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Inspired oxygen concentrations during positive pressure therapy
Elizabeth A Yoder1, Kenneth Klann, Kingman P Strohl
1Louis Stokes Cleveland DVA Medical Center, Medical Service, Center for Sleep Disorders Research, Case Western Reserve University, Cleveland, Ohio, USA. Beth.Yoder@att.net
Objectives:
This study examined the effects of various factors that might influence the fraction of oxygen in inspired air (FiO (2)) in a human and in a model system during nasal positive pressure treatments.
Design And Methods:
A healthy male volunteer and a mannequin head were each outfitted with a nasal continuous positive air pressure mask and pressure source (BiPAP S, Respironics, Murrysville, PA). Oxygen was added through either a side port in the mask or a port near the machine. Flow and FiO (2) were measured while varying inspiratory and expiratory pressures. Measurements were repeated with a leak added to the system and using different sites of oxygen administration.
Results:
In both the human and in the model system, increasing inspiratory pressure, thereby increasing flow, decreased FiO (2) inside the mask. In the model system, addition of a fixed leak caused an increase in flow and decrease in FiO (2) at any given level of inspiratory and expiratory pressure.
Conclusion:
In patients using nasal positive pressure therapy, variables of pressure, leak around the mask, and the site of oxygen delivery determine the inspired oxygen concentration when giving oxygen supplementation.
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