Predicting the need for supplemental oxygen during airline flight in patients with chronic pulmonary disease: a comparison of predictive equations and altitude simulation

Abstract

Background: Patients with chronic pulmonary diseases are at increased risk of hypoxemia when travelling by air. Screening guidelines, predictive equations based on ground level measurements and altitude simulation laboratory procedures have been recommended for determining risk but have not been rigorously evaluated and compared.

Objectives: To determine the adequacy of screening recommendations that identify patients at risk of hypoxemia at altitude, to evaluate the specificity and sensitivity of published predictive equations, and to analyze other possible predictors of the need for in-flight oxygen.

Methods: The charts of 27 consecutive eligible patients referred for hypoxia altitude simulation testing before flight were reviewed. Patients breathed a fraction of inspired oxygen of 0.15 for 20 min. This patient population was compared with the screening recommendations made by six official bodies and compared the partial pressure of arterial oxygen (PaO(2)) obtained during altitude simulation with the PaO(2) predicted by 16 published predictive equations.

Results: Of the 27 subjects, 25% to 33% who were predicted to maintain adequate oxygenation in flight by the British Thoracic Society, Aerospace Medical Association or American Thoracic Society guidelines became hypoxemic during altitude simulation. The 16 predictive equations were markedly inaccurate in predicting the PaO(2) measured during altitude simulation; only one had a positive predictive value of greater than 30%. Regression analysis identified PaO(2) at ground level (r=0.50; P=0.009), diffusion capacity (r=0.56; P=0.05) and per cent forced expiratory volume in 1 s (r=0.57; P=0.009) as having predictive value for hypoxia at altitude.

Conclusions: Current screening recommendations for determining which patients require formal assessment of oxygen during flight are inadequate. Predictive equations based on sea level variables provide poor estimates of PaO(2) measured during altitude simulation.

Figures

Figure 1)

Partial pressure of arterial oxygen (PaO2) drop in six patients whom guidelines considered fit to fly. The patients were considered fit to fly by at least one of the criteria set by the British Thoracic Society (BTS; baseline saturation of peripheral oxygen [SpO2] >95% and the Aerospace Medical Association (AMA; PaO2 at ground level ≥70 mmHg). Three patients had a posthypoxia altitude simulation test (HAST) PaO2 of less than 50 mmHg, while the other three subjects had a PaO2 of between 50 mmHg and 55 mmHg

Figure 2)

Receiver operating characteristic (ROC) analysis of baseline partial pressure of arterial oxygen (PaO2) and resting baseline saturation of peripheral oxygen (SpO2) related to the hypoxia altitiude simulation test (HAST) outcome (n=27). (A) ROC curve of PaO2 at ground level and HAST outcome gave an area under the curve of 0.696 (P=0.13). At a specificity of 100, PaO2 ≤72 mmHg. (B) ROC analysis of SpO2 at rest related to HAST outcome, gave an area under the curve of 0.402 and a SpO2 cut-off for recommending a HAST of 95% or lower