Study objective: To evaluate in patients submitted to minute ventilation > 10 L/min the ability to preserve patients' heat and humidity of two heat and moisture exchangers (HMEs) and one vaporizing humidifier (VH).
Design: Prospective, randomized, comparative, non-blinded study.
Setting: Intensive care unit of a university hospital.
Patients: Nine tracheally intubated, mechanically ventilated patients, sedated and submitted to mechanical ventilation with minute ventilation > 10 L/min.
Interventions: Using the psychrometric method, relative humidity (RH) and absolute humidity (AH) of inspired gas were obtained as well as temperature of inspired gas and tracheal temperatures (maximal and minimal). Following a randomized order, each patient was ventilated for two 24-h periods with a vaporizing humidifier (Bennett Cascade 2, Bennett; France) and one of two HMEs: Pall Ultipor filter BB50 (Pall Biomedical; France) or DAR Hygroster filter (Peters; France). Both were first tested for a 45-min period and then the HME that achieved the best performance in terms of temperature and water preservation was tested for 24 h.
Measurements and results: During the 45-min test period, the Pall Ultipor HME achieved a lower performance than the other two systems for any of the studied parameters (p < 0.05 to p < 0.0001). The DAR Hygroster HME achieved lower temperature of inspired gas (29.9 vs 32.0 degrees C, p < 0.005) and lower absolute humidity (29.3 vs 33.2 mg H2O/L, p < 0.005) than the Bennett Cascade 2. After 24 h of use, lower values of temperature of inspired gas (28.5 vs 32.0 degrees C, p < 0.002) and of AH (28.0 vs 33.6 mg H2O/L, p < 0.001) were obtained with the DAR Hygroster HME than with the Bennett Cascade 2. No differences were found between the two systems for the other tested parameters. At that time, no patients had RH lower than 97% and absolute humidity lower than 23 mg H2O/L with the use of the DAR Hygroster HME.
Conclusions: In patients with minute ventilation > 10 L/min, the DAR Hygroster HME showed a thermic and humidification capability similar to the reference system, the Bennett Cascade 2 VH. In these patients, the Pall Ultipor HME had a significantly lower capability.