Early respiratory system reactance predicts respiratory outcomes in preterm infants: a retrospective, multicentre study

Objective This multicenter, international, retrospective study aims to investigate whether respiratory system reactance (Xrs) assessed by respiratory oscillometry on the 7th day of life is associated with respiratory outcomes in preterm infants below 32 weeks’ gestation. Methods Sinusoidal pressure oscillations (2–5 cmH 2 O peak-to-peak, 10 Hz) were superimposed on the positive end-expiratory pressure (PEEP). We assessed the association of Xrs z-score with the duration of respiratory support using linear regression and with bronchopulmonary dysplasia (BPD, according to Jensen et al . 2019) using logistic regression. We used the likelihood ratio test to evaluate whether Xrs z-score adds significantly to clinical predictors, including gestational age (GA), birth weight (BW) and the National Institute of Child Health and Human Development (NICHD) BPD prediction model. Results One hundred and thirty-seven infants (median (Q1, Q3) GA=28.43 (26.11, 30.29) weeks) were included; 44 (32%) developed BPD. Xrs z-score was significantly associated with the duration of respiratory support (R 2 =0.35). Xrs z-score was significantly higher in infants who developed BPD (p<0.001); the optimal cut-off value was 2.6, associated with 77% sensitivity and 80% specificity. In univariable analysis, per z-score increase in Xrs, the OR for BPD increased by 60% and the respiratory support by eight days. In multivariable analysis, Xrs z-score added significantly to the NICHD model and to GA and BW z-score to predict respiratory support duration (p=0.016 and p=0.014, respectively) and BPD development (p=0.003 and p<0.001, respectively). Conclusion Xrs z-score on the 7th day after birth improves the prediction of respiratory outcome in preterm infants.