We combined a bacteria-filtering heat-moisture exchanger (HMEF), the Pall Conserve (PC), with an unheated Cascade humidifier (UH) to provide the additional humidity necessary to avoid thickening sputum in the long-term mechanically ventilated patient. METHODS AND MATERIALS: We measured the relative humidity and calculated the absolute humidity in the inspired tidal volumes of a healthy, adult patient, with the PC combined and not combined with a UH. Resistance to airflow through the PC was measured continuously for 48 h under two conditions (with and without the UH) and in two positions (upright and horizontal). Clinical testing consisted of ventilating 19 subjects for up to 13 days with the PC-UH combination as the humidifying device. RESULTS: Calculated absolute humidity rose significantly with the PC-UH combination at 5, 15, and 30 min of use. Resistance rose slightly over time, with the greatest increase occurring after 24 h in the horizontally positioned PC combined with the UH. Sputum viscosity changed very little, and in no case was it deemed necessary to provide humidification by heated humidifier. CONCLUSION: We believe that combining the Pall Conserve with an unheated humidifier preserves the advantages of the HMEF and provides the additional humidity required to avoid thickening sputum.
Suzukawa et al. (Wed,) studied this question.