AN EVALUATION OF THE HEAT AND MOISTURE EXCHANGE PERFORMANCE OF 4 VENTILATOR CIRCUIT FILTERS

Objective: To compare the heat and moisture exchange efficiency of 4 commonly used ventilator circuit filters - DAR Hygroster (DHS), DAR Hygobac (DHC), Pall Ultipor BB50 (PUBC) and Intersurgical filtatherm (IFT). Design: Prospective randomized study. Setting: Intensive care unit of a university teaching hospital. Patients and Participants. 80 patients requiring post-operative mechanical ventilation were entered into the study. A total of 40 patients were studied after 1 h and 40 after 24 h. Due to technical errors 6 of the 1 h studies and 2 of the 24 h studies were excluded from analysis. Interventions: Mean wet and dry ceramic-platinum thermal probes were inserted in the inspiratory side of a divice which separated inspiratory and expiratory gas flows on the patient side of the ventilator circuit filter. Humidification efficiency was calculated with reference to these wet and dry bulb temperatures. Tracheal temperature was measured by a similar thermal probe in the tracheal tube. Measurements and results: Absolute humidity was greatest in group DHS (30.4 +/- 3.5 versus 22.9 +/- 1.5 mg/l at 1 h and 27.3 +/- 3.5 versus 20.7 +/- 2.4 mg/l at 24 h). The differences in absolute humidity reached statistical significance as follows: p = 0.0001 for DHS versus all others at 1 h and for DHS and DHC versus PUBC and IFT at 24 h. Conclusion: Better humidification capabilities were obtained with groups DHS and DHC than PUBC and IFT.