Abstract
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.
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