An article published at the end of 2015, (I only just got the full-text) compared 3 diagnostic criteria for defining BPD. The original 36 week threshold by Andy Shennan, the NIH workshop definition, and the ‘physiologic’ definition requiring a room-air challenge as developed by Michele Walsh and colleagues. They also looked at a modification of the Shennan definition, to consider babies discharged before 36 weeks on room air as no BPD; and a modification of the NIH workshop definition to eliminate the requirement for oxygen therapy for at least 28 days, which eliminated the category ‘mild BPD’.

They looked at 765 babies under 29 weeks who arrived at 36 weeks post-menstrual age. There isn’t much difference between the modified Shennan and modified NIH definitions, and they both classified about 55% of the babies as not having BPD. The physiologic definition classified 52% as not having BPD but there were 16% of babies who were unclassified (compared to just 2% for the other definitions), mostly because they didn’t have the room air- challenge performed at the right time.

The article abstract ends with the following

Contemporary changes in management of infants, such as use of high-flow nasal cannula, limit application of existing definitions and may result in misclassification. A contemporary definition of bronchopulmonary dysplasia that correlates with respiratory morbidity in childhood is needed.

I certainly agree with that. It is of little importance to families whether a child comes out of oxygen just before or just after 36 weeks. even though there is a significant correlation of this with early childhood morbidity, there is much uncertainty, Violette, my daughter for example did not have BPD by the Shennan definition, did have mild BPD by the NIH workshop definition, and didn’t have BPD by the ‘physiologic’ definition. She did however have a cough, mild retractions, persistent tachypnea for many months after discharge; she was kept away from all child contact for months, apart from her older brother who was taken out of daycare because of her respiratory status, and had steroids a couple of times in the first year because of stridor.

I think trials that try and impact respiratory illness in the preterm infant should not be based on analyzing the duration of oxygen therapy, but on some indicator(s) of the impact of pulmonary damage on the well-being of the child and their  family. I think an outcome which took into account the need for oxygen at home, re-admission for respiratory disease during the first year of life, need for daily respiratory medications, impacts on activity levels, as examples, would be much more meaningful as a target for reducing lung injury.

There may well be a statistical correlation between 36 week oxygen requirement and important lung disease after discharge, but it won’t be a perfect relationship, and if you reduce “BPD” by current definitions, but have no effect on things that affect families, then you probably haven’t done much good.