Introduction

Early identification of preterm born infants most at risk for respiratory problems is challenging due to a lack of valid and feasible lung function tests. We aim to assess the value of the hypoxic challenge test (HCT) as a test for lung and pulmonary vascular function in preterm born infants with and without bronchopulmonary dysplasia (BPD).

Methods

Infants born <32 weeks of gestation were included. The HCT was performed at 6 months of age corrected for prematurity. A cut-off point of 85% oxygen saturation was used as test fail point. Echocardiographic parameters collected prior to and immediately after the HCT were used to evaluate pulmonary vascular reactivity: pulmonary artery acceleration time (PAAT)/right ventricle ejection time (RVET) ratio, eccentricity index, and systolic duration (SD) to diastolic duration (DD) time ratio. For each infant, the change in pulmonary vascular reactivity caused by the HCT was calculated. Outcomes on respiratory morbidity were collected until 12 months of age corrected for prematurity. Differences in outcomes were evaluated between infants that failed and passed the HCT.

Results

We included 40 infants (21 severe BPD, 19 mild/no BPD). Eleven infants failed the HCT, of whom 8 with severe BPD (38.1%) and 3 with mild/no BPD (15.8%). No significant differences were seen in PAAT/RVET ratio (p=0.711), eccentricity index (p=0.954), and the SD/DD ratio (p=0.091), between passing or failing the HCT. The risk of re-hospitalization for respiratory infections in the first year was higher in infants failing the HCT (OR=6.86, 95% CI [1.03?45.6]).

Conclusion

The HCT is a valuable lung function test in preterm infants, but does not pick up on changes in pulmonary vascular reactivity.