In vitro evaluation of an active heat-and-moisture exchanger: the Hygrovent Gold.

BACKGROUND To improve the heat and humidification that can be achieved with a heat-and-moisture exchanger (HME), a hybrid active (ie, adds heat and water) HME, the Hygrovent Gold, was developed. We evaluated in vitro the performance of the Hygrovent Gold. METHODS We tested the Hygrovent Gold (with and without its supplemental heat and moisture options activated), the Hygrobac, and the Hygrovent S. We measured the absolute humidity, using a test lung ventilated at minute volumes of 5, 10, and 15 L/min, in normothermic (expired temperature 34 degrees C) and hypothermic (expired temperature 28 degrees C) conditions. We also measured the HMEs' flow resistance and weight after 24 h and 48 h. RESULTS In its active mode the Hygrovent Gold provided the highest absolute humidity, independent of minute volume, in both normothermia and hypothermia. The respective normothermia and hypothermia absolute humidity values at 10 L/min were 36.3 + 1.3 mg/L and 27.1 + 1.0 mg/L with the active Hygrovent Gold, 33.9 + 0.5 mg/L and 24.2 + 0.8 mg/L with the passive Hygrovent Gold, 33.8 + 0.56 mg/L and 24.4 + 0.4 mg/L with the Hygrobac, and 33.9 + 0.8 mg/L and 24.6 + 0.6 mg/L with the Hygrovent S. The efficiency of the tested HMEs did not change over time. At 24 h and 48 h the increase in weight and flow resistance was highest in the active Hygrovent Gold. CONCLUSIONS The passive Hygrovent Gold provided adequate heat and moisture in normothermia, but the active Hygrovent Gold provided the highest humidity, in both normothermia and hypothermia.