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Ambulatory Oximetry Monitoring in Patients With Severe COPD^*

A Preliminary Study

^* From the Veterans Affairs Medical Center (Dr. Pilling), Pulmonary Disease Division, Department of Medicine, Brown University School of Medicine, Providence, RI; and the Veterans Affairs Medical Center (Dr. Cutaia), Research Service, Pulmonary Disease Division, University of Pennsylvania, Philadelphia, PA.

Correspondence to: Michael Cutaia, MD, FCCP, Veterans Affairs Medical Center, Research Service, Pulmonary Disease Division, University of Pennsylvania, Philadelphia, PA 19104; e-mail: mcutaia{at}mail.med.upenn.edu

Background: The benefits of long-term oxygen supplementation in COPD patients with hypoxemia are well established. The standard approach to prescribing oxygen uses a static assessment of oxygen requirements in a hospital or clinic setting. The assumption behind this approach is that patients will maintain a "therapeutic" hemoglobin oxygen saturation (SpO₂) in the outpatient setting. We questioned the validity of this assumption, and hypothesized that many patients may demonstrate significant oxygen desaturation during normal activities of daily living.

Study design, methods, and measurements: We determined if oxygen supplementation maintained a therapeutic SpO₂ level in patients with COPD (n = 27), using the technique of ambulatory oximetry monitoring (AOM). AOM consisted of using a portable oximeter to monitor SpO₂, pulse rate, and patient activity while patients were engaged in normal activities of daily living over an extended time period (~18 h). The portable oximeter collected and stored these data every 15 s over the monitored time period. Each AOM recording was manually scored for desaturation events and other key variables, including average SpO₂ over the monitoring period, the average number of desaturation events per hour, and the percentage of monitored time deleted secondary to artifacts.

Setting: University-affiliated Veterans Affairs Medical Center.

Patients: All subjects were patients with stable COPD with no recent history of hospitalization or exacerbation of their lung disease.

Results:This cohort of patients demonstrated a surprising frequency of desaturation below the recommended target SpO₂ value (90%), which averaged approximately 25% of AOM recording time. There was wide variability among patients in the percentage of time SpO₂ was below the target value (range, 3 to 67% of AOM recording time). Motion artifact on the AOM recordings was not a major problem; an average of 8% of the recording time was deleted secondary to artifacts in this patient cohort.

Conclusions: The results demonstrate that AOM is feasible and accurate with an acceptable level of motion artifact. These results also suggest that the standard approach for prescribing oxygen may lead to subtherapeutic SpO₂ values in the outpatient setting. AOM holds promise as a tool to monitor the adequacy of oxygen prescriptions in the outpatient setting in patients with lung disease.

Key Words: ambulatory oximetry monitoring • COPD • long-term oxygen therapy

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