Performance of heated wire humidifiers: An in vitro study

PURPOSE: We assessed the performance of heated wire humidifiers (HWHs), which should avoid water condensation in the circuit. METHODS: We evaluated the efficiency of 3 HWHs, MR850 (Fisher & Paykel, Auckland, New Zealand), CONCHATHERM IV (Hudson RCI, Temecula, Calif), and DAR HC 2000 (Mallinckrodt DAR, Mirandola, Italy), in comparison with that of the MR730 heated humidifier (HH), which has a standard circuit. We measured gas temperature and absolute humidity (AH) at the Y piece of the ventilatory circuit using a test lung ventilated at 2 minute ventilation volumes (5 and 15 L/min). Temperature levels at the Y piece of the ventilatory circuit of the HHs were set at 35 degrees C, 37 degrees C, and 39 degrees C with different gradients (-2 degrees C, 0 degrees C, and +2 degrees C) between the outlet chamber and the Y piece of the ventilatory circuit. RESULTS: At the set temperature levels of 35 degrees C, 37 degrees C, and 39 degrees C with a gradient of 0 degrees C, the MR850 and CONCHATHERM IV had lower gas temperature and AH levels as compared with the DAR HC 2000 and MR730 HH. With increasing temperature gradient, gas temperature increased only with the CONCHATHERM IV but AH increased with all the HWHs. The MR850 showed lower gas temperature and AH levels as compared with CONCHATHERM IV. The condensate was abolished inside the inspiratory circuit with the HWHs. CONCLUSIONS: Heated wire humidifiers eliminate water condensation but present significant differences in gas temperature and AH levels that are lower than the expected settings.