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

Abstract

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 (P_IO₂) 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 P_IO₂ 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 P_IO₂ 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 P_IO₂ measurement using our validated table enables objective bedside screening of lung disease severity in very preterm infant cohorts at 36 weeks' PMA.

Keywords: lung physiology; paediatric lung disaese.