Evaluating humidity recovery efficiency of currently available heat and moisture exchangers: a respiratory system model study.
OBJECTIVE
To evaluate and compare the efficiency of humidification in available heat and moisture exchanger models under conditions of varying tidal volume, respiratory rate, and flow rate.


BACKGROUND
Inspired gases are routinely preconditioned by heat and moisture exchangers to provide a heat and water content similar to that provided normally by the nose and upper airways. The absolute humidity of air retrieved from and returned to the ventilated patient is an important measurable outcome of the heat and moisture exchangers' humidifying performance.


METHODS
Eight different heat and moisture exchangers were studied using a respiratory system analog. The system included a heated chamber (acrylic glass, maintained at 37 degrees C), a preserved swine lung, a hygrometer, circuitry and a ventilator. Humidity and temperature levels were measured using eight distinct interposed heat and moisture exchangers given different tidal volumes, respiratory frequencies and flow-rate conditions. Recovery of absolute humidity (%RAH) was calculated for each setting.


RESULTS
Increasing tidal volumes led to a reduction in %RAH for all heat and moisture exchangers while no significant effect was demonstrated in the context of varying respiratory rate or inspiratory flow.


CONCLUSIONS
Our data indicate that heat and moisture exchangers are more efficient when used with low tidal volume ventilation. The roles of flow and respiratory rate were of lesser importance, suggesting that their adjustment has a less significant effect on the performance of heat and moisture exchangers.
Lucato
Jeanette Janaina Jaber
JJ
Pulmonary Division, Respiratory ICU, Hospital das Clinicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo, Brazil. jeanettejaber@yahoo.com
Adams
Alexander Bernard
AB
Souza
Rogério
R
Torquato
Jamili Anbar
JA
Carvalho
Carlos Roberto Ribeiro
CR
Marini
John J
JJ
D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D012121:Respiration, Artificial; D056152:Respiratory Rate / Q000502:physiology; D013990:Tidal Volume / Q000502:physiology; D012122:Ventilators, Mechanical