A comparison of two heated water-bath humidifiers.

The performance of two heated water-bath humidifiers was examined in terms of airway temperatures and humidities. These were the simple heated tank (Marshall and Spalding, 1953) and the Fisher and Paykel No. 328 (Spence and Melville, 1972), both of which had the potential to deliver gases at temperatures above 40 degrees C, and with a moisture content in excess of 50 mg/litre. The major advantage of the No. 328 was its heating wire in the delivery tube. This lessened or prevented condensation within the tube, and allowed the water bath to be maintained at lower temperatures. Independent heat controls for the water bath and the delivery tubing allow precision of humidities in the gases provided for inspiration through an artificial airway. When condensation is prevented, the temperature of the saturated gases leaving the humidifier limits the absolute humidity supplied. Monitoring and adjustment of airway temperature of the patient then allows selection of temperature and relative humidity in the inspired gas.