S93 Computed tomography (CT) derived estimates of total lung volume in patients with severe lung disease

Abstract

Introduction Total Lung capacity (TLC) is often measured in patients with advanced lung disease to help inform diagnosis, severity and management. However, some may not manage or tolerate the technical aspects of the gold standard test: whole body plethysmography (Pleth-TLC). N2 washout (N2W-TLC) is often used in lieu but it is unreliable in obstructive conditions and some still find it challenging. As all potential lung transplant candidates undergo thoracic CT during their workup, we hypothesised that CT estimates of total lung volume (CT-TLV) could substitute Pleth-TLC and are superior to N2W-TLC. Methods Prospectively collected data between April 2015–2018. 1–2 mm CT slices were analysed using Vitrea software (version 6.1.1169.10077, Vital Solutions, Toshiba Medical Systems Europe) by a single radiologist. Descriptive statistics were compared with parametric tests. Agreement and bias between methods were examined with Pearson’s correlation and Bland and Altman analysis. Results 202 patients were studied (94 female, mean [SD] age 52 [11] yrs, BMI 25.0 [4.2] kg/m2, COPD/IPF/CF/other n=72/45/21/64). 37 (18.3%) and 50 (24.8%) were unable to perform Pleth and N2W respectively. Paired data were available for comparison of CT vs Pleth (n=160), CT vs N2W (147) and Pleth vs N2W (131), with subgroup analysis into obstructive, restrictive and normal ventilation. Mean [SD] CT-TLV, Pleth-TLC and N2W-TLC were 4.69 [1.95], 5.20 [2.06] and 4.32 [1.71] L respectively, p Conclusion CT estimates of TLC reliably approximate Pleth-TLC and could replace body box measurement in practice, for patient convenience and cost containment. Gastro-oesophageal air, captured by Pleth but not CT, accounts for some of the underestimation. The consistent small bias with a reliable homoscedastic difference between these methods may allow incorporation of a correction factor and wider application of this CT algorithm.