Article Text

Original research
Increase in the use of inhaled nitric oxide in neonatal intensive care units in England: a retrospective population study
  1. Nimish V Subhedar1,
  2. Sena Jawad2,
  3. Kayleigh Oughham2,
  4. Chris Gale3,
  5. Cheryl Battersby3
  6. UK Neonatal Collaborative
    1. 1Neonatal Intensive care Unit, Liverpool Women's Hospital, Liverpool, UK
    2. 2Neonatal Data Analysis Unit, Imperial College London, London, UK
    3. 3Neonatal Medicine, Imperial College London Faculty of Medicine, London, UK
    1. Correspondence to Dr Cheryl Battersby; c.battersby{at}


    Objective To describe temporal changes in inhaled nitric oxide (iNO) use in English neonatal units between 2010 and 2015.

    Design Retrospective analysis using data extracted from the National Neonatal Research Database.

    Setting All National Health Service neonatal units in England.

    Patients Infants of all gestational ages born 2010–2015 admitted to a neonatal unit and received intensive care.

    Main outcome measures Proportion of infants who received iNO; age at initiation and duration of iNO use.

    Results 4.9% (6346/129 883) of infants received iNO; 31% (1959/6346) were born <29 weeks, 18% (1152/6346) 29–33 weeks and 51% (3235/6346)>34 weeks of gestation. Between epoch 1 (2010–2011) and epoch 3 (2014–2015), there was (1) an increase in the proportion of infants receiving iNO: <29 weeks (4.9% vs 15.9%); 29–33 weeks (1.1% vs 4.8%); >34 weeks (4.5% vs 5.0%), (2) increase in postnatal age at iNO initiation: <29 weeks 10 days vs 18 days; 29–33 weeks 2 days vs 10 days, (iii) reduction in iNO duration: <29 weeks (3 days vs 2 days); 29–33 weeks (2 days vs 1 day).

    Conclusions Between 2010 and 2015, there was an increase in the use of iNO among infants admitted to English neonatal units. This was most notable among the most premature infants with an almost fourfold increase. Given the cost of iNO therapy, limited evidence of efficacy in preterm infants and potential for harm, we suggest that exposure to iNO should be limited, ideally to infants included in research studies (either observational or randomised placebo-controlled trial) or within a protocolised pathway. Development of consensus guidelines may also help standardise practice.

    • neonatology
    • epidemiology

    This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See:

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    What is known about the subject?

    • Inhaled nitric oxide (iNO) is a well-established and licensed therapy in term and near-term infants with hypoxaemic respiratory failure and pulmonary hypertension.

    • Evidence for the safety and efficacy of iNO in preterm infants is lacking.

    • iNO use is highly variable internationally; data describing iNO use across neonatal units in the UK are lacking.

    What this study adds?

    • Use of inhaled nitric oxide (iNO) increased over time from 3.4% (1293/37 885) in 2010–2011 to 6.4% (3112/48 838) in 2014–2015.

    • Increase in iNO use is most notable in the most preterm infants born <29 weeks for which there is a paucity of evidence of benefit.

    • There is a wide variation in iNO usage between neonatal intensive care units in England.


    Inhaled nitric oxide (iNO) is widely used in the treatment of hypoxaemic respiratory failure and persistent pulmonary hypertension of the newborn (PPHN). Although a well-established therapy in term and near-term infants with these conditions, the off-label use of iNO in preterm infants <34 weeks of gestation remains controversial. Population-based data indicate that there is wide variation in administration rates among US hospitals, but there are no equivalent data from the UK or mainland Europe.1–4 Data from individual centres and multicentre studies suggest that the use of iNO is increasing,2–5 especially in preterm infants, despite the lack of evidence of benefit in this population.

    We aimed to describe temporal changes in the use of iNO in neonates admitted to neonatal units in England using national data routinely recorded during clinical care and held in the National Neonatal Research database (NNRD). Our objectives were to (1) describe the proportion and characteristics of preterm and term infants who receive iNO between 2010 and 2015 and (2) determine whether there is variation in iNO use across tertiary level neonatal units and over time between 2010 and 2015.


    Setting, study design and data source

    This retrospective cohort study used routinely recorded, deidentified data held in the NNRD. The NNRD has complete coverage of infants admitted for neonatal care at a National Health Service neonatal unit in England, Scotland and Wales. The NNRD is formed from data extracted from neonatal electronic health record systems used by health professionals during routine clinical care. A defined data extract comprising approximately 450 items,6 the Neonatal Data Set, is transmitted quarterly to the Neonatal Data Analysis Unit at Imperial College London where data are cleaned and entered into the NNRD. High completeness and accuracy (>95%) of data held in the NNRD have been confirmed by a formal comparison with those recorded in case record forms of a multicentre, randomised placebo-controlled trial (RCT).7 Neonatal units in England contributing data to the NNRD consented for their unit data to be included in the study.

    Study population and data extraction

    We included data from infants who required any neonatal intensive care (defined using British Association of Perinatal Medicine categories of care 2011,8 primarily as needing mechanical ventilation or noninvasive ventilation plus parenteral nutrition) over a 6-year period, 01 January 2010 to 31 December 2015 in England. Infants who did not receive intensive care on a neonatal unit or who were not cared completely in units in Wales and Scotland were excluded from the analysis.

    We extracted daily variables (receipt of iNO, surfactant), demographic variables (birth weight, sex, gestational age), maternal factors (prolonged rupture of membranes >24 hours), diagnoses and survival to neonatal unit discharge. See online supplemental file 1 for diagnostic codes.

    Supplemental material


    The primary outcome was the rate of iNO use as a proportion of infants who received neonatal intensive care, unit level.

    The following secondary outcomes were analysed for infants who received iNO:

    • Timing of iNO initiation (postnatal age in days).

    • Duration of iNO.

    • Diagnoses including respiratory distress syndrome, persistent pulmonary hypertension of the newborn, pulmonary hypoplasia, congenital pneumonia, congenital diaphragmatic hernia, congenital heart disease, meconium aspiration syndrome (among infants ≥34 weeks of gestation).

    • Survival to neonatal unit discharge.

    Statistical analyses

    We describe the cohort at two levels: (1) at the level of the population of infants who received at least 1 day of neonatal intensive care and (2) at the level of the neonatal unit. For all outcomes, separate analyses were conducted by a priori defined gestational age bands: (a) extremely preterm (<29 weeks of gestation), (b) moderately preterm (29–33 weeks of gestation) and (c) late preterm/term (>34 weeks of gestation).

    Results are presented using medians (interquartile ranges) and percentages for continuous and categorical variables, respectively.

    For the neonatal unit-level analysis, we limited this to the 47 tertiary neonatal units in England who have treated five or more infants with nitric oxide. For this analysis, we attributed iNO use to the first unit providing iNO therapy regardless of whether an infant was treated with iNO in more than one neonatal unit. The total number of neonatal units in England during this period decreased from 169 (in 2010–2011) to 161 (in 2014–2015); this reflects the merger or closure of units. Rates of iNO use across tertiary units are presented graphically without comparative testing.

    Patient and public involvement

    Results will be disseminated to parents, ex-patients and members of the public through the Imperial College Neonatal Data Analysis Unit website, social media and strong links between the authors and parent/patient groups.


    During the 6-year study period, 129 883 infants received at least 1 day of intensive care in England; 4.9% (6,346) of these received iNO. Use of iNO increased over time from 3.4% (1293/37 885) in 2010–2011 to 6.4% (3112/48 838) in 2014–2015.

    When analysed by gestational age band over the entire study period, 9.9% (1959/19 727) of infants born <29 weeks received iNO; corresponding percentages are 2.8% (1152/41 133) for 29–33 weeks and 4.7% (3235/69 022) for ≥34 weeks (tables 1–3). Mortality among iNO-treated infants decreased over time in all gestational age groups.

    Table 1

    Patient demographics and outcomes for infants born less than 29 weeks gestation admitted to neonatal units in England and treated with iNO

    Table 2

    Patient demographics and outcomes for infants born 29–33 weeks’ admitted to neonatal units in England and treated with iNO

    Table 3

    Patient demographics and outcomes for infants born >34 weeks’ gestation admitted to neonatal units in England and treated with iNO

    By gestational age bands

    Less than 29 weeks

    31% (1959/6346) of infants who received iNO were born <29 weeks of gestation (table 1). Among infants born in the later epoch, a lower proportion had diagnoses of prolonged rupture of membranes or pulmonary hypoplasia recorded and a higher proportion had respiratory distress syndrome (RDS) recorded and received surfactant. (table 1). Of 282 had congenital heart disease; the most common were atrial or ventricular septal defects (67%) (online supplemental table 2).

    29–33 weeks

    Eighteen per cent (1152/6 346) of infants who received iNO were born at 29–33 weeks of gestation. A lower proportion of infants born in the later epoch had PPHN recorded and a higher proportion had RDS recorded, although surfactant use was lower in the later epoch. In the 2014–2015 epoch, iNO was initiated later and administered for a shorter duration (table 2). Of 264 infants had congenital heart disease; 52% were atrial or ventricular septal defects (online supplemental table 2).

    Greater than or equal to 34 weeks

    Fifty-one per cent (3235/6346) of infants who received iNO had a gestational age of ≥34 weeks at birth. The proportion of these infants who received iNO increased marginally between 2010–2011 and 2014–2015. A lower proportion of these infants born in the later epoch had prolonged rupture of membranes, PPHN or meconium aspiration syndrome; and a higher proportion had RDS recorded and received surfactant. iNO was initiated later and administered for a shorter duration (table 3). Of 616 of these infants who received iNO had congenital heart disease and 41.6% (256/616) were atrial or ventricular septal defects (online supplemental table 2).

    Comparison between tertiary units

    There was wide variation in the proportion of infants receiving intensive care who also received iNO between the 47 tertiary neonatal intensive care units in England across all gestation groups (figure 1A). This was especially marked among infants <29 weeks of gestation where iNO use varied between 0.7% and 36.5% (figure 1B).

    Figure 1

    (A) iNO use for tertiary neonatal units for all gestational ages. (B) iNO use for tertiary neonatal units for infants born <29 weeks. (C) iNO use for tertiary neonatal units for infants born 29–33 weeks. (D) iNO use for tertiary units for infants born ≥34 weekshe numbers of infants receiving intensive care for more than one day in 2014–2015 (denominator) are not presented.

    When considering unit-level trends over time, iNO use in >29 week gestation infants increased between 2010–2011 and 2014–2015 in almost all units (figure 1C); however, a more mixed picture was seen in less preterm infants (figure 1D).


    In this large population-level study, we found that almost 1 in 20 infants who received any period of intensive care at an English neonatal unit were treated with iNO, that this rate almost doubled between 2010–2011 and 2014–2015 and that the temporal increase in iNO use was seen across all gestational ages. The temporal increase was most evident among more preterm infants <34 weeks, in whom the use of iNO increased threefold from 2.4% to 8.2% and where evidence for iNO is most lacking. There was a similar 3–4-fold increase in rates of iNO use for infants born <29 weeks and 29–33 weeks, from 4.9% to 15.9% and from 1.1% to 4.8% for infants, respectively. In the most preterm group, an additional 690 infants born <29 gestational weeks were treated with iNO in 2014–2015 compared with 2010–2011.

    It is difficult to compare these data with internationally reported iNO usage rates because other studies commonly report rates as a proportion of all neonatal admissions, whereas we report rates as a proportion of infants receiving neonatal intensive care. We used this denominator because of differences in the organisation of neonatal care (use of a networked model of care in the UK results in numerous transfers between neonatal units as part of routine care) and to minimise the impact of variations in practice around admissions of term infants for short periods. Rates of iNO usage in US studies are reported between 0.9% and 1.3%2 3 of all neonatal admissions. To our knowledge, this is one of the largest studies of iNO use in neonatal practice; other studies have reported iNO use in various US healthcare organisations (including children’s hospitals) and in all admissions including infants receiving lower acuity categories of neonatal care.1 4 9 10

    The Canadian Neonatal Network (CNN) found similar rates (1 in 25; 4.2%) of iNO use among infants born <34 weeks between 2010 and 2013. As different gestational age categories were used, direct comparisons cannot be made, but the use of iNO was broadly similar to the recent UK figures; however, in contrast to the increasing use in the UK, iNO use was stable across the 4 years in the CNN.11

    Approximately half of all infants who received iNO in this study were born at <34 weeks of gestation. This is relevant because the licenced indication for iNO limits treatment to newborn infants ≥34 weeks of gestation with hypoxic respiratory failure associated with clinical or echocardiographic evidence of pulmonary hypertension.12 This finding is, however, broadly consistent with other studies from the US and Europe, which showed that 40%–46% of all treated infants were <34 weeks of gestation.3 13 Treatment rates for preterm infants in this study (5.1% of preterm infants <34 weeks of gestation) were comparable to other studies from the US reporting rates of 2.6% to 7.2% in the same gestation groups,1 4 9 10 and in this comparison, the different denominator in US studies is less likely to influence results as the majority of more preterm infants will receive intensive care.

    We find that not only is off-label treatment with iNO of preterm infants <34 weeks of gestation widespread but also is increasing—particularly in the most preterm infants. The evidence base supporting routine use in these most preterm infants, both in respect of safety and efficacy, is weakest.2–4 Post hoc analyses from a study which randomised 420 neonates born <34 weeks of gestation to placebo or iNO found an apparent increase in mortality and higher rate of intraventricular haemorrhage in infants with a birth weight ≤1000 g.14

    The reason for increasing use of iNO off-label in particularly in the most preterm infants is not known but is likely to be multifaceted and reflect the absence of other proven ‘rescue’ cardiorespiratory interventions for these smaller infants with severe hypoxaemic respiratory failure (such as extracorporeal membrane oxygenation) and full reimbursement of off-label iNO use in England. Furthermore, there is some limited evidence for the use of iNO in specific groups of preterm infants including those born following preterm prolonged rupture of membranes and those with echocardiographic criteria of PPHN physiology, supported by expert opinion and consensus statements.15–18 There is growing experience in the use of iNO and the immediate short-term oxygenation response can be gratifying for clinicians and may encourage further use. However, whether the short-term benefit in oxygenation is translated into longer term benefit in preterm infants is unknown and needs further investigation. Moreover, the perception of absence of harm should not be extrapolated from term infants simply because there is a lack of convincing evidence of harm in preterm infants.

    Treatment with iNO was started later and duration of treatment was shorter in later epochs, suggesting that preterm infants were more commonly treated outside the acute respiratory phase. Although there is little evidence of efficacy of iNO as rescue therapy in acute respiratory failure or later ventilator-dependent chronic lung disease,19 20 we speculate that clinicians might be increasingly willing to use off-label iNO in such circumstances.

    This study also demonstrates large variation between English neonatal units in rates of iNO use, in keeping with that reported in recent US studies1 10 where a similar degree of variation from 0.4% to 21.9% was seen in iNO use in preterm infants between 13 National Institute of Child Health and Human Development (NICHD) neonatal research network centres. The variation between neonatal units in the US decreased following publication of national guidance.21 Such national guidance is not available for the UK but might help standardise practice in this area if it was to be developed.

    Overall mortality decreased in iNO-treated infants during the study period. This trend mirrors national data reporting improved survival in extremely preterm infants in England22 over a similar timeframe. The lower mortality seen in later epochs may also reflect a change in case mix as iNO therapy is offered more readily to infants with less severe cardiorespiratory failure. This type of ‘therapeutic creep’ has been described with other neonatal interventions.23 This study was not designed to analyse changes in outcomes beyond simple descriptive data.

    The strengths of this study include the use of a large national data set derived from electronic patient data routinely entered by health professionals at the point of care, which has been shown to be accurate and complete. This contrasts with previous similar reports such as those from the National Institute of Child Health and Development Neonatal Research Network and the Pediatrix Medical Group that have focused on admissions to tertiary neonatal units or to a large network of neonatal care providers, respectively.3 9 Limitations of this study include that data held in the NNRD are recorded as part of routine clinical care and we cannot exclude the possibility of incomplete or inaccurate data. Also, we did not set out to capture information about neonatal iNO use in other critical care settings, such as paediatric or cardiac intensive care units, and these data would have been excluded from this study. Our study was also not designed to describe specific aspects of iNO therapy such as indication for use and dosage regimens.

    Our study describes the increasing use of iNO, especially in more preterm infants, but was not designed to address the issue of potential benefits and risks of this practice. While iNO might be effective in certain subgroups of preterm infants such as those with pulmonary hypoplasia and/or PPHN physiology, its short-term and long-term safety has not yet been established. Potential concerns include an association between neonatal iNO therapy and pulmonary toxicity, brain injury and an increased risk of childhood cancer.24 25 iNO is also one of the most expensive treatments available in neonatal care and there are likely to be resource implications of increasing use. Although there are limited data on costs of iNO therapy in the UK,26 estimates from the USA suggest a cost of approximately US$125/hour or US$3000/day.27

    In summary, the use of iNO in English neonatal units has almost doubled between 2010 and 2015, with the most notable increase seen in the most premature infants. There was substantial variation in iNO use between units. Approximately half of the treated infants were preterm <34 weeks of gestation in whom iNO was used off-label and without high-quality evidence of efficacy or safety. Given the cost of iNO therapy, limited evidence of efficacy in preterm infants, and potential for harm, we suggest that exposure to iNO should be limited, ideally to infants included in research studies (either observational or RCT) or within a protocolised pathway that permits a short trial of iNO to assess acute oxygenation response. Development of consensus guidelines might also help standardise practice.


    We thank the families that agreed to the inclusion of their infants’ data in the NNRD, the health professionals in the UK Neonatal Collaborative who recorded the data.


    Supplementary materials

    • Supplementary Data

      This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.


    • Twitter @DrCGale, @DrCBattersby

    • Collaborators We wish to acknowledge all neonatal in the UK Neonatal collaborative who contribute data to the NNRD. Matthew Babirecki (Airedale General Hospital); Anand Kamalanathan (Arrowe Park Hospital); Tim Wickham (Barnet Hospital); Kavi Aucharaz (Barnsley District General Hospital); Aashish Gupta (Basildon Hospital); Nicola Paul (Basingstoke & North Hampshire Hospital); L M Wong (Bassetlaw District General Hospital); Anita Mittal (Bedford Hospital); Lindsay Halpern (Birmingham City Hospital); Pinki Surana (Birmingham Heartlands Hospital); Matt Nash (Birmingham Women's Hospital); Sunita Seal (Bradford Royal Infirmary); Ahmed Hassan (Broomfield Hospital, Chelmsford); Karin Schwarz (Calderdale Royal Hospital); Shu-Ling Chuang (Chelsea & Westminster Hospital); Aiwyne Foo (Chesterfield & North Derbyshire Royal Hospital); Jo Anderson (Colchester General Hospital); Graham Whincup (Conquest Hospital); Stephen Brearey (Countess of Chester Hospital); John Chang (Croydon University Hospital); Yee Aung (Cumberland Infirmary); Abdul Hasib (Darent Valley Hospital); Mehdi Garbash (Darlington Memorial Hospital); Alex Allwood (Derriford Hospital); Pauline Adiotomre (Diana Princess of Wales Hospital); Nigel Brooke (Doncaster Royal Infirmary); Abby Deketelaere (Dorset County Hospital); K Abdul Khader (East Surrey Hospital); Ruth Shephard (Epsom General Hospital); Sanghavi Rekha (Frimley Park Hospital); Anas Olabi (Furness General Hospital); Mukta Jain (George Eliot Hospital); Jennifer Holman (Gloucester Royal Hospital); Pinki Surana (Good Hope Hospital); Stanley Zengeya (Great Western Hospital); Geraint Lee (Guy's & St Thomas' Hospital); Sobia Balal (Harrogate District Hospital); Cath Seagrave (Hereford County Hospital); Tristan Bate (Hillingdon Hospital); Hilary Dixon (Hinchingbrooke Hospital); Narendra Aladangady (Homerton Hospital); Hassan Gaili (Hull Royal infirmary); Matthew James (Ipswich Hospital); M Lal (James Cook University Hospital); Ambadkar (James Paget Hospital); Poornima Pandey (Kettering General Hospital); Ravindra Bhat (Kings College Hospital); Simon Rhodes (King's Mill Hospital); Vinay Pai (Kingston Hospital); Savi Sivashankar (Lancashire Women and Newborn Centre); Lawrence Miall (Leeds Neonatal Service); Jonathan Cusack (Leicester General Hospital); Venkatesh Kairamkonda (Leicester Royal Infirmary); Michael Grosdenier (Leighton Hospital); Ajay Reddy (Lincoln County Hospital); J Kefas (Lister Hospital); Christopher Dewhurst (Liverpool Women's Hospital); Jennifer Birch (Luton & Dunstable Hospital); Gail Whitehead (Macclesfield District General Hospital); Krishnamurthy (Manor Hospital); Ghada Ramadan (Medway Maritime Hospital); I Misra (Milton Keynes General Hospital); Chris Knight (Musgrove Park Hospital); Rob Negrine (New Cross Hospital); Imdad Ali (Newham General Hospital); Prakash Thiagarajan (Nobles Hospital); Mark Dyke (Norfolk & Norwich University Hospital); Michael Selter (North Devon District Hospital); P Kamath (North Manchester General Hospital); Neeraj Jain (North Middlesex University Hospital); Subodh Gupta (Northampton General Hospital); Laura Winder (Northumbria Specialist Emergency Care Hospital); Richard Nicholl (Northwick Park Hospital); Steven Wardle (Nottingham City Hospital); Steven Wardle (Nottingham University Hospital (QMC)); Andreea Bontea (Ormskirk District General Hospital); Eleri Adams (Oxford University Hospitals, John Radcliffe Hospital); Katharine McDevitt (Peterborough City Hospital); Ajay Reddy (Pilgrim Hospital); David Gibson (Pinderfields General Hospital); Minesh Khashu (Poole General Hospital); Chinnappa Reddy (Princess Alexandra Hospital); Mark Johnson (Princess Anne Hospital); P Amess (Princess Royal Hospital); Deshpande (Princess Royal Hospital); Elizabeth Sleight (Princess Royal University Hospital); Charlotte Groves (Queen Alexandra Hospital); Lidia Tyszcuzk (Queen Charlotte's Hospital); Anne Dale (Queen Elizabeth Hospital, Gateshead); Glynis Rewitzky (Queen Elizabeth Hospital, King's Lynn); Olutoyin Banjoko (Queen Elizabeth Hospital, Woolwich); Bushra Abdul-Malik (Queen Elizabeth the Queen Mother Hospital); Dominic Muogbo (Queen's Hospital, Burton on Trent); Khalid Mannan (Queen's Hospital, Romford); Angela D'Amore (Rosie Maternity Hospital, Addenbrookes); Shameel Mattara (Rotherham District General Hospital); Christos Zipitis (Royal Albert Edward Infirmary); Peter De Halpert (Royal Berkshire Hospital); Paul Settle (Royal Bolton Hospital); Paul Munyard (Royal Cornwall Hospital); John McIntyre (Royal Derby Hospital); Chrissie Oliver (Royal Devon & Exeter Hospital); Lucinda Winckworth (Royal Hampshire County Hospital); Joanne Fedee (Royal Lancaster Infirmary); Natasha Maddock (Royal Oldham Hospital); Richa Gupta (Royal Preston Hospital); Jyoti Kapur (Royal Stoke University Hospital); Ben Obi (Royal Surrey County Hospital); P Amess (Royal Sussex County Hospital); Stephen Jones (Royal United Hospital); Naveen Athiraman (Royal Victoria Infirmary); Chandan Gupta (Russells Hall Hospital); Jim Baird (Salisbury District Hospital); Kirsten Mack (Scarborough General Hospital); Pauline Adiotomre (Scunthorpe General Hospital); Vineet Gupta (Southend Hospital); Faith Emery (Southmead Hospital); Charlotte Huddy (St George's Hospital); Ralf Hartung (St Helier Hospital); Akinsola Ogundiya (St Mary's Hospital, Isle of Wight); Lidia Tyszcuzk (St Mary's Hospital, London); Ngozi Edi-Osagie (St Mary's Hospital, Manchester); Pamela Cairns (St Michael's Hospital); Peter Martin (St Peter's Hospital); Nick Brennan (St Richard's Hospital); Carrie Heal (Stepping Hill Hospital); Sanjay Salgia (Stoke Mandeville Hospital); Majd Abu-Harb (Sunderland Royal Hospital); Jacqeline Birch (Tameside General Hospital); Porus Bastani (The Jessop Wing, Sheffield); Marice Theron (The Royal Free Hospital); Vadivelam Murthy (The Royal London Hospital); Siba Paul (Torbay Hospital); Hamudi Kisat (Tunbridge Wells Hospital); Giles Kendall (University College Hospital); Puneet Nath (University Hospital Coventry); Ozioma Obi (University Hospital Lewisham); Mehdi Garbash (University Hospital of North Durham); Hari Kumar (University Hospital of North Tees); Chris Rawlingson (Victoria Hospital, Blackpool); Delyth Webb (Warrington Hospital); Bird (Warwick Hospital); Sankara Narayanan (Watford General Hospital); Yee Mon Aung (West Cumberland Hospital); Eleanor Hulse (West Middlesex University Hospital); Ian Evans (West Suffolk Hospital); Rekha Sanghavi (Wexham Park Hospital); Caroline Sullivan (Whipps Cross University Hospital); Ros Garr (Whiston Hospital); Wynne Leith (Whittington Hospital); Vimal Vasu (William Harvey Hospital); Liza Harry (Worcestershire Royal Hospital); Katia Vamvakiti (Worthing Hospital); Ngozi Edi-Osagie (Wythenshawe Hospital); Megan Eaton (Yeovil District Hospital); Sundeep Sandhu (York District Hospital)

    • Contributors Study concept and design: NVS, CG. Development of source code: KO, SJ, CB. Analysis and interpretation of data: NVS, SJ, CG, CB. Writing and revision of the manuscript: NVS, SJ, KO, CG, CB.

    • Funding Data extraction was funded through discretionary funding from the University of Liverpool held by NS.

    • Competing interests CG reports grants from Medical Research Council, the National Institute for Health Research, the Mason Medical Research Foundation, Rosetrees Foundation and Canadian Institute for Health Research outside the submitted work; and grants and personal fees to attend an educational conference from Chiesi Pharmaceuticals outside the submitted work; he is a voluntary, unremunerated member of the Neonatal Data Analysis Unit Steering Board, which oversees the National Neonatal Research Database (NNRD), and is vice-chair of the NIHR Research for Patient Benefit London Regional Assessment Panel. CB reports grants from the National Institute for Health Research outside the submitted work; and grants and personal fees to attend educational conferences from Chiesi and Abbvie Pharmaceuticals outside the submitted work; and is a member of the NIHR HTA prioritisation committee.

    • Patient consent for publication Not required.

    • Ethics approval This study using anonymised data was approved by the West of Scotland Research Ethics Committee 5; reference number 16/WS/0228.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data availability statement Data are available upon reasonable request. All data relevant to the study are included in the article or uploaded as supplementary information. The NNRD is not immediately available to the public. However, requests can be made by researchers to acquire access through

    • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.