Simplified bedside assessment of pulmonary gas exchange in very preterm infants at 36 weeks' postmenstrual age.

Introduction We aimed to develop and validate a prediction table for a simplified measure of rightward shift of the fetal oxyhaemoglobin saturation (SpO2) versus inspired oxygen pressure (PIO2) curve as an objective marker of lung disease severity in very preterm infants, independent of unit altitude or oxygen prescribing policies. Methods Very preterm infants (n=219) had an oxygen reduction test at median (IQR) test age of 354 (345–360) weeks’ postmenstrual age (PMA). Shift was derived from at least three paired SpO2 versus PIO2 measurements using a computer algorithm, using the fetal oxyhaemoglobin dissociation curve as the reference. Linear regression of resultant shift values enabled construction of a table to predict shift using a single paired SpO2 versus PIO2 measurement, validated subsequently in a separate infant cohort using Bland-Altman analysis. Receiver operating curve analysis provided threshold values equating to a clinical diagnosis of mild bronchopulmonary dysplasia (BPD) or moderate to severe BPD. Results The median (IQR) age of 63 infants in the validation cohort was 360 (356–362) weeks’ PMA. Mean difference (95% CI) between predicted and measured shift was 2.1 (−0.8% to 4.9%) with wide limits of agreement (−20.7% to 24.8%). Predicted shift >10.1 kPa identified mild BPD with 71% sensitivity and 88% specificity while values>13.0 kPa identified moderate to severe BPD with 81% sensitivity and 100% specificity. Discussion Shift predicted from a single paired SpO2 versus PIO2 measurement using our validated table enables objective bedside screening of lung disease severity in very preterm infant cohorts at 36 weeks’ PMA.