Abstract
Background: Most portable bi-level positive airway pressure (BPAP) devices are not equipped with air-oxygen blenders for precisely regulating oxygen concentrations and supplemental oxygen must be added to increase the fraction of inspired oxygen (FiO2). Very few studies have investigated the factors that affect FiO2 and their conclusions were inconsistent. We investigated in vitro non-invasive positive pressure ventilator (NPPV) parameters and their effects on FiO2, particularly the effect of the oxygen injection site.
Methods: NPPV therapy in the spontaneous breathing mode was simulated using a simulation lung platform. FiO2 was measured after varying different parameters: oxygen injection site (mask, in front of exhalation valve, at the humidifier outlet, or proximal to the ventilator); exhalation valve type; oxygen flow; and inspiratory and expiratory pressures. General linear models were used to assess the effects of these experimental factors on oxygen concentration.
Results: The 4 variables of oxygen flow rate, inspiratory and expiratory pressure, and exhalation valve type, all affected the FiO2. Remarkably, for a given oxygen flow rate, the oxygen injection site was the most important factor that affected FiO2; an oxygen injection site that was closer to a patient resulted in a higher FiO2. The highest fraction of inspired oxygen was measured when the oxygen injection site was on the mask (P-values < 0.0001).
Conclusion: Among the various factors evaluated in this study, for a given oxygen flow rate, the oxygen injection site had the greatest effect on inspired oxygen concentration during NPPV.
- inspired oxygen concentration
- noninvasive positive pressure ventilation
- respiratory flow rate
- oxygen injection site
Footnotes
- Corresponding author: Jian Kang, MD; Department of Respiratory Medicine, the First Affiliated Hospital of China Medical University, Nanjing North Street No.155, Heping district, Shenyang, 110001, People’s Republic of China. Email: kangjian58{at}163.com; Fax: +86-24-25919606
Conflict of interest: None to declare.
Funding disclosure: None.
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