Groups
We divided the patients in two groups according to their response to diuretics in terms of decreasing respiratory support (RS). We registered RS at the time of each LU, and we categorized it as: invasive mechanical ventilation (IMV), nasal intermittent positive pressure ventilation (NIV), nasal continuous positive airway pressure (nCPAP), high flow nasal cannula (HFNC) and none. As the diuretics’ effect in pulmonary function tests have been described to occur as late as four weeks afterwards 21, we compared the highest RS two weeks before LU, with the lowest RS four weeks after LU.
- Responders: the lowest RS four weeks after diuretics is, at least, one level lower than the higher RS two weeks before diuretics. - Non-responders: the lowest RS four weeks after diuretics is the same or worse than the highest RS two weeks before diuretics.
As the time at which infants required diuretics was different, we centered the date of LU in the day when diuretics were started. We created these groups of dates: ”32 days or more before diuretics” (B1), ”31-24 days before diuretics” (B2), ”23-16 days before diuretics” (B3), ” 15-8 days before diuretics” (B4), ”7-4 days before diuretics” (B5), ”3 days before to 1 day after diuretics” (T0), ”2 to 5 days after diuretics” (A1), ”6 to 9 days after diuretics” (A2), ”10 to 17 days after diuretics” (A3), ”18 to 25 days after diuretics” (A4), ”26 to 33 days after diuretics” (A5), ”34 or more days after diuretics” (A6).
BPD was defined according to Walsh et al. definition24: mild BPD (oxygen requirement for the first 28 days but in room air at 36 weeks’ PMA), moderate BPD (oxygen requirement for the first 28 days and oxygen <30% at 36 weeks’ PMA. A room-air challenge was performed in these infants and only those that failed the reduction (oxygen saturation 80-87% for 5 minutes, or <80% for 1 minute) were diagnosed as moderate BPD), and severe BPD (oxygen requirement for the first 28 days and oxygen >30% or continuous positive airway pressure or mechanical ventilation at 36 weeks’ PMA).