[Water permeability of breathing filters]

Breathing filters or heat and moisture exchangers (HME), which are placed between a tracheal tube and the Y-piece, allow reuse of breathing tubes without changing between operations. During low-flow and minimal-flow anaesthesia, condensed water accumulates in the breathing circuit. An evaluation of the volume of condensed water is given (Fig. 1). It may be possible that water flows onto the filter surface, for example, when the breathing tubes are lifted. The water permeability of such breathing filters and HME was tested. For the experiments, a commercial breathing circuit and ventilator (Dräger Sulla 808 + Ventilog) and patient model (Fig. 2) were used; 12 breathing filters/HMEs of different manufacturers were tested. Only 3 filters were not permeable to the test volume of 20 ml water. The authors suggest the water volume be checked routinely and the breathing tubes be emptied if necessary.