Comparison of the effects of heat and moisture exchangers and heated humidifiers on ventilation and gas exchange during non-invasive ventilation

Abstract

Objective: To compare the short-term effects of a heat and moisture exchanger (HME) and a heated humidifier (HH) during non-invasive ventilation (NIV). Design: Prospective, clinical investigation. Setting: Intensive care unit of a university hospital. Patients: Twenty-four patients with acute respiratory failure (ARF). Intervention: Each patient was studied with a HME and a HH in a random order during two consecutive 20min periods of NIV. Measurements and results: Respiratory rate (RR), expiratory tidal volume (VTe) and expiratory minute ventilation (VE) were measured during the last 5 min of each period and blood gases were measured. Mean pressure support and positive end-expiratory pressure levels were, respectively, 15±4 and 6±2 cmH2O. VE was significantly greater with HME than with HH (14.8±4.8 vs 13.2±4.3 l/min; p<0.001). This increase in VE was the result of a greater RR for HME than for HH (26.5±10.6 vs 24.1±9.8 breaths/min; p=0.002), whereas the VT for HME was similar to that for HH (674±156 vs 643±148 ml; p=0.09). Arterial partial pressure of carbon dioxide (PaCO2) was significantly higher with a HME than with a HH (43.4±8.9 vs 40.8±8.2 mmHg; p<0.005), without significantly changing oxygenation. Conclusion: During NIV the increased dead space of a HME can negatively affect ventilatory function and gas exchange. The effect of HME dead space may decrease efficiency of NIV in patients with ARF.