ABSTRACT
The administration of gases in non-invasive ventilation (NIV) requires adequate levels of humidification and heating. Humidity may be expressed in terms of absolute humidity (AH, mg H2O/L) or relative humidity (RH, per cent). Humidity or hygrometric levels may extend over a wide range, thus giving rise to diverse consequences, all of which may be controlled by increasing the level of AH in the gas delivered to NIV.1,2
In acute NIV, a high respiratory rate causes the loss of internal AH. Mouth closure should prevent a decrease in AH.3,4 Mouth or peripheral mask leak produces a constant loss in AH which, when combined with an inadequate AH level, may cause a wide variety of potential problems, as has been described for acute or chronic NIV applications. The main effects are summarized in Box 8.1.
