A demand valve conserves oxygen in subjects with chronic obstructive pulmonary disease

Demand valves conserve oxygen by limiting delivery to the inspiratory phase of respiration and reducing the waste which occurs during expiration with conventional, constant flow therapy. However, arterial oxygen tensions (PaO2) achieved in past evaluations were frequently higher than recommended for treating chronic hypoxemia. We wondered if excessive amounts of oxygen were used which would exaggerate waste with conventional therapy, and, in turn, apparent savings with demand valves. Oxygen savings were evaluated with a demand valve in ten stable COPD patients who had recommended levels of PaO2 (55 to 65 mm Hg, SaO2 90 percent to 92 percent). The valve reduced oxygen use significantly compared to conventional therapy (average savings 28 percent, range 14 percent to 49 percent). The greatest savings were found in subjects who used the highest conventional flows.