Correlation between simple clinical parameters and the in vitro humidification characteristics of filter heat and moisture exchangers

Study objective: This study on ventilated patients in ICUs examined a large sample of heat and moisture exchanger filters (HMEFs) to determine whether simple clinical parameters are correlated with exchanger humidity output. Design: A total of 594 HMEFs (18 types of HMEF) were tested in nine university hospital ICUs, Patients: Each HMEF was tested on one different unselected and consecutive patient for 24 h. Interventions: The following parameters were rated at each tracheal aspiration on a scale of 0 to 3: secretion abundance, viscosity (Visc), suction catheter adherence (Adh) to the endotracheal tube, and the amount of water condensed in the flex tube (Cond), Individual values for each type of HMEF and each variable were averaged and correlated with the humidity output (HO) of the HMEFs, values which were supplied by the manufacturers, Results: There were significant correlations between HO and Cond (r=0.82, p<10(-3)), Vise (r=-0.67, p=0.002), and Adh (r=-0.56, p=0.01). A second study recorded the same variables, for three consecutive 24-h periods, using first a high-humidifying HMEF (DAR Hygrobac), followed by a lo cv-humidifying one (Pall BB22-15), and again DAR Hygrobac. Vise and Adh were higher (p<0.05) and Cond was lower (p<0.05) with the Pall than with the DAR. Conclusions: Simple clinical parameters correlate well with the efficiency of HMEFs. The apparent water condensed in the flex tubing seems to be the best indicator of the humidifying efficiency of HMEFs.