The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts


Stanley M. Baldwin1,2, Alan Alipoon1,2, Bud Spearman2; 1Respiratory Care, Loma Linda University Medical Center, Loma Linda, CA; 2School of Allied Health Professions, Loma Linda University, Loma Linda, CA

BACKGROUND: The Drager Evita Infinity V500 ventilator has an AutoRelease in Airway pressure Release Ventilation (APRV) mode that allows the operator to set an inspiratory trigger for inspiration for mandatory breaths which results in the transition to Phigh as a percent of peak expiratory flow (%PEF). This setting determines Tlow which is the release time (expiratory time) and indirectly the intrinsic PEEP (PEEPi) and End Expiratory Lung Pressure (EELP). APRV is an open lung strategy to recruit and maintain open alveoli with out the use of set PEEP which may retard expiratory flow and ventilation. The purpose of this study was to determine the effects of % PEF when set by AutoRelease on end expiratory lung pressure ( EELP), exhaled tidal volume ( VT) and mean airway pressure (mPAW) under varying conditions of compliance and resistance. METHODS: A passive patient was simulated using a Michigan Test Lung (TL). The ventilator was set initially at Thigh=5.0 sec., Tlow=0.5 seconds, Phigh=30 cm H2O, Plow=0 cm H2O. Baseline measurements were made of mPAW, VT, EELP and PEEPi . Measurements were repeated with the AutoRelease set at 50% and 70% under varying conditions of compliance and resistance. The TL was set to simulate four patients using combinations of resistance (R) and compliance (C). These included equivalent (1) C=0.05L/cmH2O and R=9mmID, (2) constant R=9mmID and variable C=0.02L/cmH2O, (3) constant C=0.05, and variable R=5mmID, and (4) variable C=0.02L/cmH2O and variable R=5mmID. RESULTS: See Table 1 CONCLUSION: Intra-comparisons under varying simulated compliance and resistance had little effect on mPAW from 50% -70%. There was a larger change seen on Vt and minute ventilation using Auto release from 50% to 70% under the simulated patient's with various changes in compliance and resistance. Even though mMAP was fairly stable, there were large variations in EELP. * One problem with Auto Release we were unable to measure PEEPi due to the ventilator releasing PEF to baseline to measure trapped lung volume. This has the potential for inadvertent lung de-recruitment. Sponsored Research: Ventilator was loaned for the period of study.
Sponsored Research - Drager Ventilator was loaned for the bench study
Table 1. Data comparisons of 50% vs. 70% Auto Release of the four varying lung conditions