Ambulatory oximetry monitoring in patients with severe COPD - A preliminary study

Background: The benefits of long-term oxygen supplementation in COPD patien ts with hyposemia are well established, The standard approach to prescribin g oxygen uses a static assessment of oxygen requirements in a hospital or c linic setting, The assumption behind this approach is that patients will ma intain a "therapeutic" hemoglobin oxygen saturation (SpO(2)) in the outpati ent setting, We questioned the validity of this assumption, and hypothesize d that many patients may demonstrate significant oxygen desaturation during normal activities of daily living, Study design, methods, and measurements:We determined if oxygen supplementa tion maintained a therapeutic SpO(2) level in patients with COPD (n = 27), using the technique of ambulatory oximetry monitoring (AOM). AOM consisted of using a portable oximeter to monitor SpO(2), poise rate, and patient act ivity while patients were engaged in normal activities of daily living over an extended time period (similar to 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 variabl es, including average SpO(2) over the monitoring period, the average number of desaturation events per hour, and the percentage of monitored time dele ted secondary to artifacts, Setting: University-affiliated Veterans Affairs Medical Center, Patients: All subjects were patients with stable COPD with no recent histor y of hospitalization or exacerbation of their lung disease. Results: This cohort of patients demonstrated a surprising frequency of des aturation below the recommended target SpO(2) value (90%), which averaged a pproximately 25% of AOM recording time. There was wide variability among pa tients in the percentage of time SpO(2), 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 se condary 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 th e standard approach for prescribing oxygen may lend to subtherapeutic SpO(2 ), 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.