Accuracy of Pulse Oximetry for Long-Term Oxygen Therapy Assessment in Chronic Obstructive Pulmonary Disease.

Landmark studies of long-term oxygen therapy (LTOT) in patients with chronic obstructive pulmonary disease (COPD) used arterial oxygen pressure (Pa) to define severe hypoxemia; however, oxygen saturation as measured by pulse oximetry (Sp) is commonly used instead. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines recommend evaluation with arterial blood gas (ABG) analysis if Sp is ⩽92%. This recommendation has not been evaluated in stable outpatients with COPD undergoing testing for LTOT. To evaluate the performance of Sp compared with ABG analysis of Pa and arterial oxygen saturation (Sa) to detect severe resting hypoxemia in patients with COPD. Retrospective analysis of paired Sp and ABG values from stable outpatients with COPD who underwent LTOT assessment in a single center. We calculated false negatives (FNs) as an Sp >88% or >89% in the presence of pulmonary hypertension with a Pa ⩽55 mm Hg or ⩽59 mm Hg in the presence of pulmonary hypertension. Test performance was assessed using receiver operating characteristic (ROC) analysis, intraclass correlation coefficient (ICC), test bias, precision, and accuracy root-mean-square (A). An adjusted multivariate analysis was used to evaluate factors affecting Sp bias. Of 518 patients, the prevalence of severe resting hypoxemia was 74 (14.3%), with 52 missed by Sp (FN, 10%), including 13 (2.5%) with an Sp > 92% (occult hypoxemia). FNs and occult hypoxemia in Black patients were 9% and 1.5%, respectively, and were 13% and 5%, respectively, among active smokers. The correlation between Sp and Sa was acceptable (ICC = 0.78; 95% confidence interval, 0.74-0.81); and the bias of Sp was 0.45%, with a precision of 2.6 (-4.65 to +5.55%) and A of 2.59. These measurements were similar in Black patients, but in active smokers, correlation was lower and bias showed greater overestimation of Sp. ROC analysis suggests that the optimal Sp cutoff to warrant LTOT evaluation by ABG analysis is ⩽94%. Sp as the only measure of oxygenation carries a high FN rate in detecting severe resting hypoxemia in patients with COPD undergoing evaluation for LTOT. Reflex measurement of Pa by ABG analysis should be used as recommended by GOLD, ideally at a cutoff higher than an Sp ⩽92%, especially in active smokers.