Laboratory Evaluation of 10 Heat and Moisture Exchangers Using Simulated Aeromedical Evacuation Conditions

Abstract

Heat and moisture exchangers (HMEs) are used for airway humidification in mechanically ventilated patients and have been evaluated only under hospital conditions. U.S. Air Force aeromedical evacuation transports are performed under rugged conditions further complicated by the cold and dry environment in military aircrafts, and HMEs are used to provide airway humidification for patients. This study evaluated 10 commercial HMEs using a test system that simulated aeromedical evacuation conditions. Although the American National Standards Institute recommends inspired air to be at an absolute humidity value of > or = 30 mg/L for mechanically ventilated patients, the highest absolute humidity by any HME was approximately 20 mg/L. Although none of the HMEs were able to maintain a temperature high enough to achieve the humidity standard of the American National Standards Institute, the clinical significance of this standard may be less important than the relative humidity maintained in the respired air, especially on evacuation flights of short duration.

Humidification on Ventilated Patients: Heated Humidifications or Heat and Moisture Exchangers?

“…The American National Standards Institute (ANSI) and the American Association for Respiratory Care (AARC) recommend an AH ≥30 mg H2O/L for the inspired air during mechanical ventilation [ 16 , 33 ], while the ISO (International Organization for Standardization) prefer AH values ≥ 33 mg H2O/L [ 34 ]. It is important to consider that the performance specifications provided by the manufacturers of HMEs are based on in vitro measurements when delivering moisture, using the ISO 9360 method [ 7 , 35 ].…”