Lung Volume Predicts Survival and Diaphragm Plications on ILD Patients Undergoing Transplant Using Frustum Model
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PURPOSE: To validate the frustum model for lung volumes in patients with interstitial lung disease (ILD) undergoing lung transplantation, and to test whether lung size by frustum model is associated with cumulative survival advantage and need for diaphragm plication following lung transplant. METHOD: This retrospective observational study consisted of 180 patients seen in the University of Texas Southwestern-affiliated hospitals during the period from May 2010 to May 2016. Patients receiving bilateral or single lung transplant for ILD with available pre and post-operative CT scans were included. Bilateral lung transplants were performed through thoracosternotomy and single lung transplants through a unilateral thoracotomy. Cardiopulmonary bypass was used in 48% of patients. The frustum equation for a truncated cone was used to calculate total lung volume with pre and post-operative CT and XR chest PA closest to surgery time. Lung height was defined as the distance from the first rib to the diaphragm on XR chest. Radius 1 and 2 were obtained with same landmarks on CT scan. Patients were stratified by post/pre transplant lung volume ratio >1 or ratio ≤ 1. Multivariate logistic regression analysis and Cox proportional hazards regression models were used for statistical analysis of diaphragm plication and overall survival. RESULTS: Of the total 180 patients included, 39 (22%) had lung volume ratio ≤1 and 141 (78%) had ratio > 1. To validate the frustum model, a Pearson Correlation Coefficient was used to assess correlation between plethysmography TLC and frustum volume (n =251, r=.85, p <.01). Multivariate analysis for diaphragm plication included lung ratio, BMI, and smoking status. Lung volume ratio was a significant predictor of diaphragm plication (ratio >1 OR 7.19, p <.05). Multivariable Cox regression model for survival included lung ratio, diabetes, dyslipidemia, reintubation, and post-operative pneumonia. The only significant predictors were lung ratio (ratio ≤1HR 1.79, p <.05) and reintubation (HR 3.43, p<.01). CONCLUSION: The frustum model is a valid method for evaluating lung volumes in transplantation. The study suggests that lung volume confirms previous observations of a survival advantage to larger donor size in ILD. However, larger lung size may require diaphragm plication.