Mediastinal Shift Index: A Novel Postnatal Measurement of Mediastinal Movement that Predicts Survival in Neonates With Congenital Diaphragmatic Hernia on Extracorporeal Membrane Oxygenation

Mediastinal position varies in neonates with congenital diaphragmatic hernia (CDH), reflecting contralateral shift due to mass effect. We aimed to create and validate a postnatal measurement of mediastinal positioning using chest radiographs in neonates with CDH who require extracorporeal membrane oxygenation. Chart review identified neonates with CDH who required veno-arterial extracorporeal membrane oxygenation between 2017 and 2022. Mediastinal shift index (MSI) is the ratio of the distance between the venous cannula tip and the contralateral chest wall divided by the total width of the contralateral hemithorax. Three raters completed MSI measurements at designated timepoints: after cannulation, post- CDH repair, and immediately before decannulation. Intraclass correlation coefficients (ICC) assessed inter-rater agreement. Initial MSI and observed/expected lung head ratio (O/E LHR) were correlated and compared between survivors and non-survivors. Receiver operative characteristic (ROC) curve analysis evaluated the ability of MSI and O/E LHR to predict survival. 38 neonates were included. MSI demonstrated excellent agreement (ICC>0.98) amongst raters. Initial MSI and O/E LHR had a moderate positive correlation (Spearman correlation = 0.47, p = 0.014). Initial MSI differed significantly between survivors and non-survivors (0.52 vs. 0.33, p = 0.035) as did O/E LHR (0.36 vs. 0.26, p = 0.036). ROC analysis revealed initial MSI >0.35 was predictive of survival with 73% sensitivity and 70% specificity. Mediastinal shift index is reliable and predicted survival with a higher specificity than O/E LHR. Future studies will elucidate the role of trending MSI over a patient's course to inform interventions to optimize mediastinal position. 3.