Validation of pre-flight algorithms in predicting hypoxic challenge testing (HCT) outcomes in interstitial lung disease (ILD).

Abstract

Background: The British Thoracic Society (BTS) currently recommends pre-flight clinical assessment of all symptomatic patients with interstitial lung disease (ILD). This may include hypoxic challenge testing (HCT) to determine whether supplemental in-flight oxygen is required, but it is not universally available.

Objectives: (1) To validate a previously published pre-flight assessment algorithm in predicting outcomes of HCT in ILD. (2) Compare the sensitivity and specificity of the original algorithm to an amended version published in the BTS clinical statement on air travel.

Design: Single centre, cohort study.

Methods: A single-centre retrospective cohort analysis of ILD patients attending for HCT between March 2017 and April 2023.

Results: A total of 126 patients with a diagnosis of ILD underwent HCT. Median forced vital capacity 75.0% predicted (interquartile range (IQR) 24.8) and transfer factor for carbon monoxide 45.8% predicted (IQR 18.6). Diagnosis of idiopathic pulmonary fibrosis in 50.8% (n = 64). A total of 18 individuals became hypoxic during the test (a fall of PaO₂ to <6.6 kPa or oxygen saturations (SpO₂) < 85% pO₂, 'failed HCT'). The pre-flight algorithm demonstrated moderate sensitivity (69.4%, identifying most 'passed' cases correctly, 43/62) and good specificity (83.3%, most 'failed' cases correctly identified, 10/12). A total of 52 (41.2%) patients would have been referred for HCT, with 11.5% (n = 6) requiring in-flight oxygen ('failed' HCT). The modified BTS algorithm demonstrated a moderate sensitivity of 70.3% (45/64) and good specificity of 83.3% (10/12). In both algorithms, 29 patients would have been advised in-flight oxygen, whilst only 10 of these required supplementary oxygen according to HCT. There were two divergences in algorithmic outcomes, both arising from patients without desaturation on exercise, resulting in two fewer HCT using the BTS algorithm and correctly advising 'no supplemental oxygen' was required.

Conclusion: In this validation study, the practical pre-flight algorithm demonstrates good specificity and moderate sensitivity for predicting HCT outcomes. The BTS modified algorithm demonstrates comparable sensitivity and specificity. Additional work is required to further develop practical guidance to reduce both the number of HCT advised and the proportion of patients incorrectly advised to arrange supplemental in-flight oxygen.