Inhaled nitric oxide and related therapies

Inhaled Nitric Oxide ReDuce postoperatIve pulmoNAry complicaTions in patiEnts with recent COVID-19 infection (INORDINATE): protocol for a randomised controlled trial

BACKGROUND

A history of SARS-CoV-2 infection has been reported to be associated with an increased risk of postoperative pulmonary complications (PPCs). Even mild PPCs can elevate the rates of early postoperative mortality, intensive care unit (ICU) admission and prolong the length of ICU and/or hospital stays. Consequently, it is crucial to develop perioperative management strategies that can mitigate these increased risks in surgical patients who have recently been infected with SARS-CoV-2. Accumulating evidence suggests that nitric oxide (NO) inhalation might be effective in treating COVID-19. NO functions in COVID-19 by promoting vasodilation, anticoagulation, anti-inflammatory and antiviral effects. Therefore, our study hypothesises that the perioperative use of NO can effectively reduce PPCs in patients with recent SARS-CoV-2 infection.

METHOD AND ANALYSIS

A prospective, double-blind, single-centre, randomised controlled trial is proposed. The trial aims to include participants who are planning to undergo surgery with general anaesthesia and have been recently infected with SARS-CoV-2 (within 7 weeks). Stratified allocation of eligible patients will be performed at a 1:1 ratio based on the predicted risk of PPCs using the Assess Respiratory Risk in Surgical Patients in Catalonia risk index and the time interval between infection and surgery.The primary outcome of the study will be the presence of PPCs within the first 7 days following surgery, including respiratory infection, respiratory failure, pleural effusion, atelectasis, pneumothorax, bronchospasm and aspiration pneumonitis. The primary outcome will be reported as counts (percentage) and will be compared using a two-proportion χ2 test. The common effect across all primary components will be estimated using a multiple generalised linear model.

ETHICS AND DISSEMINATION

The trial is approved by the Institutional Review Board of Xijing Hospital (KY20232058-F1). The findings, including positive, negative and inconclusive results, will be published in scientific journals with peer-review processes.

TRIAL REGISTRATION NUMBER

NCT05721144.

Dead space ratio as a tool in nitric oxide weaning: a study in pulmonary hypertensive disease

OBJECTIVES

To describe the association between successful weaning of inhaled nitric oxide and trends in dead space ratio during such weans in patients empirically initiated on nitric oxide therapy out of concern of pulmonary hypertensive crisis.

PATIENTS

Children in a cardiac intensive care unit initiated on inhaled nitric oxide out of clinical concern for pulmonary hypertensive crisis retrospectively over 2 years.

MEASUREMENTS AND MAIN RESULTS

Twenty-seven patients were included, and nitric oxide was successfully discontinued in 23/27. These patients exhibited decreases in dead space ratio (0.18 versus 0.11, p = 0.047) during nitric oxide weaning, and with no changes in dead space ratio between pre- and post-nitric oxide initiation (p = 0.88) and discontinuation (p = 0.63) phases. These successful patients had a median age of 10 months [4.0, 57.0] and had a pre-existent diagnosis of CHD in 6/23 and pulmonary hypertension in 2/23. Those who failed nitric oxide discontinuation trended with a higher dead space ratio at presentation (0.24 versus 0.10), were more likely to carry a prior diagnosis of pulmonary hypertension (50% versus 8.7%), and had longer mechanical ventilation days (5 versus 12).

CONCLUSIONS

Patients empirically placed on nitric oxide out of concern of pulmonary hypertensive crisis and successfully weaned off showed unchanged or decreased dead space ratio throughout the initiation to discontinuation phases of nitric oxide therapy. Trends in dead space ratio may aid in determining true need for nitric oxide and facilitate effective weaning. Further studies are needed to directly compare trends between success and failure groups.

Delivery of Inhaled Nitric Oxide During MRI to Ventilated Neonates and Infants

BACKGROUND

Many pediatric and neonatal ICU patients receive nitric oxide (NO), with some also requiring magnetic resonance imaging (MRI) scans. MRI-compatible NO delivery devices are not always available. We describe and bench test a method of delivering NO during MRI using standard equipment in which a NO delivery device was positioned in the MRI control room with the NO blender component connected to oxygen and set to 80 ppm and delivering flow via 12 m of tubing to a MRI-compatible ventilator, set up inside the MRI scanner magnet room.

METHODS

For our bench test, the ventilator was set up normally and connected to an infant test lung to simulate several patients of differing weight (ie, 4 kg, 10 kg, 20 kg). The NO blender delivered flows of 2-10 L/min to the ventilator to achieve a range of NO and oxygen concentrations monitored via extended tubing. The measured values were compared to calculated values.

RESULTS

A range of NO concentrations (12-41 ppm) and F_IO2 values (0.67-0.97) were achieved during the bench testing. The additional flow increased delivered peak inspiratory pressure and PEEP by 1-5 cm H₂O. Calculated values were within acceptable ranges and were used to create a lookup table.

CONCLUSIONS

In clinical use, this system can safely generate a range of NO flows of 15-42 ppm with an accompanying F_IO2 range of 0.34-0.98.

Effects of inhaled nitric oxide on haemodynamics and gas exchange in children after having undergone cardiac surgery utilising cardiopulmonary bypass

INTRODUCTION

For CHD patients undergoing corrective surgery utilising cardiopulmonary bypass, post-operative inhaled nitric oxide has been administered to alleviate pulmonary hypertension. We performed a systematic review and meta-analyses to determine the effect of inhaled nitric oxide on haemodynamics, gas exchange, and hospitalisation characteristics in children immediately after cardiopulmonary bypass.

MATERIALS AND METHODS

A systematic review of the literature was performed to identify full-text manuscripts in English. PubMed, EMBASE, and the Cochrane databases were queried. Once manuscripts were identified for inclusion, a list of all the endpoints in each manuscript was created. Endpoints with data present from two or more studies were then kept for pooled analyses. All endpoints included were continuous variables and so mean and standard deviation were utilised as the effect data for comparison.

RESULTS

A total of eight studies were deemed appropriate for inclusion. There were significant differences with decreases in mean pulmonary artery pressure of -6.82 mmHg, left atrial pressure of -1.16 mmHg, arteriovenous oxygen difference of -1.63, arterial carbon dioxide concentration of -2.41 mmHg, mechanical ventilation duration of -8.56 hours, and length of cardiac ICU stay duration of -0.91 days. All significant variables achieved p < 0.001.

CONCLUSION

Inhaled nitric oxide in children immediately after cardiopulmonary bypass decreases mean pulmonary artery pressure significantly and decreases the arterial carbon dioxide concentration significantly without significantly altering other haemodynamic parameters. This results in a statistically shorter duration of mechanical ventilation and cardiac ICU length of stay without altering overall hospital length of stay.

Postoperative Inhaled Nitric Oxide Does Not Decrease Length of Stay in Pediatric Cardiac Surgery Admissions

Pulmonary hypertension is one of the most challenging complications in congenital heart surgery. The purpose of this study was to characterize inhaled nitric oxide administration in children with and without pulmonary hypertension who underwent congenital heart surgery and to describe the effect of nitric oxide administration on admission outcomes. This is a cross-sectional study utilizing data from the Pediatric Health Information System (PHIS) and PHIS + databases from 2004 to 2015. Pediatric patients with a congenital heart disease diagnosis were included and divided into groups with pulmonary hypertension that received and not received inhaled nitric oxide and patients without diagnosis of pulmonary hypertension who received and did not receive inhaled nitric oxide. For all admissions, the following were captured: age of admission, gender, year of admission, length of stay, billed charges, inpatient mortality, the presence of specific congenital malformations of the heart, specific cardiac surgeries, and comorbidities. Comparisons between groups were completed using a Mann-Whitney-U test and Fisher's exact test. Outcomes evaluation was completed using univariate and regression analyses. A total of 40,194 pediatric cardiac surgical admissions without pulmonary hypertension were identified. Of these, 726 (1.8%) received inhaled nitric oxide. Regression analyses demonstrated that inhaled nitric oxide was independently associated with increased length of stay, billed charges, and inpatient mortality. A total of 1678 pediatric cardiac surgical admissions with pulmonary hypertension were identified. Of these, 195 (11.6%) received inhaled nitric oxide. Regression analyses demonstrated that inhaled nitric oxide was independently associated with a significant increase in length of stay and billed charges. There was no statistically significant association between inhaled nitric oxide and decrease mortality. Administration of inhaled nitric oxide after pediatric cardiac surgery increases length of stay and billed charges while not providing improved inpatient mortality. In fact, administration of inhaled nitric oxide was associated with increased mortality in those without pulmonary hypertension while not impacting mortality in any way in those with pulmonary hypertension.

Utilization of inhaled nitric oxide after surgical repair of truncus arteriosus: A multicenter analysis

BACKGROUND

Elevated pulmonary vascular resistance (PVR) is common following repair of truncus arteriosus. Inhaled nitric oxide (iNO) is an effective yet costly therapy that is frequently implemented postoperatively to manage elevated PVR.

OBJECTIVES

We aimed to describe practice patterns of iNO use in a multicenter cohort of patients who underwent repair of truncus arteriosus, a lesion in which recovery is often complicated by elevated PVR. We also sought to identify patient and center factors that were more commonly associated with the use of iNO in the postoperative period.

DESIGN

Retrospective cohort study.

SETTING

15 tertiary care pediatric referral centers.

PATIENTS

All infants who underwent definitive repair of truncus arteriosus without aortic arch obstruction between 2009 and 2016.

INTERVENTIONS

Descriptive statistics were used to demonstrate practice patterns of iNO use. Bivariate comparisons of characteristics of patients who did and did not receive iNO were performed, followed by multivariable mixed logistic regression analysis using backward elimination to identify independent predictors of iNO use.

MAIN RESULTS

We reviewed 216 patients who met inclusion criteria, of which 102 (46%) received iNO in the postoperative period: 69 (68%) had iNO started in the operating room and 33 (32%) had iNO initiated in the ICU. Median duration of iNO use was 4 days (range: 1-21 days). In multivariable mixed logistic regression analysis, use of deep hypothermic circulatory arrest (odds ratio: 3.2; 95% confidence interval: 1.2, 8.4) and center (analyzed as a random effect, p = .02) were independently associated with iNO use.

CONCLUSIONS

In this contemporary multicenter study, nearly half of patients who underwent repair of truncus arteriosus received iNO postoperatively. Use of iNO was more dependent on individual center practice rather than patient characteristics. The study suggests a need for collaborative quality initiatives to determine optimal criteria for utilization of this important but expensive therapy.

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.

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

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

Pediatric Perioperative Pulmonary Arterial Hypertension: A Case-Based Primer

The perioperative period is an extremely tenuous time for the pediatric patient with pulmonary arterial hypertension. This article will discuss a multidisciplinary approach to preoperative planning, the importance of early identification of pulmonary hypertensive crises, and practical strategies for postoperative management for this unique group of children.

Spectrum of Off-Label Nitric Oxide Utilization After Pediatric Cardiac Surgery Among Centers of Varying Surgical Volume

Objective:

Nitric oxide is utilized after pediatric cardiac surgery as an off-label medication without much evidence, is expensive, and varies among centers of varying surgical volume. The objective of our study was to describe the spectrum of nitric oxide utilization and to evaluate the effect of nitric oxide utilization on outcomes among patients cared for in centers of varying surgical volume using Pediatric Health Information system.

Methods:

Patients aged ≤18 years undergoing heart surgery were included (2004-2015). Multivariable mixed-effects logistic regression models were fitted to evaluate association of center volume with odds of nitric oxide utilization among patients undergoing heart operations. Centers were classified into 3 volume categories based on tertiles of number of cardiopulmonary bypass cases performed (low volume: 34 792 patients, 21 centers; medium volume: 38 362 patients, 13 centers; high volume: 30 560 patients, 7 centers).

Results:

A total of 103 714 patients from 41 hospitals were included. Of these, 15 708 (15.1%) patients received nitric oxide after cardiac surgery. Of the patients receiving nitric oxide, only 3936 (25.1%) patients were associated with a diagnosis of pulmonary hypertension. In adjusted models, low- and medium-volume centers were associated with higher nitric oxide utilization after heart operations as compared to high-volume centers (low vs high, odds ratio [OR]: 1.48, 95% confidence interval [CI]: 1.38-1.60; medium vs high, OR: 1.33, 95% CI: 1.26-1.41). Despite higher nitric oxide utilization, the mortality was worse among patients treated in low- and medium-volume centers, as compared to high-volume centers (low vs high, OR: 1.42, 95% CI: 1.26-1.60; medium vs high, OR: 1.14, 95% CI: 1.04-1.25).

Conclusions:

This study demonstrates variation in nitric oxide utilization after heart operations among centers of varying surgical volume. Further, it raises questions on the benefit of nitric oxide administration after pediatric cardiac surgery.

A Quality Improvement Initiative to Standardize Use of Inhaled Nitric Oxide in the PICU

Background:

Inhaled nitric oxide (iNO) is a potent pulmonary vasodilator used off-label to treat refractory hypoxemia in the pediatric intensive care unit (PICU). However, clinical practice varies widely, and there is limited evidence to support this expensive therapy. Our objective was to test whether implementation of a clinical guideline for iNO therapy would decrease practice variability, reduce ineffective iNO utilization, and control iNO-related costs.

Methods:

We used quality improvement (QI) methodology to standardize the use of iNO in a single quaternary care PICU (noncardiac). All PICU patients receiving iNO therapy between January 1, 2010, and December 31, 2013, were included. The QI intervention was the development and implementation of a clinical guideline for iNO initiation, continuation, and weaning. iNO use was monitored using statistical process control charts.

Results:

We derived baseline data from 30 preguideline patients (35 separate iNO courses) compared with 33 postguideline patients (36 separate iNO courses). Despite similar baseline characteristics, disease severity, and degree of hypoxemia, postguideline patients had a shorter median [interquartile range (IQR)] duration of iNO therapy than preguideline patients [76 (48–124) hours versus 162 (87–290) hours; P < 0.0001]. We have sustained the reduced iNO usage throughout the postguideline period. Postguideline patients also had improved provider documentation and a median iNO cost savings of $4,600.

Conclusions:

Implementation of iNO usage guidelines was associated with decreased iNO usage and cost of iNO therapy in the PICU.

Plasma asymmetric dimethylarginine levels are increased in neonates with bronchopulmonary dysplasia-associated pulmonary hypertension

OBJECTIVE

To test the hypothesis that levels of the endogenous inhibitor of nitric oxide production, asymmetric dimethylarginine (ADMA), would be greater in preterm infants with bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH) than in infants with BPD alone.

STUDY DESIGN

A case-control study of 23 patients with both BPD and PH (cases) and 95 patients with BPD but no evidence of PH (controls). Levels of ADMA were compared between cases and controls by t test.

RESULTS

Patients with both BPD and PH had greater plasma levels of ADMA than patients with BPD alone (P = .04). In samples drawn before 28 days of life, greater levels of ADMA were again found in cases compared with controls (P = .02). The plasma arginine-to-ADMA ratio was lower in cases than in controls (P = .03), suggesting a greater likelihood of inhibition of nitric oxide production in patients with both BPD and PH than in patients with BPD alone.

CONCLUSION

In this neonatal BPD cohort, ADMA levels are increased in patients with BPD who develop PH. We speculate that ADMA may be both a biomarker and a potential therapeutic target for preterm infants with BPD-associated PH.

Therapeutic effect of eNOS-transfected endothelial progenitor cells on hemodynamic pulmonary arterial hypertension

Hemodynamic pulmonary arterial hypertension (HPAH) is a common symptom in congenital heart disease (CHD) patients with a left-to-right shunt. Endothelial NO synthase (eNOS) and endothelial-like progenitor cells result in significant improvement of right ventricular systolic pressure in established pulmonary arterial hypertension (PAH) models. We hypothesized that bone marrow (BM)-derived endothelial progenitor cells (EPCs) and eNOS would prevent HPAH in a newly established rat model. The heNOS gene was cloned into a PSUCMV vector, and a high-titer adenovirus was generated. Mononuclear cells (MNCs) from rat BM were differentiated into EPCs by treatment with various cytokines, and a high purity of EPCs (>70%) was confirmed using the markers DiI ac-LDL, UEA-1, vWF and Flk-1. An ideal rat HPAH model was successfully established based on right lung lobectomy, and was confirmed by pressure measurement and histological staining. heNOS was successfully transfected into EPCs, which were then transplanted into HPAH rats. Two weeks after transplantation, the systolic pulmonary arterial blood pressure (sPAP) was significantly reduced by heNOS-EPCs treatment and by transplantation of control EPCs. The high number of muscular pulmonary arteries and the thickness of the muscular coat characteristic of HPAH rats were clearly reversed or even restored to normal levels following transplantation of EPCs, particularly eNOS-EPCs. These findings indicate a critical role of eNOS in HPAH treatment and suggest that eNOS-transfected EPCs may provide an effective strategy for HPAH treatment in CHD patients.

Arginine de novo and nitric oxide production in disease states

Arginine is derived from dietary protein intake, body protein breakdown, or endogenous de novo arginine production. The latter may be linked to the availability of citrulline, which is the immediate precursor of arginine and limiting factor for de novo arginine production. Arginine metabolism is highly compartmentalized due to the expression of the enzymes involved in arginine metabolism in various organs. A small fraction of arginine enters the NO synthase (NOS) pathway. Tetrahydrobiopterin (BH4) is an essential and rate-limiting cofactor for the production of NO. Depletion of BH4 in oxidative-stressed endothelial cells can result in so-called NOS3 "uncoupling," resulting in production of superoxide instead of NO. Moreover, distribution of arginine between intracellular transporters and arginine-converting enzymes, as well as between the arginine-converting and arginine-synthesizing enzymes, determines the metabolic fate of arginine. Alternatively, NO can be derived from conversion of nitrite. Reduced arginine availability stemming from reduced de novo production and elevated arginase activity have been reported in various conditions of acute and chronic stress, which are often characterized by increased NOS2 and reduced NOS3 activity. Cardiovascular and pulmonary disorders such as atherosclerosis, diabetes, hypercholesterolemia, ischemic heart disease, and hypertension are characterized by NOS3 uncoupling. Therapeutic applications to influence (de novo) arginine and NO metabolism aim at increasing substrate availability or at influencing the metabolic fate of specific pathways related to NO bioavailability and prevention of NOS3 uncoupling. These include supplementation of arginine or citrulline, provision of NO donors including inhaled NO and nitrite (sources), NOS3 modulating agents, or the targeting of endogenous NOS inhibitors like asymmetric dimethylarginine.

Pharmacotherapy for pulmonary hypertension

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

Therapeutic approaches using nitric oxide in infants and children

Pulmonary hypertension contributes significantly to the morbidity and mortality associated with many pediatric pulmonary and cardiac diseases. Nitric oxide, a gas molecule, is a unique pharmaceutical agent that can be inhaled and thus delivered directly to the lung. Inhaled nitric oxide was approved by the FDA in 1999 as a therapy for infants with persistent pulmonary hypertension. Since then, the use of inhaled nitric oxide has expanded to other neonatal and pediatric conditions, and our knowledge of its properties and mechanisms of action has increased tremendously. This review discusses the physiology of nitric oxide signaling, the most common indications for its clinical use, and promising new investigations that may enhance endogenous production of nitric oxide and/or improve vascular response to it.