Comparison of manufacturers' specifications for 44 types of heat and moisture exchanging filters

Methods. Filter manufacturers were asked to provide technical information. Additional informationwasobtainedfromwebsites. Informationabout44filters(16mechanicaland28electrostatic) was collated. Results.Filter performances were estimated with different sizes of microorganism and durations of challenge. Twenty-eight filters had not been tested by independent laboratories. For 12 of the filters, information obtained from websites and from the manufacturers differed. Most filter specifications claimed high efficiency, particularly for filtration, microbial challenge number and test duration. Electrostatic filters used in anaesthesia were claimed to have high filtration efficiency, similar to the efficiency provided by mechanical filters. Excluding moisture output values did not alter the general conclusions. Conclusions. Technical aspects of the tests, international standards, and independent validation should be considered when a filter is chosen. Br J Anaesth 2004; 93: 532‐9