Article Text

Towards a harmonized bronchopulmonary dysplasia definition: a study protocol for an international Delphi procedure
  1. Trixie A Katz1,2,
  2. Eduardo Bancalari3,
  3. Sanne J Gordijn4,
  4. Rosemary D Higgins5,
  5. Tetsuya Isayama6,
  6. Erik A Jensen7,
  7. Martin Offringa8,
  8. J Jane Pillow9,
  9. Prakesh S Shah10,
  10. Roger F Soll11,
  11. Benjamin Stoecklin12,
  12. Suzanne M Mugie1,2,
  13. Anton H van Kaam1,2,
  14. Wes Onland1,2
  1. 1Amsterdam Reproduction & Development, Amsterdam, The Netherlands
  2. 2Department of Neonatology, Emma Childrens' Hospital UMC, Amsterdam, The Netherlands
  3. 3Division of Neonatology, Jackson Memorial Hospital, Miami, Florida, USA
  4. 4Department of Obstetrics and Gynecology, UMCG, Groningen, The Netherlands
  5. 5Research and Sponsored Programs, Florida Gulf Coast University, Fort Myers, Florida, USA
  6. 6Division of Neonatology, National Center for Child Health and Development, Tokyo, Japan
  7. 7Division of Neonatology, The Children's Hospital, Philadelphia, Pennsylvania, USA
  8. 8Division of Neonatology, Hospital for Sick Children, Toronto, Ontario, Canada
  9. 9Division of Pediatrics, Medical School, The University of Western Australia and Telethon Kids Institute, Perth, Washington, Australia
  10. 10Division of Neonatology, Mount Sinai Hospital, Toronto, Ontario, Canada
  11. 11Division of Neonatology, University of Vermont Medical Center, Burlington, Vermont, USA
  12. 12Department of Neonatology, University Children's Hospital Basel, Basel, Switzerland
  1. Correspondence to Dr Wes Onland; w.onland{at}


Introduction Bronchopulmonary dysplasia (BPD) remains the most common complication of preterm birth with lifelong consequences. Multiple BPD definitions are currently used in daily practice. Uniformity in defining BPD is important for clinical care, research and benchmarking. The aim of this Delphi procedure is to determine what clinicians and researchers consider the key features for defining BPD. With the results of this study, we hope to advance the process of reaching consensus on the diagnosis of BPD.

Methods and analysis A Delphi procedure will be used to establish why, when and how clinicians propose BPD should be diagnosed. This semi-anonymous iterative technique ensures an objective approach towards gaining these insights. An international multidisciplinary panel of clinicians and researchers working with preterm infants and/or patients diagnosed with BPD will participate. Steering committee members will recruit potential participants in their own region or network following eligibility guidelines to complete a first round survey online. This round will collect demographic information and opinions on key features of BPD definitions. Subsequent rounds will provide participants with the results from the previous round, for final acceptance or rejection of key features. Statements will be rated using a 5-point Likert scale. After completing the Delphi procedure, an (online) consensus meeting will be organised to discuss the results.

Ethics and dissemination For this study, ethical approval a waiver has been provided. However, all participants will be asked to provide consent for the use of personal data. After the Delphi procedure is completed, it will be published in a peer-reviewed journal and disseminated at international conferences.

  • Neonatology
  • Qualitative research
  • Data Collection

Data availability statement

Data are available on reasonable request. Data are available on reasonable request, please contact corresponding author.

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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  • Bronchopulmonary dysplasia (BPD) remains the most common complication of preterm birth. The use of multiple heterogeneous BPD definitions results in unwanted variability in the reported frequency of BPD as an outcome for clinical care and research.


  • This Delphi procedure will identify key features (why, how and when) which, according to clinicians and researchers, are considered essential for a harmonized BPD definition. With our global coverage, we will be able to take national and regional differences in clinical practices and healthcare resource utilisation into account.


  • The results of this Delphi procedure will guide clinicians and researchers in reaching global consensus in defining BPD.


Bronchopulmonary dysplasia (BPD) is one of the most common complications of preterm birth. BPD is associated with short-term in-hospital morbidity and long-term adverse respiratory, cardiovascular and neurodevelopmental outcomes.1 2 Accurate criteria to establish the diagnosis and severity of BPD are important in translational and clinical research, but also in daily clinical care to decide on the use of therapies for prevention and treatment and to inform parents of the possible problems their child may experience in the future.3 The internationally accepted 1988-Shennan- and the 2001 National Institute Health (NIH)- BPD definition are the most used BPD definitions over the last two decades, but have been recently challenged by the emergence of other BPD definitions.4 Several reasons underpin the development of these new BPD definitions. First, neonatal care has improved significantly resulting in more premature survivors being exposed to lung injurious conditions and interventions at a much younger stage of lung development. These developments may have changed the disease entity and thus the accuracy of diagnosing BPD and predicting long-term outcomes.5 Second, high flow nasal cannula (HFNC) was implemented in daily clinical care in recent years: HFNC is a mode of respiratory support that was not incorporated in the 2001-NIH definition as it was not in widespread use when the 2001-NIH definition was created. Therefore, it is unclear how infants treated with HFNC should be classified in terms of BPD severity in the 2001-NIH definition.

The newer BPD definitions use different parameters, timing of assessment and/or methods to diagnose BPD and its severity compared with the 2001-NIH definition.6–10 First, they do not incorporate the cumulative days of oxygen as a criterion and have different thresholds of respiratory support and supplemental oxygen for BPD severity classification at 36 weeks postmenstrual age (PMA).8 9 Second, in contrast to the adapted 2001 NIH definition,11 no oxygen reduction testing is required. Furthermore, one new definition suggests postponing the timing of the BPD diagnosis up to 40 weeks PMA.7 Finally, some authors suggest to move away from a diagnosis based on clinical treatment altogether, and use pathophysiological parameters to define BPD.10

Hines et al demonstrated that these various definitions for BPD are used frequently in the literature.4 More importantly, researchers and clinicians should realise that studies show that the incidence of BPD varies with the use of any particular BPD definition, which emphasises the need for a harmonized definition.4 12 This ‘definition-driven’ heterogeneity in BPD incidences, especially in the grades of severity, leads to discrepancies in clinical and research outcomes between studies. Further, it impairs comparisons of BPD between centres and the interpretation of the results of randomised controlled trials investigating BPD as an outcome.12–14 Uniformity in the definition for BPD is an essential part of reliable data comparison and data synthesis for clinical purposes, benchmarking, quality improvement as well as developing new therapeutic strategies for BPD.4

In summary, there is a need for a consensus approach to the diagnosis of BPD. To develop such a definition based on objective data, a Delphi procedure can be used to help reach consensus on the primary reason (why) to establish the BPD diagnosis, to assess the optimal timing of the diagnosis (when), and to assess the (minimal) parameters and/or procedures needed to establish high accuracy (how), including the feasibility and effort of collecting those parameters. In preparation for an international consensus meeting, a Delphi procedure beginning with an online questionnaire is a widely used and effective method to gain insight and opinions on a specific topic from a multidisciplinary group of experts.15–17

The aim of this Delphi procedure is to guide clinicians and researchers in reaching global consensus in defining BPD by acquiring information on which features of BPD definition are important.

Methods and analysis

Steering committee

A study team from the Amsterdam University Medical Centers (Amsterdam UMC) was formed to undertake this Delphi procedure. Next, an impartial expert on Delphi procedures working in a different field of medicine was invited to join the steering committee to moderate the procedure, with the goal of minimising bias and maintaining objectivity. After, BPD (definition) experts were identified through a literature search and invited to join the steering committee. These BPD experts were consulted on the design of the Delphi procedure and the questionnaires, and were asked to disseminate the survey invitation to potential participants in their own region or network. The steering committee reached agreement on participant selection, consensus thresholds and survey format.17

Selection and identification of participants

Participants will be asked to complete the Delphi survey. To ensure sufficient diversity, we will include clinically oriented and/or research-oriented healthcare professionals with relevant backgrounds, for example; neonatologists, paediatricians (eg, providing outpatient clinical care of preterm infants), pulmonologists and ventilation practitioners or respiratory therapists. Administrators and regulators involved in neonatal care will also be invited to participate. We aim to achieve global coverage, by including participants from all continents. Participants will be recruited from all different levels of care (regional centres to specialised BPD referral centres). To prevent selection bias, initial survey invitations will be forwarded to national network list servers and no individual emails will be sent out. Lay experts and patients (representatives) will not be included as participants. The aim of this Delphi procedure is not to establish a core outcome dataset or other items that would benefit from patient or parental input.


Participants will be identified by the study team and the steering committee members (figure 1). The steering committee members will be asked to disseminate an open-link invitation to the survey to participants in their region and/or network while adhering to the guidelines for eligibility (box 1).

Box 1

Eligibility criteria for participants

Participant can be categorised in at least one of the following groups of healthcare professionals:

  1. (Fellow/attending) neonatologist providing clinical care to preterm infants (including all levels of care).

  2. Respiratory therapist or ventilation practitioner providing clinical care to preterm infants.

  3. Nurse practitioner or physician assistant providing clinical care to preterm infants.

  4. Researcher with publications on developing or established BPD in preterm.

  5. General paediatrician/other specialist who provides clinical/outpatient care for infants with BPD.

  6. Administrator or regulator in neonatal care (eg, at the FDA/EMA)

  • BPD, bronchopulmonary dysplasia; FDA, Federal Drug Association; EMA, European Medicines Agency.

Figure 1

Participants’ recruitment process.

An email reminder to the steering committee will be sent 2 and 3 weeks after disseminating the primary invitation. In subsequent rounds, a group reminder will be sent after 2 weeks, and non-responders will receive a final reminder after 4 weeks. Participants who do not complete one of the subsequent rounds will be excluded from the study and the analyses.

Sample size and composition

Sample sizes in Delphi procedures are variable, ranging from 10 to over 1000 participants, with no agreement in the literature on the ideal size.18 No lower or upper limit will be set as larger panels increase the reliability of the outcomes.18


One of the key features of a Delphi technique is that the procedure is anonymous on group level, also known as semianonymity. However, the participant is not anonymous to the researcher. At the conclusion of the process, participants who have completed each round will be offered the choice to remain anonymous or receive acknowledgement in the publication.

Design and content of the survey

All electronic surveys will be developed in the electronic data capture (EDC) system Castor EDC 2019; online available at: Each round of the survey will be accompanied by a cover sheet containing background information and aims. After the first round, the subsequent rounds will include results from the previous rounds. The participants will be asked to state the extent to which they agree on the different statements regarding features of the BPD definitions using a 5-point Likert scale (1: strongly disagree; 2: disagree; 3: neutral; 4: agree; 5: strongly agree). A 5-point Likert scale is commonly used in Delphi procedures. We chose this 5-point scale after careful consideration as studies show an increased response rate and quality along with reducing respondents’ dissatisfaction with a 5-point compared with a 3-point or 7-point scale.18 20

Survey development

Statements/questions for the first-round survey will be developed with the study team’s expertise and partly based on key features from current BPD definitions (eg, timing of diagnosis). The survey of the first round will be thoroughly revised by the steering committee members and discussed in an (online) meeting. Communication experts will be consulted on their expertise of interpretation and formulation of the questions and statements. The survey will also be tested by a research data manager to identify any technical or data management issues. Finally, a small pilot study will be performed inviting a group of neonatologists to fill in the survey. The survey will be adjusted based on their feedback before being finalized (see online supplemental material for the final first round survey).

Supplemental material


A minimum of two rounds will be undertaken to allow the participants to complete the Delphi process (figure 2). It is anticipated that between two and four rounds will be necessary to achieve consensus.

Figure 2

Delphi rounds process and consensus criteria for adopting statements.

First round

The first-round questionnaire will consist of 20–30 questions, and it will take approximately 10–15 min to complete. First, demographic characteristics of the participants will be collected including region of practice, main field of practice, current position, years of experience in (neonatal) care, level of neonatal care at the current institute, amount of time spent on research and clinical work. Second, data on their current use of BPD definitions will be collected. Next, participants will be asked to respond to a series of statements on key features of a BPD definition using a 5-point Likert scale. Finally, the participants will be asked to suggest additional parameters for a BPD definition or other remarks regarding the survey itself in an open field box. These suggestions will be discussed by the study team for incorporation into subsequent rounds.

Subsequent rounds

Once again, participants will be asked to state the extent to which they agree with the newly suggested statements using a 5-point Likert scale. Statements with a median score ≥4 will be presented for final acceptance, and statements with a median score <4 will be presented for final rejection (figure 2). Parameters that do not reach consensus in the second round will be presented in subsequent rounds using a Best-Worst scale21 (figure 2).

Definition of consensus

Multiple cut-offs for consensus are reported in the literature.17 22 A minimum of 70% agreement is most frequently reported and will be used to define consensus in this Delphi procedure. If too many parameters reach acceptance/consensus during the procedure, the cut-off will be increased to 80% to achieve our objectives.

Statistical analysis

The quantitative data will be entered into SPSS (IBM Corp. Released 2021. IBM SPSS Statistics for Windows, Version 28.0., IBM) for analysis and descriptive statistics, such as medians and IQRs, will be reported for each statement to be fed back to the participants in subsequent rounds.

Data collection

After all participants have provided informed consent, only limited identifying information (name and email) will be registered. This identifiable information will be stored separately from the answers to the questionnaire and will only be used for the purpose of direct feedback, reminder emails, and if applicable, for acknowledgement of contribution.

Study status and dissemination

The steering committee members were identified and invited in the third quarter (Q3) of 2022, and all agreed to participate. The Delphi protocol was written and discussed in online meetings between Q3 of 2022 and Q1 of 2023. The development of the Delphi questionnaire started in Q3 of 2022 and the pilot study finalised in Q1 of 2023. The anticipated start of the online Delphi study is May 2023. We will finalise the procedure in Q4 2023, analyse the data in Q1 in 2024, and anticipate hosting an (online) meeting during an international conference in Q2 of 2024 to optimise the uptake of the results from this Delphi procedure. Dissemination of the results will be accomplished by publication in an international peer-reviewed journal and by presentations at (international) conferences.


Currently, clinicians and researchers around the world use different definitions of BPD. The heterogeneity in how BPD is defined makes comparison of the BPD incidence between different neonatal intensive care units, data collection in large databases and interpretation of study results difficult, if not impossible. To address this problem, neonatal caregivers and researchers should all use a harmonised BPD definition.

This Delphi procedure is the first step towards a harmonised BPD definition. It will provide insight in key features that, based on the opinion of clinicians and experts in BPD, should be used as criteria in a future, harmonised definition of BPD. In doing so, we will take differences between countries in clinical practices and resources use into account.

To ensure that the results of this Delphi procedure will find their way into a future practice, an online/in person meeting will be organised to discuss the results of the Delphi procedure. These results will provide a first step in guiding clinicians and researchers in reaching global consensus in defining BPD. Future steps may include coming to a consensus on which currently available BPD definition should be validated and implemented in current practice or a data-driven approach in designing a new BPD definition.

Data availability statement

Data are available on reasonable request. Data are available on reasonable request, please contact corresponding author.

Ethics statements

Patient consent for publication

Ethics approval

This Delphi procedure seeks opinions and information from medical professionals and does not include patients. The medical research ethics committee of the Amsterdam University Medical Centers (Amsterdam UMC) was contacted and confirmed that the Dutch Medical Research Involving Human Subject Act does not apply to this study and that Institutional Review Board (IRB) review is not necessary. However, electronic informed consent will be obtained from all healthcare professionals/participants for the use of personal data. All data will be handled in accordance with privacy laws.


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.


  • Contributors TAK: conceptualisation/design, methodology, writing-drafting the initial manuscript. EB: methodology, writing-review or editing of the manuscript. SJG: methodology, writing-review or editing of the manuscript. RDH: methodology, writing-review or editing of the manuscript. TI: methodology, writing-review or editing of the manuscript. EAJ: methodology, writing-review or editing of the manuscript. MO: methodology, writing-review or editing of the manuscript. JP: methodology, writing-review or editing of the manuscript. PSS: methodology, writing-review or editing of the manuscript. RFS: methodology, writing-review or editing of the manuscript. BS: methodology, writing-review or editing of the manuscript. SMM: conceptualisation/design, methodology, writing-review or editing of the manuscript. AHvK: conceptualisation/design, methodology, supervision/oversight, writing-review or editing of the manuscript. WO: conceptualisation/design, methodology, supervision/oversight, writing-review or editing of the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were involved in the design, or conduct, or reporting, or dissemination plans of this research. Refer to the Methods section for further details.

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

  • 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.