RT Journal Article SR Electronic T1 Impact of Humidification and Nebulization during Expiratory Limb Protection: An experimental bench study. JF Respiratory Care FD American Association for Respiratory Care SP respcare.01785 DO 10.4187/respcare.01785 A1 Alexandre Tonnelier A1 François Lellouche A1 Pierre Alexandre Bouchard A1 Erwan L'Her YR 2012 UL http://rc.rcjournal.com/content/early/2012/12/04/respcare.01785.abstract AB BACKGROUND: Different filtering devices are used during mechanical ventilation to avoid dysfunction of flow and pressure transducers or for airborne micro7organisms containment. Water condensates resulting from the use of humidifiers, but also residual nebulization particles, may have a major influence on expiratory limb resistances. OBJECTIVES: To evaluate the influence of nebulization and active humidification on the resistance of expiratory filters. METHODS: A respiratory system analog was constructed using a test lung, an ICU ventilator, heated humidifiers, and a piezoelectric nebulizer. Humidifiers were connected to different types of circuits (unheated, monoheated, biheated7new and old generation). Five filter types were evaluated (electrostatic, heat7and7moisture exchangers, standard, specific and internal heated HEPA). Differential pressure measurements were carried out after 247hrs of continuous in7vitro use for each condition, and after 24hrs of use with an old7generation biheated circuit without nebulization. Baseline characteristics were also obtained from each dry filter. RESULTS: While using unheated circuits, measures had to be interrupted before 247hrs for all filtering devices, except the internal heated HEPA. Heat7and7moisture exchangers occluded before H24 with unheated and mono7heated circuits. The circuit type, nebulization practice, or even the duration of use did not influence internal heated HEPA resistances. CONCLUSION: This bench7study confirms that expiratory limb filtration is likely to induce several major adverse events. Resistance of expiratory filters increase is mainly due to the humidification circuit type, rather than to nebulization itself. If filtration is mandatory while using unheated circuits, a dedicated filter should be used for equal or less than 247hrs, or a heated HEPA for a longer duration.