Background: Oxygen masks with reservoir bags (OMR) are widely used for oxygen therapy in patients with severe respiratory failure. The purpose of the present study was to determine whether OMRs are effectively used in clinical practice.
Methods and results: In the first phase of the study on the patients with severe respiratory failure, no apparent respiratory motions of the reservoir bag were noted, and the oxygen saturation level as determined by pulseoximetry (SpO2) did not decrease even after shrinkage of the reservoir bag. In the second phase, when a healthy female volunteer wore an OMR, pressure swings in the reservoir bag were less than 0.1 cmH2O, even when she was breathing with her maximal respiratory efforts (tidal volume, 1.14 L and respiratory frequency, 19.2 bpm). These pressure swings provoke a less than 50 mL oxygen supply from the reservoir bag. The decreased efficacy of OMR in oxygen therapy may be primarily due to the large space between the OMR and the nose but this space is inevitable in sitting or orthopneic subjects.
Conclusions: Fixing an OMR very tightly to the face is mandatory for its effective use. It should also be kept in mind that there are limitations to the efficacy of OMR, even when they are used with such careful management.