Delivery of high inspired oxygen by face mask

We evaluated the ability of face masks (Hudson Oxygen Sales Co, Temeala, CA) to deliver high FIO₂ using a nonrebreathing mask (NRM) and a partial rebreathing mask (PRM). The PRM was studied with and without the addition of one or two sets of 50- and 100-mL tube extensions (tusks) added to the exhalation ports to decrease the volume of inspired room air. The FIO₂ was measured in the oropharynx in five subjects. It decreased with increasing minute ventilation and increased with increasing O₂ flow (15, 20, 30, and 60 L/min). At 60 L/min O₂ flow, FIO₂ was consistently greater than 0.8 and was independent of the minute ventilation or the type of mask used. At lesser O₂ flows, the FIO₂ was significantly less with the NRM than with the PRM (with or without tusks), presumably because of the resistance of the one-way inspiratory valve. With the PRM, at O₂ flows of 60 L/min, the addition of tusks did not significantly increase FIO₂. Significant improvement in FIO₂ occurred at 30 and 20 L/min O₂ flow with the addition of one or two sets of tusks while at an O₂ flow of 15 L/ min, only the addition of two sets of tusks improved the FIO₂. We conclude that it is possible to attain high FIO₂ by face mask, that the PRM delivers a higher FIO₂ than the NRM, and that tusks can improve the FIO₂ at lower O₂ flow rates. We also found that with an O₂ flow of 60 L/min, FIO₂ is high and independent of minute ventilation.