Effect of Inspiratory Absolute Humidity on Leak During NPPV

Abstract

Noninvasive ventilator connects a one-way circuit with leak and delivers inspired gas via the upper airway tract. A heated humidifier don't have to connect to contain heat and moisture exchange humidity in the upper airway functions. However, there are many case connecting a heated humidifier to be inadequate humidity in the upper airway. The purpose of this study was to clarify the influence of absolute humidity on leak and inspiratory positive airway pressure during noninvasive positive pressure ventilation. We connected respiratory machine, a heated humidifier and a model lung via two type circuits. One circuit was a single-limb breathing with an exhalation port and another was two-way circuits to distinguish the inspiratory from the expiratory via Y-piece. Two heated humidifiers were included in both inspiratory and expiratory circuits to simulate the physical lung. Relative humidity, temperature and flow rate were measured for 30 minutes. Absolute humidity was calculated using the Teten's equation and a gas state equation with relative humidity and temperature. In results, flow rate increased and absolute humidity decreased, when leak volume increased. We presumed that warmer humidified gas was discharged through the leak port with increasing flow rate to compensate leak. However, absolute humidity slightly was not associated with higher inspiratory positive airway pressure at the steady leak. We supposed that expiratory gas was not capable to discharge due to increasing flow rate and might be accumulated into the mask. The expired gas temperature accumulated in the mask might affect the inspired absolute humidity. Consequently, we are desirable to measure the inspired gas temperature and absolute humidity. In conclusion, absolute humidity would depend on leak during noninvasive positive pressure ventilation.