Influence of pulmonary factors on pulse oximeter saturation in preterm infants

© 2016, BMJ Publishing Group. All rights reserved.Aim: To describe how the stability of oxygen saturation measured by pulse oximetry (SpO2%) varies within and between infants with bronchopulmonary dysplasia (BPD). Methods: Clinically stable infants with BPD had SpO2 measured at different inspired oxygen concentrations (FIO2 expressed as %). A computer model of gas exchange, that is, ventilation/perfusion ratio (VA/Q) and shunt, plotted the curve of SpO2 versus FIO2 best fitting these data. The slope of this curve is the change in SpO2 per % change in FIO2, hence SpO2 stability, calculated at each SpO2 from 85% to 95%. Results: Data from 16 infants with BPD previously described were analysed. The dominant gas exchange impairment was low VA/Q (median 0.35, IQR, 0.16-0.4, normal 0.86). Median shunt was 1% (IQR, 0-10.5; normal <2%). Slope varied markedly between infants, but above 95% SpO2 was always