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 hypothesised 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 (FI O2 ) was reduced stepwise at 5-min intervals to achieve peripheral SpO2 between 86-95%. The lowest permissible FI O2 and SpO2 were 0.14 and 86%. We recorded SpO2 , FI O2 , and the respiratory signal (respiratory inductive plethysmography). We calculated respiratory rate (RR), tidal volume (VT ), minute ventilation (VE ), and respiratory drive (ratio between VT and inspiratory time, VT /TI ). SpO2 variability was expressed as interquartile range (IQR). Results: FI O2 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 FI O2 , thirty-seven (65 %) infants reduced their VE , and 20 (35 %) increased minute ventilation; twenty infants (35 %) developed periodic breathing associated with increased SpO2 IQR and lower SpO2 minima, and sixteen (28 %) exhibited an oscillatory pattern in VE and SpO2 without end-expiratory pauses. Twenty infants (35%) developed periodic breathing, associated with increased SpO2 IQR and lower SpO2 minima at the lowest FI O2 , 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. This article is protected by copyright. All rights reserved.