Performance Characteristics of Conventional and Prototype Humidifiers and Nebulizers

¹ Departments of Anesthesiology and Chemical Engineering, the University of Florida, Gainesville

The output of water from conventional and experimental humidification devices was determined under conditions similar to those encountered by a patient who is intubated and spontaneously breathing. Absolute humidity was measured by a modified dewpoint hygrometer, and relative humidity at 37°C was then calculated. Only two of the unheated pneumatic nebulizers tested were capable of delivering near 100 percent relative humidity at 37°C, while both ultrasonic nebulizers tested were able (at maximum outputs) to more than double this humudity content. An external heat source was necessary to increase the water content of gases delivered from pure humidifiers (no particulate water output) to above 50 percent relative humidity at 37°C. No correlation could be made between visible fog and actual water content in the humidified gases. Frequent changes in control were necessary to maintain a constant output when the heated humidifier was run continuously for a six-hour period, while prolonged warm-up periods were necessary prior to achieving stable outputs when the ultrasonics were so tested. The most efficient unheated pneumatics, however, maintained a stable and satisfactory output throughout the six-hour test period. It was concluded that the newer pneumatically driven, unheated nebulizers are capable of delivering gases with nearly 100 percent relative humidity at 37°C, therefore eliminating the need for heated or ultrasonically driven nebulizers for routine clinical use.