[Effect of oxygen tubing connection site, changes of the inspiratory positive airway pressure and tidal volume on inspired oxygen concentration during noninvasive positive pressure ventilation].

Objective We evaluated the effects of administering oxygen through nasal catheter inside the mask or through the mask on inspired oxygen concentration in order to find better ways of administering oxygen to improve the inspired oxygen concentration in non-invasive positive pressure ventilation (NPPV). Methods A human face model was used to simulate the human face, and the model of the double lumen endotracheal tube was used to simulate the bilateral nasal cavity and trachea, and then a model was constructed to allow simulated NPPV. The changes of FIO2 were measured in different pressure (constant tidal volume) and different tidal volume (constant pressure) conditions under the way of administering oxygen through nasal catheter inside the mask or through the mask. The effects on FIO2 were measured in different pressure (constant tidal volume) and different tidal volume (constant pressure) conditions under same way of administering oxygen. Results The FIO2 was (35.4±1.7)% when oxygen was administered through the mask, but a higher FIO2 was achieved with the oxygen injected into the mask[(52.4±2.1)%, and oxygen flow of 5 L/min, P<0.05]. The oxygen concentration declined with the increase of inspiratory positive airway pressure (IPAP) on the condition of administering oxygen through the mask on constant tidal volume. The FIO2 at IPAP 16 cmH2O (1 cmH2O=0.098 kPa) was higher than that at IPAP 8 cmH2O, and the FIO2 at IPAP 20 cmH2O was higher than those at IPAP 8 cmH2O and 12 cmH2O, P<0.05. The oxygen concentration increased with the tidal volume increase on the condition of administering oxygen through the mask on constant IPAP. The changes of tidal volume and IPAP had no effects on FIO2 on the condition of administering oxygen through nasal catheter inside the mask. Conclusions Administering oxygen through nasal catheter inside the mask during NPPV can increase FIO2 and conserve oxygen. This study provides theoretical basis for the development of newer masks. Key words: Respiration, artificial; Tidal volume; Oxygen inhalation therapy; Intermittent positive-pressure breathing; Non-invasive ventilation