Twenty-four-hour ambulatory oximetry monitoring in COPD patients with moderate hypoxemia.

BACKGROUND: The relationship of diurnal desaturations (oximetry-measured blood oxygen saturation [S(pO(2))] < 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 [FEV(1)] < 80% of predicted, ratio of FEV(1) to forced vital capacity < 70% of predicted, and P(aO(2)) 60-70 mm Hg) with 24 hours of ambulatory oximetry. Desaturators were defined as those who spent >/= 30% of the time with S(pO(2)) < 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(aCO(2)) (p = 0.001) and lower P(aO(2)) (p = 0.007) than the nondesaturators. There were no differences in the other variables. The correlation between nocturnal and diurnal time with S(pO(2)) < 90% was r(2) = 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.