Twenty-Four-Hour Ambulatory Oximetry Monitoring in COPD Patients With Moderate Hypoxemia

BACKGROUND: The relationship of diurnal desaturations (oximetry-measured blood oxygen saturation [S_pO2] < 90%) during activities of daily living and clinical aspects in patients with chronic obstructive pulmonary disease (COPD) and moderate hypoxemia has not been systematically evaluated.

METHODS: We prospectively studied 88 patients with stable COPD (forced expiratory volume in the first second [FEV₁] < 80% of predicted, ratio of FEV₁ to forced vital capacity < 70% of predicted, and P_aO2 60–70 mm Hg) with 24 hours of ambulatory oximetry. Desaturators were defined as those who spent ≥ 30% of the time with S_pO2 < 90%. Patients engaged in their usual activities of daily living. We correlated these desaturations with the following variables, measured immediately before the 24 hours of oximetry: body mass index, dyspnea (measured with the modified Medical Research Council dyspnea scale), gas exchange, pulmonary function, quality of life (measured with the Saint George's respiratory questionnaire), and comorbidity (measured with the Charlson index).

RESULTS: Thirty-three (38%) of the patients were desaturators: 50% nocturnal and 22% diurnal. We also measured daytime arterial blood gas values from arterial blood samples and found that the desaturators had higher P_aCO2 (p = 0.001) and lower P_aO2 (p = 0.007) than the nondesaturators. There were no differences in the other variables. The correlation between nocturnal and diurnal time with S_pO2 < 90% was r² = 0.67, and the concordance was low (Cohen's kappa 0.43, p < 0.001).

CONCLUSIONS: Patients with stable COPD and moderate hypoxemia have frequent and potentially important desaturations during activities of daily living and at night. In addition, there is a big difference in the profile and degree of nocturnal and diurnal desaturations. Twenty-four hours of oximetry provides valuable information for comprehensive evaluation of patients with COPD.