The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

THE EFFECT OF A HELIUM/OXYGEN MIXTURE ON THE ACCURACY OF TIDAL VOLUME MEASUREMENTS OF MECHANICAL VENTILATORS.

Michael A. Gentile, RRT, John M. Davies, RRT, Robert R. McConnell, RRT, Ira M. Cheifetz, MD, Duke University Medical Center, Durham, NC.

Background: The use of Helium/Oxygen mixtures (Heliox) may be useful when treating patients with airway obstructive disease due to its lower density. We hypothesized that Heliox would have an effect on the tidal volumes (Vt) measurements of various mechanical ventilators based upon the different technologies used to measure Vt.

Method: We performed bench evaluations on four ventilators: Puritan-Bennett 7200ae, Seimens Servo 900c, Bird 8400sti, and Bear 1000. All four ventilators were connected to a test lung and placed in the Assist Control Mode, with set tidal volume 500 ml, rate 20 breaths per minute, FiO_{2} 30%, PEEP 5 cm H_{2}O, and a square-wave inspiratory flow pattern and. An external monitoring device (Cosmo Plus!, Novametrix) which could be adjusted for various gas densities was placed in line. The first tests were done on a standard hook up to wall air and oxygen with a set FiO_{2} of 30%. The ventilators were next tested with the air supply hose attached to a Heliox tank (70% Helium/30% Oxygen) set at 50 PSIG. Each ventilator served as it own control.

Results:

Air/Oxygen Heliox

Ventilator Expired Vt Expired Vt Difference

PB 7200ae 460 ml 1000 ml + 540

Servo 900c 481 ml 479 ml -3

Bear 1000 500 ml 3680 ml + 3180

Bird 8400sti 464 ml 478 ml +14

Conclusions: Gases with lighter densities than air have a varied effect on mechanical ventilators. It is important to the clinician to be aware of how different gas densities will effect the function of the ventilators. If the clinician is using a ventilator that is effected by Heliox, it may helpful to have an external monitoring device which can be adjusted for various gas densities verify exhaled tidal volumes.

The 44th International Respiratory Congress Abstracts-On-DiskĀ®, November 7 - 10, 1998, Atlanta, Georgia.

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