The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

COMPARISON OF THE MEASURED Vs. CALCULATED TIDAL VOLUME IN THE BENCH TOP STUDY USING PIPER-IPPB

Shawan Huff, RRT; Mercy General Hospital, Sacramento, CA, USA

BACKGROUND: Intermittent Positive Pressure Breathing (IPPB) is a technique used to provide short-term or intermittent mechanical ventilation for the purpose of augmenting lung expansion, delivering aerosol medication, or assisting ventilation[1]. To assess the therapeutic efficacy of an IPPB treatment, tidal volume may be measured. This study compares the measured tidal volume and the calculated tidal volume of the Piper-IPPB device.

Methods: The Piper-IPPB is connected via a custom adapter to a Wrights Respirometer Mark 14 and then to a Michigan Instruments Inc. Vent Aid TTL. Timing is accomplished using a Sportline Alpha 1 410 Splitimer. A Timeter flow meter is connected to a 50-PSI air source and 40 LPM is supplied to Piper-IPPB nebulizer. The inspiratory time is controlled by adjusting PIP and lung compliance. For ten breaths cycles both I-time and delivered tidal volume are summed and averaged. Fifteen points are collected and the average tidal volumes obtained. The calculated tidal volume is obtained using the calculation (I-time x Flow = Tidal Volume). Flow = 40 LPM

Results: The average measured and calculated tidal volumes are summarized below.

I-time (Seconds) Meas. Vt (L) Calc. Vt (L) % Difference
1.0 .565 .663 15%
1.2 .707 .829 15%
1.5 .862 1.033 17%
1.9 1.157 1.290 10%
2.2 1.210 1.451 17%

DISCUSSION: To assess the therapeutic efficacy of an IPPB treatment, tidal volume may be measured. Handheld spirometers and venticomp bags are two of the volume measuring devices currently used. Tidal volume can also be calculated using the calculation (I-time x Flow). There is only an approximate 15% difference between the measured tidal volume of the Piper-IPPB and the calculated tidal volume. This may be due to inherent leaks or timing errors.
CONCLUSION: Since there is only an approximate 15% difference between the calculated and measured tidal volumes, The calculated value may be a more efficient and cost effective way to monitor patient tidal volume when giving IPPB treatments. Further studies are warranted.
Supported by VORTRAN Medical Technology 1, Inc.
[1] Agency for Health Care Policy and Research (AHCPR). Health Technology Reports: intermittent positive pressure breathing (IPPB) therapy. 1991, Number 1.

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