Objective: The purpose of this study was to assess and compare the humidification, heating, and resistance properties of three commercially available heat-moisture exchangers (HMEs). To mimic clinical conditions, a previously validated, new, realistic experimental set-up and measurement protocol was used.
Design: Prospective, comparative experimental study.
Setting: Surgical Intensive Care Unit, University Hospital of Rotterdam.
Materials: An experimental set-up consisting of a patient model, measurement systems, and ventilator and three different HME types.
Interventions: The air flow, pressure in the ventilation circuit, pressure difference over the HME, and partial water vapour pressure and temperature at each side of the HMEs were measured. Measurements were repeated every 30 min during the first 2 h and every hour up to 24 h for each HME at six different ventilator settings. The mean inspiratory and maximum expiratory resistance, flow-weighted mean absolute humidity and temperature outputs, and humidification and heating efficiencies of HMEs were calculated.
Measurements and results: The Dar Hygroster had the highest humidity output, temperature output, humidification efficiency, and heating efficiency values throughout the study (32.8 +/- 21. mg/l, 32.2 +/- 0.8 degrees C, 86.3 +/- 2.3%, and 0.9 +/- 0.01%, respectively) in comparison to the Humid-Vent Filter (25.3 +/- 3.2 mg/l, 31.9 +/- 0.8 degrees C, 72.2 +/- 5.3%, 0.9 +/- 0.02%, respectively) and the Pall Ultipor BB100 breathing circuit filter (23.4 +/- 3 mg/l, 28.3 +/- 0.7 degrees C, 68.8 +/- 5.9%, 0.8 +/- 0.02%, respectively). The inspiratory and expiratory resistance of the HMEs remained below clinically acceptable maximum values (2.60 +/- 0.04 and 2.45 +/- 0.05 cmH2O/l per s, respectively).
Conclusion: The Dar Hygroster filter was found to have the highest humidity and temperature output of all three HMEs, the Humid-Vent filter had a satisfactory humidity output only at low tidal volume flow rate and minute volume settings, whereas the Pall Ultipore BB 100 never achieved a sufficient humidity and temperature output.