P161 Predictors of in-flight desaturation and need for supplementary oxygen therapy during air travel. Hypoxic challenge test (HCT) in patients with chronic obstructive pulmonary disease (COPD) [Preliminary Results]

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Introduction and Objectives Patients with COPD planning air travel need careful evaluation by a lung specialist. According to current practice, baseline oxygen saturation and dyspnea are the initial screening tools, followed by a 6-min walking test to direct the need for an HCT. However, an HCT is time-consuming, not widely available in daily clinical practice and an indication for a HCT should be carefully sought. We hypothesized that pulmonary function tests (spirometry, body plethysmography, single-breath gas transfer), including oscillometry, a test that requires minimal patient co-operation, can reliably predict a significant desaturation during air travel, and therefore direct the need for an HCT. Methods Patients with stable COPD were recruited. Dyspnea was assessed by the mMRC scale, baseline SpO2 was measured, followed by a full pulmonary function testing and a 6MWT. The following functional parameters were evaluated: spirometry (FEV1, FVC, FEV1/FVC ratio), static volumes (TLC, FRC), diffusion capacity (DLCO), oscillometry [R5, R20, R5-R20, X5, Ax, Resonant frequency (Fres)]. All patients underwent HCT using a 40% Venturi mask with nitrogen as the driving gas (FiO2:15%) for 20 minutes or until SpO2<85%. A drop of SpO2<85% was considered as positive HCT. Results 15 patients were analyzed (67.9±6.5 years old). 4 (~26%) exhibited a significant desaturation in HCT. Based on ROC curve analysis, FEV1 showed the highest discriminatory ability for a positive HCT test (AUC=0.943, p<0.001), followed closely by Fres (AUC=0.925, p<0.001) and DLCO (AUC=0.926, p<0.001). Baseline SpO2 and SpO2 after 6-MWT showed excellent accuracy (both AUC=0.909, p<0.001) and the mMRC score had a good predictive value (AUC=0.864, p<0.001). Adding oscillometry parameters (Fres) to conventional lung function testing (FEV1, DLCO, mMRC and baseline SpO2) improved the correlation with SpO2 during the HCT test, as assessed by multiple regression analysis (adj R2=0.77, p=0.022, including oscillometry vs adj R2=0.62, p=0.027 without oscillometry). No significant effects were observed for lung volume measurements. Conclusions FEV1 exhibited the highest predictive value for a significant desaturation during an HCT and therefore, a low FEV1 should be actively sought during a pre-flight assessment in patients with COPD. Oscillometry improves the performance of conventional function testing in a preflight respiratory screening.

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