title: In vitro evaluation of heat and moisture exchangers designed for spontaneously breathing tracheostomized patients.
abstract: 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 V(E).
authors.affiliation: Dipartimento di Scienze Chirurgiche e Diagnostiche Integrate, Sezione Anestesia e Rianimazione.
authors.forename: Claudia
authors.initials: C
authors.lastname: Brusasco
authors.forename: Francesco
authors.initials: F
authors.lastname: Corradi
authors.forename: Maria
authors.initials: M
authors.lastname: Vargas
authors.forename: Margherita
authors.initials: M
authors.lastname: Bona
authors.forename: Federica
authors.initials: F
authors.lastname: Bruno
authors.forename: Maria
authors.initials: M
authors.lastname: Marsili
authors.forename: Francesca
authors.initials: F
authors.lastname: Simonassi
authors.forename: Gregorio
authors.initials: G
authors.lastname: Santori
authors.forename: Paolo
authors.initials: P
authors.lastname: Severgnini
authors.forename: Robert M
authors.initials: RM
authors.lastname: Kacmarek
authors.forename: Paolo
authors.initials: P
authors.lastname: Pelosi
mesh_terms: D004867:Equipment Design; D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D008168:Lung / Q000503:physiopathology; D008962:Models, Theoretical; D015203:Reproducibility of Results; D012119:Respiration; D012121:Respiration, Artificial / Q000295:instrumentation*; D012131:Respiratory Insufficiency / Q000503:physiopathology / Q000628:therapy*; D014139:Tracheostomy; D015300:Ventilator Weaning / Q000295:instrumentation*; D012122:Ventilators, Mechanical / Q000592:standards*
keywords: absolute humidity; air conditioning; heat and moisture exchangers; inspiratory air temperature; tracheostomized patients