In Vitro Evaluation of Heat and Moisture Exchangers Designed for Spontaneously Breathing Tracheostomized Patients

BACKGROUND: Heat and moisture exchangers (HMEs) are commonly used in chronically tracheostomized spontaneously breathing patients, to condition inhaled air, maintain lower airway function, and minimize the viscosity of secretions. Supplemental oxygen (O-2) can be added to most HMEs designed for spontaneously breathing tracheostomized patients. We tested the efficiency of 7 HMEs designed for spontaneously breathing tracheostomized patients, in a normothermic model, at different minute ventilations ((V) over dot(E)) and supplemental O-2 flows. METHODS: HME efficiency was evaluated using an in vitro lung model at 2 (V) over dot(E) (5 and 15 L/min) and 4 supplemental O-2 flows (0, 3, 6, and 12 L/min). Wet and dry temperatures of the inspiratory flow were measured, and absolute humidity was calculated. In addition, HME efficiency at 0, 12, and 24 h use was evaluated, as well as resistance to flow at 0 and 24 h. RESULTS: The progressive increase in O-2 flow from 0 to 12 L/min was associated with a reduction in temperature and absolute humidity. Under the same conditions, this effect was greater at lower (V) over dot(E). The HME with the best performance provided an absolute humidity of 26 mg H2O/L and a temperature of 27.8 degrees C. No significant changes in efficiency or resistance were detected during the 24 h evaluation. CONCLUSIONS: The efficiency of HMEs in terms of temperature and absolute humidity is significantly affected by O-2 supplementation and (V) over dot(E). (C) 2013 Daedalus Enterprises