The effect of inlet gas temperatures on heated humidifier performance

The aim of the current study was to determine the temperature range of gas at the point at which it passes into a heated humidifier within an intensive care unit and to experimentally examine the effect of different inlet gas temperatures on the performance of a heated humidifier. Various gas and ambient temperatures were measured in an intensive care unit and within ventilator circuits. Ventilator oxygen and air inlet temperatures, ventilator gas outlet temperatures, and humidifier gas inlet temperatures were measured in conjunction with the use of a number of ventilators. Ambient temperatures within the ward ranged from 22.8 degrees C to 28.9 degrees C, while typical ward humidifier gas inlet temperatures ranged from 24.3 degrees C to 28.8 degrees C. Humidity output from a heated humidifier was then determined in an experimental setup at controlled levels of inlet gas temperature using a constant gas flow. A decrease in humidity production, from approximately 36 mg/L at a humidifier inlet gas temperature of 18 degrees C, to 26 mg/L at a humidifier inlet gas temperature of 32 degrees C, was observed with increasing gas inlet temperature. We conclude that humidity output from a heated humidifier varies with inlet gas temperature, decreasing as inlet gas temperature increases. Inlet gas temperatures above 26 degrees C may result in inadequate humidification.