Air flow resistance of three heat and moisture exchanging filter designs under wet conditions: implications for patient safety †

Abstract

Heat and moisture exchanging filters (HMEFs) can be blocked by secretions. We have studied HMEF performance under wet conditions to see which particular design features predispose to this complication. Dar Hygrobac-S (composite felt filter and cellulose exchanger), Dar Hygroster (composite pleated ceramic membrane and cellulose exchanger) and Pall BB22-15 (pleated ceramic membrane) HMEFs were tested. Saline retention, saline concealment, and changes in air flow resistance when wet were assessed. The cellulose exchanger in the composite Hygrobac-S and Hygroster retained saline, producing a 'tampon' effect, associated with bi-directional air flow resistances in excess of the international standard of a 5 cm H(2)O pressure drop at 60 litre min(-1) air flow. Furthermore, high air flow resistances occurred before free saline was apparent within the transparent filter housing. The pleat only BB22-15 showed a significant increase in expiratory air flow resistance, but only after the presence of saline was apparent. These data imply that composite HMEFs with cellulose exchangers are more likely to block or cause excessive work of breathing as a result of occult accumulation of patient secretions than pleat only HMEFs.

Temperature and humidity of the Dr�ger Cato anesthetic machine circuit

“…To address this concern, apparatuses such as heat moisture exchangers (HME) are used to humidify anesthetic circuits in clinical situations [1,6]. Some anesthetic machines inherently humidify and warm anesthetic gases.…”

Tidal Volume Delivery From ICU Ventilators at BTPS Conditions: A Bench Study

“…High Rf value has been also reported for Hygrobac S by others. 12 Lellouche et al 13 found that the pressure drop measured at 1 L/s was 2 cm H 2 O for Hygrobac and 1.9 cm H 2 O for Sterivent after a 3-hour exposure to a wet environment. This latter value was lower than that presently found, a discrepancy that can be explained by difference in time frame.…”

Ventilatory changes during the use of heat and moisture exchangers in patients submitted to mechanical ventilation with support pressure and adjustments in ventilation parameters to compensate for these possible changes: a self-controlled intervention study in humans

“…(22,30,31,34,48,49) This increase in resistance in the ventilatory circuit may lead to an incorrect evaluation of respiratory system mechanics, inappropriate treatment (bronchodilators) or difficulty in mechanical ventilation weaning, (31) in addition to increasing the patient's breathing effort. (18,31,50) …”