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

Background This multicentre, international, retrospective study aimed to investigate whether respiratory system reactance ( X rs ) assessed by respiratory oscillometry on day 7 of life is associated with respiratory outcomes in preterm infants below 32 weeks gestational age (GA). Methods Sinusoidal pressure oscillations (2–5 cmH 2 O peak-to-peak, 10 Hz) were superimposed on the positive end-expiratory pressure. We assessed the association of X rs z-score with the duration of respiratory support using linear regression and with bronchopulmonary dysplasia (BPD) using logistic regression. We used the likelihood ratio test to evaluate whether X rs z-score adds significantly to clinical predictors, including GA, birthweight (BW) and the National Institute of Child Health and Human Development (NICHD) BPD prediction model. Results 137 infants (median (interquartile range) 28.43 (26.11–30.29) weeks GA) were included; 44 (32%) developed BPD. X rs z-score was significantly associated with the duration of respiratory support (R 2 =0.35). X rs 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 X rs , the odds ratio for BPD increased by 60% and the respiratory support by 8 days. In multivariable analysis, X rs 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 X rs z-score on the 7th day after birth improves the prediction of respiratory outcome in preterm infants.