The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

Performance of a Heat & Moisture Exchanger Designed to Allow Aerosol Delivery

Richard Branson, MS, RRT, Jay A. Johannigman MD. University of Cincinnati, 231 Albert Sabin Way; Cincinnati, OH 45267-0558

Background: The use of heat & moisture exchangers (HME) during mechanical ventilation has become routine. One contraindication for HME use is the need for aerosol therapy using a nebulizer and/or MDI during mechanical ventilation. We evaluated a new prototype HME which utilizes a bypass-valve to allow intermittent aerosol therapy and/or in-line MDI.

Description: The prototype HME (Thayer Medical) uses a traditional foam media. A by-pass valve, which is controlled by the caregiver, can be open (to allow aerosol through the center of the device) or closed (forcing inspired and expired gases through the media).

Method: Using the method described in ISO 9360 we evaluated moisture output, deadspace, and resistance of the HME (one treated with hygroscopic material, the other untreated). Moisture output was calculated using the gravimetric method at a VT of 500 mL and 1000 mL. Resistance was measured prior to use and after 2 and 24 hours in the model. Resistance was determined by directing flow at 1 L/s through the HME and measuring pressure drop (Timeter RT-200) across the HME. Each device was tested twice. We also evaluated resistance after 24 hrs of use in the model using a neblulizer to deliver 0.5 mL/5 mL of albuterol/saline every 2h.

Results: Data are shown I the table for a VT of 500 mL x 20 bpm.

Device Moisture Output 500/1000ml (mg H2O/L) Dead space (mL) Resistance (cm H2O/L/s)
Pre use 2 hrs 24 hrs 24hrs (q 2h aerosol)
Untreated 30.1/28.2 91±3 0.46 0.77 1.1* 1.3*
Untreated 30.9/28.6 90±2 0.55 0.80 1.4* 1.5*
Treated 33.1/30.1 90±2 0.54 0.93 1.3* 1.6*
Treated 32.7/29.8 89±1 0.61 0.99 1.5* 1.6*

All data are raw or mean ± SD, *p ≤ 0.05 compared to pre-use.

Conclusion: The prototype HME performs comparatively to current HME’s with respect to moisture output. Resistance is increased with duration of use and with aerosol delivery q 2 hrs. The difference between resistance with and without aerosol therapy was not statistically significant. Deadspace must be considered when using this HME during low VT ventilation.

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