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 aheat-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 theHygrovent Gold. METHODS: We tested the Hygrovent Gold (with and without its supplemental heat andmoisture options activated),the Hygrobac,and the Hygrovent S. We measured theabsolute humidity,using a test lung ventilated at minute volumes of 5,10,and15 L/min,in normothermic (expired temperature 34 degrees C) and hypothermic(expired temperature 28 degrees C) conditions. We also measured the HMEs' flowresistance and weight after 24 h and 48 h. RESULTS: In its active mode the Hygrovent Gold provided the highest absolutehumidity,independent of minute volume,in both normothermia and hypothermia. Therespective normothermia and hypothermia absolute humidity values at 10 L/min were36.3 + 1.3 mg/L and 27.1 + 1.0 mg/L with the active Hygrovent Gold,33.9 + 0.5mg/L and 24.2 + 0.8 mg/L with the passive Hygrovent Gold,33.8 + 0.56 mg/L and24.4 + 0.4 mg/L with the Hygrobac,and 33.9 + 0.8 mg/L and 24.6 + 0.6 mg/L withthe Hygrovent S. The efficiency of the tested HMEs did not change over time. At24 h and 48 h the increase in weight and flow resistance was highest in theactive Hygrovent Gold. CONCLUSIONS: The passive Hygrovent Gold provided adequate heat and moisture innormothermia,but the active Hygrovent Gold provided the highest humidity,inboth normothermia and hypothermia.