Inspired Oxygen Concentrations during Positive Pressure Therapy

Objectives: This study examined the effects of various factors that might influence the fraction of oxygen in inspired air (FiO₂) 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 FiO₂ 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 FiO₂ inside the mask. In the model system, addition of a fixed leak caused an increase in flow and decrease in FiO₂ 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.

Sleep apnea - treatment - CPAP - oxygen

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