The moisture-conserving performance of breathing system filters during the first three minutes of simulated use.

Abstract

Breathing system filters are recommended for use during anaesthesia to protect the patient from inhaling gas-borne particles. Filters placed at the patient connection port of the breathing system can also humidify the inspired gases. The end-inspired moisture content was measured when using five different filters with two different ventilatory test conditions on a patient model during a typical pre-oxygenation period of 3 min. The moisture content of the end-inspired air at the end of the 3-min period varied from 6.4 to 27.8 and from 4.4 to 25.9 g.m-3 for tidal volumes of 0.5 and 1.0 l, respectively (p < 0.0001 for all pairwise comparisons of the five filters and for the two tidal volumes). Those breathing system filters that have at least an adequate level of performance (at least 20 g.m-3) will generally achieve this level within the 3-min pre-oxygenation period.