"In vitro" evaluation of Heat and Moisture Exchangers designed for spontaneous breathing tracheostomized patients.

Background: Heat and moisture exchangers (HMEs) are commonly used in chronically tracheostomized spontaneously breathing patients to condition inhaled air maintaining lower airway functions and minimizing viscosity of secretions. Supplemental oxygen flow can be added to most HMEs designed for spontaneously breathing tracheostomized patients. Aim of the Study: To test the efficiency of seven HMEs designed for spontaneously breathing tracheostomized patients in a normothermic model at different minute ventilations (Ve) and supplemental oxygen flows. Methods: HME efficiency was evaluated using an in vitro lung model at two V (5 and 15 L/min) and four supplemental O2 flows (0, 3, 6, and 12 L/min). Wet and dry temperature of the inspiratory flow was 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 O2 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 Ve . The HME with the best performance resulted in an absolute humidity of 26 mgH O2/L and a temperature of 27.8°C. No significant changes in efficiency or resistance were detected during the 24 h evaluation. Conclusions: The efficiency of HMEs in terms of temperature output and absolute humidity is significantly affected by O2 supplementation and Ve.

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 (O2) 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 (VE) and supplemental O2 flows. Methods: HME efficiency was evaluated using an in vitro lung model at 2 VE (5 and 15 L/min) and 4 supplemental O2 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 O2 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 VE. The HME with the best performance provided an absolute humidity of 26 mg H2O/L and a temperature of 27.8°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 O2 supplementation and VE. © 2013 Daedalus Enterprises.