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Neurodevelopmental outcomes of extremely low birthweight infants randomised to different PCO2 targets: the PHELBI follow-up study
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  • Published on:
    Response to letter re: ‘Combinations of subgroup analyses and impact on results’
    • Ulrich H. Thome, Prof. Dr. med. Division of Neonatology, Department of Women's and Children's Medicine, University Hospital of Leipzig

    We thank the letter authors for commending most of our protocol decisions. A multicenter trial is always associated with a number of compromises, e.g.  between standardization and freedom of therapy, between insufficient and overzealous data collection, and between too few and too many exploratory statistical tests.


    For detecting BPD, we used criteria that included all cases with requirement of supplemental oxygen or mechanical support at a postmenstrual age of 36 weeks. This definition was the same as moderate or severe BPD in the more recently formulated consensus definition, and has been used in many other previous trials, testing ventilation modes, high-frequency ventilation, steroid use, permissive hypercapnia, and many others. This made our results comparable to previously published data.

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    Conflict of Interest:
    None declared.
  • Published on:
    Combinations of subgroup analyses and impact on results
    • Eden A Andrew, Medical practitioner Mercy Hospital for Women
    • Other Contributors:
      • James Holberton, Neonatologist
      • Gillian Opie, Neonatologist
      • Andrew Watkins, Neonatologist

    We read with interest the follow up study by Thome and colleagues assessing neurodevelopmental outcomes of the extremely low birth weight (ELBW) infants from the Permissive Hypercapnia in Extremely Low Birthweight Infants (PHELBI) trial1.

    This study makes an important contribution to the evidence-base on the strategy of permissive hypercapnia for ELBW infants. It is a well-powered, multicentre trial and we commend the authors for the ambitious decision to include only intubated ELBW infants and also the use of a clinician-guided treatment protocol. While the methodology allows some systematic bias, there is strong external validity with a patient population representative of ‘real-life’ clinical practice.

    We question the choice to combine the subgroups with moderate and severe bronchopulmonary dysplasia (BPD) for statistical analysis. In Table 2, we note the non-significant p-value for the combined outcome of moderate/severe BPD of 0.30 and no reported p-values for the individual subgroups moderate BPD and severe BPD. Using the raw data provided in Table 2, we calculate a p-value for severe BPD as significant at 0.01, suggesting an increase.

    There is considerable clinical difference between patients with moderate BPD (requiring FiO2 <30% at 36 weeks or discharge) and those with severe BPD (requiring FiO2 ≥30% and/or positive pressure ventilation)2. Other than increased risk of mortality and respiratory disease, severity of BPD correlates with incr...

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    Conflict of Interest:
    None declared.