A comparative evaluation of disposable humidifiers.

The performance of four hygroscopic condenser humidifiers (HCH) and two conventional heat and moisture exchangers (HME), all commercially available, have been evaluated in laboratory tests. A clinical study was also made in order to confirm the test results. It was found that the new generation of heat and moisture exchangers, which have hygroscopic properties, are superior to conventional HME units. When dry inspired gases are used, the HCH units, but not the HME units, deliver a moisture level that is comparable to what is produced in the upper trachea during normal breathing the nose. Our clinical experience as well as the extensive body of literature on humidification requirements support the conclusion that in most cases they can be recommended to be used for extended time periods even with dry gases. The humidification efficiency decreases with increasing tidal volume for all units. However, the best units can be used up to tidal volumes of 1000-1500 ml. The dead space of these units varies from 90 ml to 100 ml and the resistances are only about 50 Pa at 0.5 l/s. The weight is in the range 18-40 g. One of the best HCH devices also has distinct antimicrobial properties. The others are found at least not to promote organism growth. This feature added to others such as safety and simplicity in use make an HCH device an attractive alternative to conventional humidification techniques.