Heat and moisture exchangers with bacterial filters: a laboratory evaluation.

Six commercially available heat-moisture exchanger (HME) humidifiers with built-in bacterial filtration were evaluated by laboratory tests. Physical characteristics, humidification efficiency, resistance to flow and filtration capability were investigated. The resistance was comparable for all units and did not change notably with exposure to humidity. Deadspace values were in the range 55-92 ml and weight values between 34-55 g. The humidification efficiency of two units (Group 1) was clearly less (54%-63% at 11 tidal volume), than for the other four devices (Group 2) (77%-82%). This corresponds to an average humidification output of 22.0 g/m3 for Group 1 as compared to an output of 29.9 g/m3 for Group 2. The average filtration capability of Group 1 was 99.9998%, which is somewhat higher than the 99.9973% obtained for Group 2. There are significant differences between the humidification efficiency and deadspace of different units, with the Pall Conserve device having the least satisfactory performance. All units exhibit good filtering properties, with the Pall Conserve device performing best in this respect.