1999 OPEN FORUM Abstracts

LABORATORY EVALUATION OF ULTI-MIST HEAT AND MOISTURE EXCHANGERS

Richard Branson RRT, Robert Campbell RRT, Kenneth Davis Jr. MD Department of Surgery, University of Cincinnati Medical Center, Cincinnati, OH. 45255

Background: Hygroscopic heat and moisture exchangers (HHME) are frequently used to condition inspired gases during mechanical ventilation. We evaluated the moisture output (mg H2O/L), resistance (cm H2O/L/s), and deadspace (mL) of 2 new HHME and 2 new HHME filters (HHMEF). Method: A patient lung model consisting of a cascade humidifier, temperature controller, 2 test lungs, and a series of tubing and one-way valves to separate inspired and expired gases was constructed as per ISO 9360. The model was ventilated using compressed air at: 1) V_T = 500 mL and f = 20 b/min and 2) V_T = 1000 mL and f = 10 b/min. Ventilation was accomplished using a square inspiratory flow pattern and I:E of 1:2. The lung model was controlled to maintain an expired gas temperature of 34°C. The model was weighed before and after ventilation with and without the HHME in line to determine water loss in mg/L. Moisture output (MO) was determined using the equation (MO = 1 - [water loss in mg with the HHME/ water loss in mg without the HHME] ´ 37.6. Resistance was measured by delivering a flow of 1.0 L/s through the device via a rotameter and measuring the pressure drop with a differential pressure transducer. Deadspace was determined by filling the devices with water from a calibrated flask. Three of each device were tested.

Results: Results are shown in the table as mean ± SD.

MS-120 = Medisize Ulti-Mist HME ICU, MS-121 = Medisize Ulti-Mist HME/F ICU, MS-110 = Medisize Ulti-Mist HME ICU, MS-111 = Medisize Ulti-Mist HME/F ICU (King Systems, Nobelsville, IN)

Conclusions: New HHME(F) devices are introduced frequently. Evaluation of these devices using standard test protocols, allows independent comparison of device characteristics. The devices tested meet the AARC guidelines proposed in the Consensus Conference on Mechanical Ventilation. The HHMEF devices have a significantly higher resistance than the HHME devices, despite no increase in MO. No device exceeded the maximum resistance of 5 cm H2O/L/s suggested by ISO. RCP's should appreciate the characteristics of the HHME(F) devices they use.

OF-99-118