Inhaled nitric oxide in the premature infant: animal models and clinical experience

Novel scoring tool of hypoxemic respiratory failure and pulmonary hypertension for defining severity of persistent pulmonary hypertension of newborn

OBJECTIVE

To obtain preliminary validity data for a hypoxemic respiratory failure/pulmonary hypertension (HRF/PH) score for classifying persistent pulmonary hypertension of the newborn (PPHN).

STUDY DESIGN

Retrospective chart review of 100 consecutive neonates admitted to a Children's hospital from 2016-2021 with PPHN, gestational age ≥34 weeks, and echocardiograms in the first week. We assessed the correlation between HRF/PH score and short-term outcomes using linear and logistic regressions.

RESULTS

HRF/PH scores ranged 2-12 (mean 8.5), and were classified mild (0-5), moderate (6-10), and severe (11-15), with 6%, 77% and 17% infants in respective categories. HRF/PH score category correlated with invasive ventilation, nitric oxide, high frequency ventilation, vasoactive infusions, extracorporeal life support and death. HRF/PH score category did not correlate with duration of support or length of stay.

CONCLUSION

The HRF/PH score offers a promising representation of disease severity for PPHN. The tool requires further validation in prospective studies and evaluation for long-term outcomes.

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.

A pilot study on the kinetics of metabolites and microvascular cutaneous effects of nitric oxide inhalation in healthy volunteers

RATIONALE

Inhaled nitric oxide (NO) exerts a variety of effects through metabolites and these play an important role in regulation of hemodynamics in the body. A detailed investigation into the generation of these metabolites has been overlooked.

OBJECTIVES

We investigated the kinetics of nitrite and S-nitrosothiol-hemoglobin (SNO-Hb) in plasma derived from inhaled NO subjects and how this modifies the cutaneous microvascular response.

FINDINGS

We enrolled 15 healthy volunteers. Plasma nitrite levels at baseline and during NO inhalation (15 minutes at 40 ppm) were 102 (86-118) and 114 (87-129) nM, respectively. The nitrite peak occurred at 5 minutes of discontinuing NO (131 (104-170) nM). Plasma nitrate levels were not significantly different during the study. SNO-Hb molar ratio levels at baseline and during NO inhalation were 4.7E-3 (2.5E-3-5.8E-3) and 7.8E-3 (4.1E-3-13.0E-3), respectively. Levels of SNO-Hb continued to climb up to the last study time point (30 min: 10.6E-3 (5.3E-3-15.5E-3)). The response to acetylcholine iontophoresis both before and during NO inhalation was inversely associated with the SNO-Hb level (r: -0.57, p = 0.03, and r: -0.54, p = 0.04, respectively).

CONCLUSIONS

Both nitrite and SNO-Hb increase during NO inhalation. Nitrite increases first, followed by a more sustained increase in Hb-SNO. Nitrite and Hb-SNO could be a mobile reservoir of NO with potential implications on the systemic microvasculature.

Pathophysiological mechanism of long-term noninvasive ventilation in stable hypercapnic patients with COPD using functional respiratory imaging

Introduction

Patients with severe COPD often develop chronic hypercapnic respiratory failure. Their prognosis worsens and they are more likely to develop exacerbations. This has major influence on the health-related quality of life. Currently, there is no information about the success of long-term noninvasive ventilation (NIV) among patients who receive NIV in acute settings. Also, little is known about the pathophysiological mechanism of NIV.

Methods

Ten Global Initiative for Obstructive Lung Disease stage III and IV COPD patients with respiratory failure who were hospitalized following acute exacerbation were treated with NIV using a Synchrony BiPAP device for 6 months. Arterial blood gases and lung function parameters were measured. Low-dose computed tomography of the thorax was performed and used for segmentation. Further analyses provided lobe volume, airway volume, and airway resistance, giving an overall functional description of the separate airways and lobes. Ventilation perfusion (VQ) was calculated. Patient-reported outcomes were evaluated.

Results

PaCO₂ significantly improved from 50.03 mmHg at baseline to 44.75 mmHg after 1 month and 43.37 mmHg after 6 months (P=0.006). Subjects showed improvement in the 6-minute walk tests (6MWTs) by an average of 51 m (from 332 m at baseline to 359 m at 1 month and 383 m at 6 months). Patients demonstrated improvement in self-reported anxiety (P=0.018). The improvement in image-based VQ was positively associated with the 6MWT and the anxiety domain of the Severe Respiratory Insufficiency Questionnaire.

Conclusion

Though previous studies of long-term NIV have shown conflicting results, this study demonstrates that patients can benefit from long-term NIV treatment, resulting in improved VQ, gas exchange, and exercise tolerance.

Pulmonary vascular effects of pulsed inhaled nitric oxide in COPD patients with pulmonary hypertension

Introduction

Severe chronic obstructive pulmonary disease (COPD) is often associated with secondary pulmonary hypertension (PH), which worsens prognosis. PH can be lowered by oxygen, but also by inhaled nitric oxide (NO), which has the potential to improve the health status of these patients. NO is an important mediator in vascular reactions in the pulmonary circulation. Oral compounds can act through NO-mediated pathways, but delivering pulsed inhaled NO (iNO) directly to the airways and pulmonary vasculature could equally benefit patients. Therefore, a proof-of-concept study was performed to quantify pulmonary blood vessel caliber changes after iNO administration using computed tomography (CT)-based functional respiratory imaging (FRI).

Methods

Six patients with secondary PH due to COPD received “pulsed” iNO in combination with oxygen for 20 minutes via a nasal cannula. Patients underwent a high-resolution CT scan with contrast before and after iNO. Using FRI, changes in volumes of blood vessels and associated lobes were quantified. Oxygen saturation and blood pressure were monitored and patients were asked about their subjective feelings.

Results

Pulmonary blood vessel volume increased by 7.06%±5.37% after iNO. A strong correlation (Ω²₀=0.32, P=0.002) was obtained between ventilation and observed vasodilation, suggesting that using the pulsed system, iNO is directed toward the ventilated zones, which consequently experience more vasodilation. Patients did not develop oxygen desaturation, remained normotensive, and perceived an improvement in their dyspnea sensation.

Conclusion

Inhalation of pulsed NO with oxygen causes vasodilation in the pulmonary circulation of COPD patients, mainly in the well-ventilated areas. A high degree of heterogeneity was found in the level of vasodilation. Patients tend to feel better after the treatment. Chronic use trials are warranted.

Inhaled Nitric Oxide as an Adjunctive Treatment for Cerebral Malaria in Children: A Phase II Randomized Open-Label Clinical Trial

Treatment with inhaled nitric oxide as an adjuvant therapy for pediatric patients with cerebral malaria for 48 hours did not result in a significant difference in plasma Angiopoietin-1 levels when compared with placebo in a phase II open-label clinical trial.

Background. Children with cerebral malaria (CM) have high rates of mortality and neurologic sequelae. Nitric oxide (NO) metabolite levels in plasma and urine are reduced in CM.

Methods. This randomized trial assessed the efficacy of inhaled NO versus nitrogen (N₂) as an adjunctive treatment for CM patients receiving intravenous artesunate. We hypothesized that patients treated with NO would have a greater increase of the malaria biomarker, plasma angiopoietin-1 (Ang-1) after 48 hours of treatment.

Results. Ninety-two children with CM were randomized to receive either inhaled 80 part per million NO or N₂ for 48 or more hours. Plasma Ang-1 levels increased in both treatment groups, but there was no difference between the groups at 48 hours (P = not significant [NS]). Plasma Ang-2 and cytokine levels (tumor necrosis factor-α, interferon-γ, interleukin [IL]-1β, IL-6, IL-10, and monocyte chemoattractant protein-1) decreased between inclusion and 48 hours in both treatment groups, but there was no difference between the groups (P = NS). Nitric oxide metabolite levels—blood methemoglobin and plasma nitrate—increased in patients treated with NO (both P < .05). Seven patients in the N₂ group and 4 patients in the NO group died. Five patients in the N₂ group and 6 in the NO group had neurological sequelae at hospital discharge.

Conclusions. Breathing NO as an adjunctive treatment for CM for a minimum of 48 hours was safe, increased blood methemoglobin and plasma nitrate levels, but did not result in a greater increase of plasma Ang-1 levels at 48 hours.

Inhaled nitric oxide for preterm neonates

The evidence for the benefits of inhaled nitric oxide (iNO) on gas exchange, cytokine-induced lung inflammation, and vascular dysfunction has been demonstrated by several animal and human studies. The use of iNO in extremely low birth weight neonates for the prevention of adverse outcomes like chronic lung disease and neurologic injury has been investigated, but the findings remain inconclusive. This review briefly outlines the biologic rationale for the use of iNO in preterm neonates and the results on the outcome measures of bronchopulmonary dysplasia and brain injury from the recent clinical trials. This article focuses on the potential toxicities, persistent controversies, and unanswered questions regarding the use of this treatment modality in this patient population at high risk for adverse outcomes.

Inhaled NO as a therapeutic agent

In 1991, Frostell and colleagues reported that breathing low concentrations of nitric oxide (NO) decreased pulmonary artery pressure (PAP) in awake lambs with experimental pulmonary hypertension (PH) [Frostell C, Fratacci MD, Wain JC, Jones R, Zapol WM. Inhaled nitric oxide. A selective pulmonary vasodilator reversing hypoxic pulmonary vasoconstriction. Circulation 1991;83:2038-47]. Subsequently, efforts of multiple research groups studying animals and patients led to approval of inhaled NO by the US Food and Drug Administration in 1999 and the European Medicine Evaluation Agency and European Commission in 2001. Inhaled NO is currently indicated for the treatment of term and near-term neonates with hypoxemia and PH. Since regulatory approval, several studies have suggested that NO inhalation can prevent chronic lung disease in premature infants. In addition, unanticipated systemic effects of inhaled NO may lead to treatments for a variety of disorders including ischemia-reperfusion injury. This review summarizes the pharmacology and physiological effects of breathing NO. The application of inhaled NO to hypoxemic neonates with PH is discussed including recent studies exploring the use of inhaled NO to prevent bronchopulmonary dysplasia in premature infants. This review also highlights the application of inhaled NO to treat adults with cardiopulmonary disease, strategies to augment the efficacy of inhaled NO, and potential applications of the systemic effects of the gas.

Outcome of premature infants delivered after prolonged premature rupture of membranes before 25 weeks of gestation

OBJECTIVE

To identify factors influencing the outcome of premature infants delivered after prolonged premature rupture of membranes before 25 weeks' gestation.

DESIGN AND POPULATION

All premature infants with gestational age <34 weeks, either inborn or outborn, with history of rupture of membranes before 25 weeks' gestation, admitted to our NICU between January 1992 and July 1997, were eligible for this retrospective study. Collected information included birth weight, gestational age at rupture of membranes and at delivery, duration between rupture of membranes and delivery (latency period), severity of oligohydramnios, pre- and post-natal managements, and follow-up of survivors.

RESULTS

A total of 28 neonates fulfilled the inclusion criteria. Despite new strategies of ventilation and optimal management, the overall mortality rate was 43% (12/28). Nonsurvivors were significantly less mature at rupture of membranes, and had severe oligohydramnios (anamnios). We also noted less antenatal corticosteroids and antibiotic therapy in this group. Nine of eleven infants (82%) following rupture of membranes before 22 weeks' gestation died shortly after birth. The two remaining infants developed severe bronchopulmonary dysplasia. Nine deaths occurred in thirteen cases (69%) of anamnios. The major death causes were refractory respiratory failure and neurologic complications. Half of all survivors (8/16) developed bronchopulmonary dysplasia.

CONCLUSION

The outcome of premature infants following prolonged premature rupture of membranes before 25 weeks' gestation is influenced by gestational age at rupture, severity of oligohydramnios, and antenatal antibiotics and corticosteroids. Neonates with rupture of membranes before 22 weeks have a very low chance of survival at the present time.

Inhaled nitric oxide in premature neonates with severe hypoxaemic respiratory failure: a randomised controlled trial

BACKGROUND

Inhaled nitric oxide improves oxygenation and lessens the need for extracorporeal-membrane oxygenation in full-term neonates with hypoxaemic respiratory failure and persistent pulmonary hypertension, but potential adverse effects are intracranial haemorrhage and chronic lung disease. We investigated whether low-dose inhaled nitric oxide would improve survival in premature neonates with unresponsive severe hypoxaemic respiratory failure, and would not increase the frequency or severity of intracranial haemorrhage or chronic lung disease.

METHODS

We did a double-blind, randomised controlled trial in 12 perinatal centres that provide tertiary care. 80 premature neonates (gestational age < or = 34 weeks) with severe hypoxaemic respiratory failure were randomly assigned inhaled nitric oxide (n=48) or no nitric oxide (n=32, controls). Our primary outcome was survival to discharge. Analysis was by intention to treat. We studied also the rate and severity of intracranial haemorrhage, pulmonary haemorrhage, duration of ventilation, and chronic lung disease at 36 weeks' postconceptional age.

FINDINGS

The two groups did not differ for baseline characteristics or severity of disease. Inhaled nitric oxide improved oxygenation after 60 min (p=0.03). Survival at discharge was 52% in the inhaled-nitric-oxide group and 47% in controls (p=0.65). Causes of death were mainly related to extreme prematurity and were similar in the two groups. The two groups did not differ for adverse events or outcomes (intracranial haemorrhage grade 2-4, 28% inhaled nitric oxide and 33% control; pulmonary haemorrhage 13% and 9%; chronic lung disease 60% and 80%).

INTERPRETATION

Low-dose inhaled nitric oxide improved oxygenation but did not improve survival in severely hypoxaemic premature neonates. Low-dose nitric oxide in the most critically ill premature neonates does not increase the risk of intracranial haemorrhage, and may decrease risk of chronic lung injury.