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 cmH₂O 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 (R²=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.