Inhaled nitric oxide works through an elegant piece of human physiology. Nitric oxide is a naturally produced signaling molecule that relaxes the smooth muscle lining blood vessels. When delivered through a ventilator circuit into the lungs, it acts as a selective pulmonary vasodilator, opening up the tiny vessels of the lung’s circulation precisely where air is reaching, and thereby redirecting blood toward regions that can actually exchange oxygen and carbon dioxide. In term and near-term newborns with hypoxemic respiratory failure driven by persistent pulmonary hypertension, a condition in which the lung vessels remain constricted and blood bypasses the lungs through fetal shunts, this mechanism produces dramatic improvements in oxygenation and has been shown in randomized trials to reduce the need for extracorporeal membrane oxygenation and to lower mortality. That success earned the drug its regulatory approval and made it a cornerstone of neonatal intensive care for mature infants.

Preterm infants, however, are a fundamentally different physiological challenge. In babies born at or before 34 weeks, severe hypoxemia rarely stems from a single, reversible vascular problem. Their lungs are structurally immature, often underdeveloped, and frequently damaged by the very treatments that keep them alive, including mechanical ventilation and oxygen exposure. Pulmonary hypertension in these infants can arise from multiple distinct mechanisms: maladaptation of the pulmonary vasculature, hypoplastic lungs caused by conditions such as oligohydramnios and prolonged rupture of membranes, or the evolving vascular remodeling that precedes bronchopulmonary dysplasia, the chronic lung disease of prematurity. Because the underlying biology is so heterogeneous, a therapy that dilates vessels may help some infants dramatically while doing nothing, or even harm, in others. This biological complexity is precisely why the evidence for inhaled nitric oxide in preterm babies has been inconsistent for more than two decades, with large randomized trials and individual-patient-data meta-analyses failing to demonstrate a survival advantage.

To bring clarity to this contested field, the Colombian research team conducted a systematic review following the PRISMA 2020 reporting guidelines, searching the major biomedical databases for studies published up to October 11, 2025. They included both observational studies and clinical trials that reported mortality among preterm infants with early hypoxemic respiratory failure treated with inhaled nitric oxide. Nineteen studies met the criteria for the qualitative synthesis, and six of them, encompassing a total of 556 infants, provided data suitable for quantitative pooling in a random-effects meta-analysis. The methodological quality of the included studies ranged from poor to good, and the authors were candid about the limitations, which centered on confounding, the persistent problem that sicker babies are more likely to receive the drug, and on statistical heterogeneity across studies.

The headline result was stark in its uncertainty. When the six pooled studies were combined, infants treated with inhaled nitric oxide showed no statistically significant reduction in mortality compared with those receiving standard care. The pooled relative risk was 0.65, with a 95 percent confidence interval spanning 0.29 to 1.48, an interval that comfortably includes the possibility of no effect at all, and even cannot exclude a substantial increase in risk. The I-squared statistic of 55.7 percent indicated moderate heterogeneity, meaning the individual studies disagreed with one another to a degree that complicates any single summary estimate. Importantly, the authors noted that infants who received the drug were more severely ill at baseline, a classic confounding by indication that biases observational comparisons against the treatment and makes the true effect even harder to pin down.

Yet the review’s most clinically valuable contribution may lie beyond the pooled mortality figure. The authors found that a positive oxygenation response, meaning a measurable improvement in blood oxygen levels after starting the gas, was associated with improved outcomes. In other words, the babies who respond to the drug are the babies who tend to do better, which reframes the question from whether the therapy works to which infants it works for. The magnitude and value of that response varied systematically by several clinical characteristics: gestational age, the timing of pulmonary hypertension onset, whether the diagnosis was confirmed by echocardiography, and the severity of the hypoxemia itself. These variables effectively define phenotypes, distinct clinical subgroups within the broad category of preterm respiratory failure, and the evidence suggests that treatment effect is not uniform across them.

This phenotype-driven framing aligns with a broader movement in neonatology toward precision medicine for premature lung disease. Recent work on the pulmonary vascular phenotypes of prematurity has argued that lumping all hypoxemic preterm infants together in trials guarantees diluted, uninterpretable results, because the population mixes infants whose pulmonary hypertension is transient and reversible with those whose lung disease is structural and irreversible. It also echoes findings from studies of specific subgroups, such as infants with pulmonary hypoplasia following extreme preterm premature rupture of membranes, where early functional echocardiography has been used to identify candidates likely to benefit from the therapy. A recent masked randomized controlled trial of early inhaled nitric oxide in extremely preterm infants with pulmonary hypertension, published in 2025, further underscores that the field is actively testing selective strategies rather than universal ones.

The practical implications for intensive care units are significant. In many countries, inhaled nitric oxide is expensive, requires specialized delivery equipment and monitoring, and carries known risks, including potential effects on bleeding and platelet function, which are particular concerns in fragile preterm infants vulnerable to intraventricular hemorrhage. If the therapy does not reduce mortality across the board in this population, then routine or reflexive use cannot be justified on survival grounds alone, and clinicians must weigh the costs and risks against the possibility of benefit in carefully selected patients. The review’s authors explicitly argue for a selective, phenotype-driven approach rather than routine administration to all preterm infants with hypoxemic respiratory failure, a position that is likely to inform upcoming updates to clinical guidelines, including the European consensus guidelines on the management of respiratory distress syndrome.

What the review cannot do, and the authors are careful to acknowledge this, is settle the question definitively. The evidence base remains thin: only 556 infants entered the quantitative synthesis, the studies were largely observational, and the quality limitations related to confounding and heterogeneity mean the confidence interval is wide enough to accommodate clinically meaningful benefit or harm. The authors call for well-designed randomized trials in this high-risk population, ideally ones that stratify enrollment by the very characteristics their analysis identified as effect modifiers, such as echocardiographically confirmed pulmonary hypertension and early versus late onset of disease. Until such trials are completed, the pooled estimate of a 35 percent relative reduction in risk that fails to reach statistical significance should be read not as proof of futility, but as a signal that any benefit, if it exists, is confined to identifiable subgroups.

For the families of the roughly one in ten babies born preterm worldwide, the message is one of cautious realism rather than despair. Inhaled nitric oxide remains a powerful and appropriate tool for term and near-term newborns with pulmonary hypertension, and it may still have a role for selected preterm infants whose physiology matches the responder profile. What this meticulous synthesis makes clear is that the era of one-size-fits-all rescue therapy for the smallest patients is ending, replaced by a harder but more honest question: not whether the drug works, but for whom, when, and how clinicians can tell the difference at the bedside before the first dose is given.

Subject of Research: Effectiveness of inhaled nitric oxide for reducing mortality in preterm newborns with early hypoxemic respiratory failure

Article Title: Impact on mortality of inhaled nitric oxide in newborns ≤34 weeks with early hypoxemic respiratory failure: systematic review and meta-analysis

Article References: Alvarado-Socarras, J. L., Theurel-Martín, D. E., & Manrique-Hernández, E. F. (2026). Impact on mortality of inhaled nitric oxide in newborns ≤34 weeks with early hypoxemic respiratory failure: systematic review and meta-analysis. Pediatric Research. https://doi.org/10.1038/s41390-026-05564-6

Image Credits: AI Generated

DOI: 10.1038/s41390-026-05564-6

Keywords: inhaled nitric oxide, preterm infants, hypoxemic respiratory failure, pulmonary hypertension, neonatology, systematic review, meta-analysis, mortality, bronchopulmonary dysplasia, oxygenation response, gestational age, precision medicine

The central tension the authors describe is physiological rather than technological. Positive airway pressure can recruit collapsed alveoli and raise lung volumes, improving oxygenation through positive end-expiratory pressure, or PEEP. In patients with hydrostatic pulmonary edema and left ventricular failure, PEEP may even improve cardiac output by reducing both afterload and preload. But in ARDS, respiratory drive is often markedly increased, fueled by cortical and peripheral inputs, mechanoreceptor stimulation, and inflammatory mediators. The result can be excessive spontaneous breathing effort, generating large negative pleural pressure swings, elevated transpulmonary pressures, and amplified regional lung stress. This phenomenon, known as patient self-inflicted lung injury, or P-SILI, can promote overdistension and the same barotrauma, volutrauma, and atelectrauma classically associated with ventilator-induced lung injury—particularly in the reduced, non-uniform ‘baby lung’ that characterizes ARDS.

The evidence linking injurious effort to outcomes is concrete. In acute hypoxemic respiratory failure, persistent high inspiratory effort under non-invasive ventilation, measured by esophageal pressure swings, has been shown to predict non-invasive ventilation failure. Large tidal volumes above 9 milliliters per kilogram of predicted body weight—reflecting the combination of delivered pressure support and strong patient effort—have likewise been associated with poor outcomes. Despite this, standardized bedside assessment of inspiratory effort, particularly using esophageal pressure monitoring, remains limited and is not routinely implemented in intensive care units. The authors argue that this monitoring gap is one of the key obstacles to using non-invasive support safely, because clinicians currently lack a reliable, widely available way to distinguish patients whose spontaneous breathing is helping them from those whose breathing is injuring them.

Interface choice matters enormously in this calculus. Helmet non-invasive ventilation enables delivery of higher PEEP levels with minimal air leaks, and patient-ventilator asynchronies are generally less clinically relevant than with face masks. Even when a patient’s inspiratory effort fails to trigger pressure support, the patient continues to perform genuine inspiratory work by drawing airflow and volume from the helmet—true work of breathing rather than an isometric effort. Intriguingly, the helmet’s longer trigger delays and less efficient pressurization may induce desynchronization that limits excessive transpulmonary pressure swings and potentially enhances lung protection. The trade-off is monitoring: tracking tidal volumes through a helmet remains challenging, and the interface can provoke claustrophobia. Face masks, by contrast, struggle to maintain a seal in edentulous patients, those with beards, or individuals with nasogastric tubes.

The clinical evidence for non-invasive ventilation and CPAP in ARDS remains inconsistent and highly dependent on disease severity. Some studies and subgroup analyses suggest these modalities may be feasible in carefully selected patients with mild ARDS who lack hemodynamic instability and retain preserved mental status, potentially avoiding intubation. Helmet-delivered non-invasive ventilation was specifically found to reduce intubation compared with high-flow nasal cannula in patients with COVID-19. Ongoing randomized trials—including HENIVOT-2, HighCPAP, and HONOUR—are expected to clarify the role of these approaches further. In the meantime, the authors outline reasonable starting settings: PEEP of approximately 5 centimeters of water, up to 10, with pressure support of 5 to 8 centimeters of water above PEEP, rapidly titrated according to comfort, effort, tidal volume, and gas exchange. Patients with persistent hypoxemia may require higher PEEP of 8 to 12 centimeters of water via helmet.

High-flow nasal cannula occupies a different niche. Delivering heated, humidified oxygen at 30 to 60 liters per minute, it reduces nasopharyngeal dead space, generates a modest PEEP effect through resistance to expiratory flow, and limits entrainment of ambient air, producing more stable alveolar oxygen delivery. These effects decrease work of breathing compared with standard oxygen, reflected in reduced respiratory rate, less dyspnea, and improved comfort. Compared with non-invasive ventilation, however, it provides lower PEEP and less homogeneous tidal volume distribution, as assessed by electrical impedance tomography. Its practical advantages are considerable: it imposes no uncomfortable interface, does not require sedation, and allows patients to remain awake, eat, speak, and undergo prone positioning.

The trial evidence favors high-flow therapy as a first-line strategy for moderate disease. Randomized trials in acute hypoxemic respiratory failure report lower intubation rates compared with conventional oxygen or non-invasive ventilation, particularly in patients with a PaO2/FiO2 ratio below 200 millimeters of mercury, although the effect on mortality remains uncertain. Current guidelines, including French consensus recommendations developed by the DELPHI method, recommend high-flow nasal cannula as first-line oxygen therapy in acute hypoxemic respiratory failure at that severity threshold. Typical initiation involves flows of 40 to 60 liters per minute, commonly 50, with the fraction of inspired oxygen adjusted to maintain target saturation and flow subsequently tuned to the patient’s inspiratory demand and work of breathing. The authors conclude that high-flow therapy should be considered first-line non-invasive support for most patients with moderate ARDS, provided close physiologic reassessment identifies failure early enough to avoid delayed intubation.

Deciding between a non-invasive trial and immediate intubation rests on a defined set of red flags. Severe hypoxemia, hemodynamic instability, additional organ failure such as renal failure or delirium, impending cardiac or respiratory arrest, coma, inability to protect the airway, a large secretion burden, or poor tolerance of interfaces should all prompt consideration of upfront intubation. When none of these is present, clinicians should assess the severity of hypoxemia alongside respiratory drive and inspiratory effort. Marked accessory muscle use and persistent signs of high work of breathing signal P-SILI risk. A reasonable sequence is a trial of high-flow nasal cannula with rapid reassessment of oxygenation, respiratory rate, and accessory muscle response, escalating to non-invasive ventilation if symptoms persist—while vigilantly avoiding high tidal volumes. Hypercapnia or respiratory acidosis may favor non-invasive ventilation with pressure support, but should also lower the threshold for intubation if it worsens.

Timing of intubation is the field’s most persistent dilemma. Delayed intubation has been identified as a risk factor for mortality in several studies, yet no trial has directly compared intubation versus no intubation in acute hypoxemic respiratory failure. Instead, randomized studies have used prespecified intubation criteria without demonstrating differences in time to intubation across oxygenation strategies. The French consensus identifies cardiac or respiratory arrest from hypoxemia and persistent hypoxemia despite maximal oxygen strategy—PaO2/FiO2 below 60 millimeters of mercury or oxygen saturation below 88 percent—as major criteria for intubation, alongside shock, worsening respiratory failure with tachypnea above 30 breaths per minute, recurrent desaturation, respiratory acidosis, or declining consciousness. The ROX index, which divides the ratio of oxygen saturation to inspired oxygen fraction by respiratory rate, is the best-validated bedside tool for predicting high-flow therapy failure and should complement, rather than replace, clinical judgment.

Awake prone positioning, widely adopted during the COVID-19 pandemic as an adjunct to high-flow therapy or non-invasive ventilation, adds another physiological lever. By improving ventilation-perfusion matching, promoting dorsal recruitment, and reducing dependent atelectasis, it reduced intubation rates when adherence was successfully achieved, though no mortality benefit was demonstrated. For non-COVID ARDS, the physiological rationale is plausible but the evidence remains insufficient. The review’s overarching message is that no single device should be applied for a fixed duration; instead, matching must be individualized to a patient’s evolving physiology. Non-invasive supports are valuable early in ARDS, but their safe use depends on careful selection, close physiologic monitoring, and timely recognition of failure. The next frontier, the authors argue, lies in phenotype-driven strategies and objective markers of injurious respiratory effort that can guide escalation decisions with far greater precision than today’s clinical gestalt.

Subject of Research: Physiology-guided use of non-invasive respiratory support, including high-flow nasal cannula and non-invasive ventilation, in acute respiratory distress syndrome

Article Title: Non-invasive respiratory supports in ARDS: Physiology-guided use, pitfalls, and pathways to success

Article References: Munshi, L., Antonelli, M., & Frat, J.-P. (2026). Non-invasive respiratory supports in ARDS: Physiology-guided use, pitfalls, and pathways to success. Intensive Care Medicine. https://doi.org/10.1007/s00134-026-08616-x

Image Credits: AI Generated

DOI: 10.1007/s00134-026-08616-x

Keywords: ARDS, non-invasive ventilation, high-flow nasal cannula, CPAP, P-SILI, PEEP, helmet ventilation, intubation, ROX index, acute hypoxemic respiratory failure, awake prone positioning, critical care