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' Bow 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.