Ventilatory response and stability of oxygen saturation during a hypoxic challenge in very preterm infants

Background: Preterm infants have immature control of breathing and impaired pulmonary gas exchange. We hypothesized that infants with bronchopulmonary dysplasia (BPD) have a blunted ventilatory response and peripheral oxygen saturation (SpO₂) instability during a hypoxic challenge. Methods: We evaluated the response to hypoxia in 57 very preterm infants (38 no BPD, 10 mild BPD, 9 moderate-to-severe BPD) at 36 weeks' postmenstrual age. The fraction of inspired oxygen (F_IO₂) was reduced stepwise at 5-min intervals to achieve peripheral SpO₂ between 86% and 95%. The lowest permissible F_IO₂ and SpO₂ were 0.14% and 86%. We recorded SpO₂, F_IO₂, and the respiratory signal (respiratory inductive plethysmography). We calculated respiratory rate (RR), tidal volume (V_T), minute ventilation (V_E), and respiratory drive (ratio between V_T and inspiratory time, V_T/T_I). SpO₂ variability was expressed as the interquartile range (IQR). Results: F_IO₂ was reduced from a median (Q1, Q3) of 0.21 (0.21, 0.21) to 0.17 (0.17, 0.18). We observed a marked individual variability in the ventilatory response to the hypoxic challenge, regardless of BPD severity. At the lowest permissible F_IO₂, 37 (65%) infants reduced their V_E, and 20 (35%) increased minute ventilation; 20 infants (35%) developed periodic breathing associated with increased SpO₂ IQR and lower SpO₂ minima, and 16 (28%) exhibited an oscillatory pattern in V_E and SpO₂ without end-expiratory pauses, regardless of BPD severity. Conclusion: In very preterm infants, a mild hypoxic challenge reduced ventilation, increased SpO₂ variability and periodic breathing regardless of BPD severity.