Acta Paediatrica. 2020;109:930-934. wileyonlinelibrary.com/journal/apa | INTRODUC TI ONPulmonary hypertension (PH) complicating neonatal hypoxaemic respiratory failure occurs in approximately 0.4-6.8 cases per 1000 live births and is associated with significant morbidity and mortality. 1,2 The terms "pulmonary hypertension" and "persistent pulmonary hypertension of the newborn" (PPHN) are often used interchangeably, and this probably reflects the absence of clear case definitions.Unlike paediatric and adult pulmonary hypertension, there is no internationally accepted definition of PH in neonatal medicine. 3,4 The lack of a standardised definition precludes meaningful interpretation of clinical trials in this field, because it is difficult to compare trials with different entry criteria, perform subgroup analyses stratified by disease severity and adjust for confounding variables.Abbreviations: a/A ratio, alveolar to arterial oxygen tension ratio; BPD, bronchopulmonary dysplasia; iNO, inhaled nitric oxide; OI, oxygenation index; PAP, pulmonary arterial pressure; PH, pulmonary hypertension; PPHN, persistent pulmonary hypertension of the newborn; RCT, randomized controlled trial. Abstract Aim: Pulmonary hypertension (PH) frequently complicates neonatal hypoxaemic respiratory failure, but is inconsistently defined. We aimed to describe the variation among randomised controlled trials (RCTs) of inhaled nitric oxide (iNO), in relation to the definition of PH and/or hypoxaemic respiratory failure used to select patients for trial inclusion. Methods: PubMed, Cochrane Library and ClinicalTrials.gov were systematically searched for RCTs of iNO in neonates. Included studies were assessed for clinical and/or echocardiography criteria used to define PH/hypoxaemic respiratory failure. Results: Thirty-two trials were included in this review, of which 23 enrolled infants ≥34 weeks' gestation. Echocardiographic diagnosis was used in 21 studies, but there was considerable variation in the echocardiographic parameters used to diagnose PH. The most commonly used indices included markers of tricuspid regurgitation and extrapulmonary shunt. Conclusion: There is wide variation in the definition of PH used to select infants for inclusion into RCTs of iNO therapy in neonates. We recommend that an international consensus be reached on which parameters should be used and the thresholds defining severity of disease. K E Y W O R D S inhaled nitric oxide, neonatal, pulmonary hypertension, randomised controlled trial, systematic review This article is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland. | 931 HOYLE Et aL.Despite an absence of a clear definition of PH in this population, randomised controlled trials (RCTs) have frequently included neonates with hypoxaemic respiratory failure complicated by PH/ PPHN when evaluating the efficacy of pulmonary vasodilator therapies. Inhaled nitric oxide (iNO) is a licensed treatment for newborn infants ≥34 weeks gestation with hypoxic respiratory failure...

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