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Employing the Forced Oscillation Technique for the Assessment of Respiratory Mechanics in Adults
Published on: February 9, 2022
External validation of predictive equations for determining the need for in-flight oxygen supplementation in patients
Murielle Emma Beaupré1, Gao Sheng Huang1, Bruno-Pierre Dubé1,2
1Service de Pneumologie, Centre Hospitalier de l'Université de Montréal (CHUM), Université de Montréal, Montreal, QC, Canada.
Rationale:
Patients with chronic respiratory diseases may develop clinically significant hypoxemia during commercial air travel because of reduced cabin pressure. In-flight oxygen prescription is typically guided by hypoxic challenge testing (HCT), a procedure that is time-consuming, costly, and not universally available. Several predictive equations based on sea-level physiological measurements have been proposed as alternatives. We aimed to externally validate six published predictive equations by comparing their performance with HCT in a large, heterogeneous cohort of patients with chronic respiratory diseases.
Methods:
We retrospectively analyzed all patients who underwent HCT at our center between 2016 and 2026. Sea-level arterial blood gases, pulmonary function tests, and relevant clinical data were collected. Six published predictive equations (E1-E6) were used to estimate in-flight PaO2 and compared with PaO2 measured during HCT.
Results:
A total of 177 patients were included: 39 (22%) with COPD, 64 (36%) with ILD, 34 (19%) with cystic fibrosis, and 40 (23%) with other chronic respiratory diseases. Significant correlations between predicted in-flight PaO2 and HCT PaO2 were observed (ρ = 0.48 for E1 and E2 to 0.84 for E5; all p ≤ 0.001), but diagnostic performance remained limited. Across all patients, predictive equations demonstrated high specificity (76% for E2 to 98% for E6) but inadequate sensitivity (11% for E6 to 67% for E2) for identifying patients requiring supplemental oxygen. Cohen's κ coefficients ranged from 0.07 (95% CI, -0.06 to 0.20) for E4 to 0.43 (95% CI, 0.27-0.59) for E2. Areas under the ROC curve ranged from 0.71 (95% CI, 0.62-0.81) for E4 to 0.79 (95% CI, 0.70-0.88) for E1.
Conclusions:
In this large external validation study, currently available predictive equations demonstrated insufficient diagnostic performance to safely replace HCT for determining the need for in-flight oxygen supplementation. Although several equations showed moderate to strong agreement with measured HCT PaO2, inadequate sensitivity resulted in clinically important misclassification of patients requiring supplemental oxygen. HCT should remain the reference standard for evaluating patients in whom the need for in-flight oxygen supplementation is uncertain.
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