Comparison of Conventional Heated Humidification with A New Active Hygroscopic Heat and Moisture Exchanger in Mechanically Ventilated Patients

Abstract

Background

Humidification has traditionally been supplied by heated humidifiers and, more recently, passive humidifiers. We compared a new active heat and moisture exchanger (AHME) to traditional heated humidification (HH) and heated humidification with a heated wire circuit (HH+HWC). DEVICE STUDIED: The AHME (Humid Heat, Louis Gibeck AB, Sweden) uses a hygroscopic heat and moisture exchanger (HHME) combined with a heat and water source. The HHME is modified to include a cone-shaped housing between the media and the patient. A control unit pumps water to a wick inside the housing, based on the set value for the patient's minute volume. The cone-shaped HHME is inserted into an exterior heater, which only heats the area around the wick. The system is designed to provide an air temperature of 37° C. A temperature probe monitors airway temperature.

Methods

Following informed consent from the next of kin, 30 patients requiring mechanical ventilation for > 72 hours were studied. Patients were ventilated using HH, HH+HWC, and AHME in random order for 24 hours each. All devices were set to deliver gas at 37° C at the proximal airway. Daily measurements were made of minimum and maximum body temperatures, number of suctioning procedures, volume and quality of secretions, volume of instilled saline, number of times condensate was drained from the circuit, water usage, and circuit disconnections. Resistance of the HHME portion of the AHME was measured before and after use. Measurements of relative humidity and temperature at the endotracheal tube were made daily.

Results

There were no differences related to the indices of adequate humidification (secretion volume and consistency, number of suctioning attempts, or volume of saline used). All devices provided similar measured airway temperatures and humidity. There were also no differences in the daily minute volume or bias flow for flow-triggering. There were significant differences between devices in water usage per 24 hours (HH = 2039 ± 387 mL, HH+HWC = 766 ± 281 mL, AHME = 135 mL ± 53 mL, p < 0.001). The volume of condensate was also significantly less for the HH+HWC and AHME, compared to HH (HH = 930 ± 271 mL, HH+HWC = 12 ± 6, and AHME = 1 ± 3 mL, p < 0.001). AHME resistance was relatively unchanged from start to finish (1.7 ± 0.1 cm H2O/L/s vs 2.3 ± 0.8 cm H2O/L/s).

Conclusions

In this preliminary study, the new AHME provided similar humidification to traditional HH and HH+HWC, but with significantly lower water usage and less condensate than HH or HH+HWC. Disadvantages of the AHME system include added dead space (73 mL) and more weight on the endotracheal tube. However, if a flex tube is used in the HH system, only 54 mL of dead space is added.