Ambulatory pulse oximetry monitoring in Japanese COPD outpatients not receiving oxygen therapy

BACKGROUND: It remains unknown whether desaturation profiles during daily living are associated with prognosis in patients with chronic obstructive pulmonary disease (COPD). Point measurements of resting oxygen saturation by pulse oximetry (SpO(2)) and partial pressure of arterial oxygen (PaO(2)) are not sufficient for assessment of desaturation during activities of daily living. A small number of studies continuously monitored oxygen saturation throughout the day during activities of daily living in stable COPD patients. This study aims to analyse the frequency of desaturation in COPD outpatients, and investigate whether the desaturation profile predicts the risk of exacerbation. METHODS: We studied stable COPD outpatients not receiving supplemental oxygen therapy. Baseline assessments included clinical assessment, respiratory function testing, arterial blood gas analysis, body mass index, and the COPD Assessment Test (CAT). Patients underwent 24-hour ambulatory monitoring of SpO(2) during activities of daily living. Exacerbations of COPD and death from any cause were recorded. RESULTS: Fifty-one patients were enrolled in the study, including 12 current smokers who were excluded from the analyses in case high serum carboxyhaemoglobin concentrations resulted in inaccurately high SpO(2) readings. The mean percent predicted forced expiratory volume in one second (%FEV(1)) was 50.9%. The mean proportion of SpO(2) values below 90% was 3.0% during the day and 7.4% during the night. There were no daytime desaturators, defined as ≥ 30% of daytime SpO(2) values below 90%. Twenty-one exacerbations occurred in 13 patients during the mean follow-up period of 26.4 months. Univariate and multivariate Cox proportional hazards analyses did not detect any significant factors associated with exacerbation. CONCLUSIONS: Our 24-hour ambulatory oximetry monitoring provided precise data regarding the desaturation profiles of COPD outpatients. Both daytime and nighttime desaturations were infrequent. The proportion of ambulatory SpO(2) values below 90% was not a significant predictor of exacerbation.