Which of the following is true concerning heat and moisture exchangers?

a. They are passover type A humidifiers.
b. They might reduce the incidence of noso-comial infections.
c. They are best-suited for long-term use on mechanical ventilators.
d. They are able to provide a humidity output of 10 mg/L to 44 mg/L at 35? C.

ANS: B
Heat and moisture exchangers might reduce the incidence of nosocomial infections. Passive hu-midifier heat and moisture exchangers have been successfully used to meet the short-term hu-midification needs of spontaneously breathing and mechanically ventilated patients with endo-tracheal and tracheostomy tubes. However, a heat and moisture exchanger is not a passover hu-midifier. The passover humidifier directs gas over a liquid or liquid-saturated surface. Heat and moisture exchanging filters have an increased internal surface area and are capable of providing moisture output in the range of 18 mg H2O/L to 28 mg H2O/L. According to the American Asso-ciation for Respiratory Care's Clinical Practice Guideline, heat and moisture exchangers should not be used for long-term humidification of patients who are receiving invasive mechanical ven-tilation.