RT Journal Article SR Electronic T1 Influence of ambient temperature and minute ventilation on passive and active heat and moisture exchangers JF Respiratory Care FD American Association for Respiratory Care SP respcare.02523 DO 10.4187/respcare.02523 A1 François Lellouche A1 Siham Qader A1 Solenne Taillé A1 Aissam Lyazidi A1 Laurent Brochard YR 2013 UL http://rc.rcjournal.com/content/early/2013/10/08/respcare.02523.abstract AB Background: During invasive mechanical ventilation, inspired gases must be humidified. We previously showed that high ambient temperature greatly impaired hygrometric performances of heated wire heated humidifiers. The aim of this bench and clinical study was to assess the humidification performances of passive and active heat and moisture exchangers (HME) and the impact of ambient temperature and ventilator settings. Methods: We first tested on bench a device with passive and active humidification properties (Humid-Heat, Hudson), and two passive hydrophobic/hygroscopic HMEs (Hygrobac and Hygrobac-S, Mallinkrodt). The devices were tested at three different ambient temperature (from 22 to 30°C), and at two minute ventilations (10 and 20L/min). Inspired gas hygrometry was measured at Y-piece with the psychrometric method. In addition to the bench study, we measured hygrometry of inspired gases in two different clinical studies. In 15 mechanically ventilated patients, we evaluated Humid-Heat at different settings. Additionnaly, we evaluated Humid-Heat and compared it with Hygrobac in a cross-over study in 10 patients. Results: On bench, with the Hygrobac and Hygrobac S, inspired absolute humidity was around 30 mgH2O/L and with the Humid-Heat, slightly below 35 mgH2O/L. Ambient temperature and minute ventilation did not have a clinically significant difference on the performances of the tested devices. During the clinical evaluation, Humid-Heat provided inspired humidity in a range from 28.5 mgH2O/L to 42.0 mgH2O/L, depending on settings, and was only weakly influenced by patient's body temperature. Conclusion: in this study, both passive and active HME had stable humidification performances with negligible influence of ambient temperature and minute ventilation. This contrasts with previous findings with heated wire heated humidifiers. Although there is no clear data demonstrating that higher humidification impact outcomes, it is worth noting that humidity was significantly higher with the active HME.