypoxia, might contribute to pathology by enhancing cytokine-induced iNOS. Generalized hypoxia might have the same effect.

Inhaled nitric oxide inhibits NOS activity in lambs: potential mechanism for rebound pulmonary hypertension

Life-threatening increases in pulmonary vascular resistance have been noted on acute withdrawal of inhaled nitric oxide (NO), although the mechanisms remain unknown. In vitro data suggest that exogenous NO exposure inhibits endothelial NO synthase (NOS) activity. Thus the objectives of this study were to determine the effects of inhaled NO therapy and its acute withdrawal on endogenous NOS activity and gene expression in vivo in the intact lamb. Six 1-mo-old lambs were mechanically ventilated and instrumented to measure vascular pressures and left pulmonary blood flow. Inhaled NO (40 ppm) acutely decreased left pulmonary vascular resistance by 27. 5 +/- 4.7% (P < 0.05). This was associated with a 207% increase in plasma cGMP concentrations (P < 0.05). After 6 h of inhaled NO, NOS activity was reduced to 44.3 +/- 5.9% of pre-NO values (P < 0.05). After acute withdrawal of NO, pulmonary vascular resistance increased by 52.1 +/- 11.6% (P < 0.05) and cGMP concentrations decreased. Both returned to pre-NO values within 60 min. One hour after NO withdrawal, NOS activity increased by 48.4 +/- 19.1% to 70% of pre-NO values (P < 0.05). Western blot analysis revealed that endothelial NOS protein levels remained unchanged throughout the study period. These data suggest a role for decreased endogenous NOS activity in the rebound pulmonary hypertension noted after acute withdrawal of inhaled NO.

Nitric oxide inhalation in pulmonary hypertension and severe respiratory failure

Inhalation of nitric oxide (NO) can cause selective pulmonary vasodilation in aerated lung regions; thus, it may be of benefit in the treatment of various forms of pulmonary hypertension and respiratory distress due to a mismatch of pulmonary ventilation and perfusion. The specific characteristics of inhaled NO exclude long-term treatment, but NO has been successfully used as a test substance to screen patients for response to oral vasodilators. Furthermore, inhalation of NO has been shown to improve gas exchange and right ventricular performance and to reduce the need for other, more invasive therapies in various settings of acute pulmonary hypertension. However, the improvement of arterial oxygenation seen in patients with the acute respiratory distress syndrome does not result in increased survival, questioning the future importance of inhaled NO in the treatment of this pulmonary disorder.

Modulation of inflammation and immunity by arginine supplements

Arginine holds a key position in the cellular functions and interactions that occur during inflammation and immune responses. The competition for arginine as a substrate between nitric oxide synthase and arginase appears to be at the core of the regulation of the inflammatory process. This review examines some of the recently defined effects of arginine on various inflammatory processes and immune cell functions.