Validation of Noninvasive Assessment of Pulmonary Gas Exchange in Patients with Chronic Obstructive Pulmonary Disease during Initial Exposure to High Altitude.

Investigation of pulmonary gas exchange efficacy usually requires arterial blood gas analysis (aBGA) to determine arterial partial pressure of oxygen (mPaO 2 ) and compute the Riley alveolar-to-arterial oxygen difference (A-aDO 2 ); that is a demanding and invasive procedure. A noninvasive approach (AGM100), allowing the calculation of PaO 2 (cPaO 2 ) derived from pulse oximetry (SpO 2 ), has been developed, but this has not been validated in a large cohort of chronic obstructive pulmonary disease (COPD) patients. Our aim was to conduct a validation study of the AG100 in hypoxemic moderate-to-severe COPD. Concurrent measurements of cPaO 2 (AGM100) and mPaO 2 (EPOC, portable aBGA device) were performed in 131 moderate-to-severe COPD patients (mean ±SD FEV 1 : 60 ± 10% of predicted value) and low-altitude residents, becoming hypoxemic (i.e., SpO 2 < 94%) during a short stay at 3100 m (Too-Ashu, Kyrgyzstan). Agreements between cPaO 2 (AGM100) and mPaO 2 (EPOC) and between the O 2 -deficit (calculated as the difference between end-tidal pressure of O 2 and cPaO 2 by the AGM100) and Riley A-aDO 2 were assessed. Mean bias (±SD) between cPaO 2 and mPaO 2 was 2.0 ± 4.6 mmHg (95% Confidence Interval (CI): 1.2 to 2.8 mmHg) with 95% limits of agreement (LoA): -7.1 to 11.1 mmHg. In multivariable analysis, larger body mass index ( p = 0.046), an increase in SpO 2 ( p < 0.001), and an increase in PaCO 2 -PETCO 2 difference ( p < 0.001) were associated with imprecision (i.e., the discrepancy between cPaO 2 and mPaO 2 ). The positive predictive value of cPaO 2 to detect severe hypoxemia (i.e., PaO 2 ≤ 55 mmHg) was 0.94 (95% CI: 0.87 to 0.98) with a positive likelihood ratio of 3.77 (95% CI: 1.71 to 8.33). The mean bias between O 2 -deficit and A-aDO 2 was 6.2 ± 5.5 mmHg (95% CI: 5.3 to 7.2 mmHg; 95%LoA: -4.5 to 17.0 mmHg). AGM100 provided an accurate estimate of PaO 2 in hypoxemic patients with COPD, but the precision for individual values was modest. This device is promising for noninvasive assessment of pulmonary gas exchange efficacy in COPD patients.