Oxygen injection site affects FIO2 during noninvasive ventilation

Abstract

Most portable bi-level positive airway pressure devices are not equipped with air-oxygen blenders for precisely regulating oxygen concentrations, and supplemental oxygen must be added to increase the FIO2. Very few studies have investigated the factors that affect FIO2, and their conclusions have been inconsistent. We investigated in vitro noninvasive ventilation (NIV) parameters and their effects on FIO2, particularly the effect of the oxygen injection site. Methods: NIV was simulated with a test lung and manikin setup. FIO2 was measured with 4 oxygen injection sites (mask, in front of the exhalation valve, at the humidifier outlet, and proximal to the ventilator), with 3 exhalation valve types, with 2 oxygen flows, and with 4 combinations of inspiratory and expiratory pressure. Results: Oxygen flow, inspiratory and expiratory pressure, and exhalation valve type all affected FIO2. For a given oxygen flow, the oxygen injection site was the most important factor that affected FIO2. The oxygen injection site that was closest to the patient (on the mask) had the higher FIO2 (P