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.

KEYWORDS

Sleep apnea - treatment - CPAP - oxygen

REFERENCES

• 1 Kita H, Ohi M, Chin K et al.. Effects of nasal continuous positive airway pressure therapy on respiratory parameters of upper airway patency in patients with obstructive sleep apnea syndrome.  Chest. 1998;  114 691-696
• 2 Naughton M T. Pathophysiology and treatment of Cheyne-Stokes respiration.  Thorax. 1998;  53 514-518
• 3 Resta O, Guido P, Picca V et al.. Prescription of nCPAP and nBIPAP in obstructive sleep apnoea syndrome: Italian experience in 105 subjects. A prospective two centre study.  Respir Med. 1998;  92 820-827
• 4 Schafer H, Ewig S, Hasper E, Luderitz B. Failure of CPAP therapy in obstructive sleep apnoea syndrome: predictive factors and treatment with bilevel-positive airway pressure.  Respir Med. 1998;  92 208-215
• 5 Sampol G, Sagales M T, Roca A, de la Calzada M D, Bofill J M, Morell F. Nasal continuous positive airway pressure with supplemental oxygen in coexistent sleep apnoea-hypopnoea syndrome and severe chronic obstructive pulmonary disease.  Eur Respir J. 1996;  9 111-116
• 6 Teschler H, Stampa J, Ragette R, Konietzko N, Berthon-Jones M. Effect of mouth leak on effectiveness of nasal bilevel ventilatory assistance and sleep architecture.  Eur Respir J. 1999;  14 1251-1257