The Oxygen Delivery Characteristics of the Hudson Oxy-one Face Mask

The inspired oxygen fraction (F_IO₂) delivered by the Hudson Oxy-one face mask was measured under changing conditions of ventilation, oxygen flow rate to mask, and mask fit. A single trained subject sat in a body plethysmograph to measure ventilation and breathed at a constant rate of 15 per minute at three different tidal volumes, of approximately 0.3, 0.6, and 1.2 litres, from the mouthpiece in the plethysmograph. The Oxy-one face mask was fitted to a plaster-of Paris face model on the outside of the plethysmograph in a loose and then in a tight fashion. Oxygen concentration was continuously monitored from a point in the metal tube connecting the face model to the mouthpiece.

The tightly fitting mask demonstrated an orderly reduction in F_IO₂ as ventilation increased and oxygen flow rate to the mask decreased. The mean F_IO₂ at a ventilation of 4.5 l.min^-1 and 8 l.min^-1 oxygen flow was 78% and this fell to 27% at a ventilation of 16 l.min^-1 and oxygen flow of 2 l.min^-1. The loosely fitting mask demonstrated larger SD of measurements and lower mean maximum F_IO₂ values of 46 to 49% and these fell in an irregular fashion to similar minimum values as ventilation increased and oxygen flow decreased.

Although the precise definition of the F_IO₂ for each breath from the changing concentration during each inspiration was not possible, these results indicate that F_IO₂ changes in a predictable way as a function of ventilation and oxygen flow, if the mask is close fitting. This method could be conveniently used to study other oxygen delivery systems.