Short-Term Effects of an Active Heat-and-Moisture Exchanger During Invasive Ventilation

BACKGROUND: Humidification is a standard of care during invasive mechanical ventilation. Two types of devices are used for this purpose: heated humidifiers and heat-and-moisture exchangers (HME).

AIM: To compare the short-term physiologic effects of an active HME, with those of heated humidifiers and HMEs in terms of respiratory effort, ventilatory pattern, and arterial blood gases during invasive mechanical ventilation.

METHODS: We conducted a randomized crossover study with 3 different devices in 15 stable subjects who had a tracheostomy and were ventilator-dependent. Transdiaphragmatic pressure, ventilatory pattern, arterial blood gases, and dyspnea scale were recorded at baseline and at the end of a 20-min period with each device.

RESULTS: Compared with heated humidifiers, the active HME was associated with higher diaphragmatic pressure-time product per minute (117.10 [interquartile range {IQR} 34.58–298.60]) versus 80.86 (IQR, 25.46–110.55) cm H₂O×s/min, P = .01), higher P_aCO2 (48.50 [IQR, 40.65–53.70] vs 39.60 [IQR, 37.50–49.95]) mm Hg, P = .02) and lower pH (7.41 [IQR, 7.36–7.49] vs 7.45 [IQR, 7.40–7.51], P = .030) without any significant difference in ventilatory pattern. A significantly worse dyspnea scale score (active HME, 3 (2–4) vs heated humidifiers: 4 (3–5); P = .009) was also observed. No significant differences were seen between active HME and HME.

CONCLUSIONS: This study indicated that, compared with the heated humidifiers, the use of the active HME or the HME increased inspiratory effort, P_aCO2, pH, and dyspnea in stable subjects who were tracheostomized and ventilator-dependent.