Humidification in the upper respiratory tract: a physiological overview.

Over the last 30 years, there has been a wealth of literature investigating the principles of humidification in the upper respiratory tract. Most of the nursing literature provides subjective information, whilst the medical profession presents concrete objective data based on sound clinical research. A great deal of information does not date; the physiological principles of humidification remain unchanged. As a clinical nurse adviser with previous experience of humidification trials (Jackson & Webb 1992), I was invited by the Trust Clinical Practice Group, which is responsible for practice development issues, to design humidification guidelines for use in the Trust. Such work is necessarily based on sound knowledge of normal physiology and hazards of artificial humidification. This article contains an outline of the concept of humidity, examination of the normal mechanism of humidification, and details of consequences of over- and under-humidification. Finally, the concept of optimal humidification is discussed, and the main mechanisms of viral and bacterial contamination of the upper airways are briefly detailed.