The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

Bench Test of Dräger E4 Ventilator with Helium-Oxygen Mixtures

John Newhart RCP, Craig Pedersen RCP, Timothy Morris M.D. UCSD Medical Center, San Diego CA

BACKGROUND: We have used the Dräger Evita 4 ventilator to deliver helium oxygen mixtures (HeO2) to mechanically ventilated patients at our institution for 2 years. HeO2 is used to treat patients with upper airway obstruction by promoting laminar flow past the obstruction thus reducing the work of breathing. This may also improve the distribution of ventilation. Administering HeO2 mixtures through an ICU type ventilator requires an understanding of how helium effects the gas delivery characteristics of the ventilator. HeO2 mixtures of 80%/20% have a lower density than air (80/20HeO2-.429g/L vs. Air-1.293g/L), affecting ventilator function. The heat carrying capacity of He is also greater than air causing hot wire flow sensors in the ventilator to overestimate derived volumes. We sought to determine HeO2 effects on ventilator function relative to accuracy of volume and FIO2 delivered.

Methods:
All testing was done with the ventilator in PCV mode (open breathing system), adult range. Volumes were measured with a Bio Tek VT1 (Winooski, VT) test lung. Oxygen was measured external to the ventilator with an electrochemical type (Mini-Ox I, MSA, Pittsburgh, PA) analyzer. The hot wire exhalation flow sensor was removed due to its incompatibility in measuring He mixtures.

Results:
Using an 80/20 HeO2 mixture connected to the air inlet of the ventilator, we found the measured volumes to be consistent regardless of the oxygen concentration delivered. The ventilator O2 monitor was within 1% of the external analyzer.
CONCLUSION: The ventilator O2 monitor was accurate and should be used to attain the desired FIO2 instead of the O2 setting control. Inspired volumes displayed on the ventilator when using HeO2 varied significantly from actual and should not be used for clinical assessment. Based on our limited lab evaluation and clinical experience, we feel that 80/20 HeO2 can be safely used in the Dräger E4 in adult mode using PCV when flow monitoring is turned off, and the flow sensor is removed. Further testing will include effects on volume control mode, pressure support, rise time, sensitivity and pediatric mode. (See Original for Figure)

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