The humidification and heating (i.e., the conditioning) of medical gases is now a well-established clinical practice in intubated patients receiving invasive ventilatory support. The two most commonly used humidifying devices are the heated humidifier and the heat and moisture exchanger. At the present time, there is no information on the optimal level of the humidity of inspired gases during noninvasive ventilation (NIV). The American National Standard Institute suggested, although not directly for NIV, that 10 mgH2O/l of AH is the lowest acceptable level needed to minimize mucosal damage in the upper airways. The NIV can be delivered by a facial mask or by a helmet. Differently from the face mask, the higher internal volume of the helmet (12–15 l vs. 0.3 l) generates a mixing chamber between the expired and inspired medical gases, thus increasing the level of temperature and humidity. By delivering CPAP (continuous positive airway pressure) with a common ventilator by helmet, the level of humidity was higher than the minimum required level. On the contrary, by applying CPAP with continuous CPAP flow, it seems reasonable to use a heated humidifier. When using a face mask, a heated humidifier or heat moisture exchanger should always be used.
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