2007 OPEN FORUM Abstracts
RELEASE VOLUME COMPARISON DURING AIRWAY PRESSURE RELEASE VENTILATION IN NEW-GENERATION ICU VENTILATORS
K. Miller1, A. Brown1, R. Smith1, S. Scott1
Introduction: Airway Pressure Release Ventilation (APRV) is utilized as a ventilatory strategy on patients with acute lung injury. During the initial institution of APRV, the ventilatory parameters are set to deliver a good chest rise and ensure optimal gas exchange. Accurate and reliable ventilator feedback is essential to maximize gas exchange. One of the parameters that are assessed during APRV is the release volume, which occurs at end expiratory flow. Release volume can be indicative of alveolar recruitment and airway stability.
Purpose: To evaluate and compare the release volumes of five different new generation ICU ventilations during APRV. We will also determine if ventilatory extension, similar to Automatic Tubing Compensation (ATC), affects the release volume.
Methods: Release volumes will be evaluated at three different compliance levels in five new-generation mechanical ventilators: Dräger Evita, Puritan Bennett 840, Hamilton Galileo, Maquet Servo-I, and Viasys Avea. The release volumes will also be evaluated after ventilatory extensions are activated. All results will be performed with the Michigan Lung Simulator. Release volumes will be measured at the following Phigh settings of 36cm H2O, 32cm H2O, 28cm H2O, 24cm H2O, and 20cm H2O. The Thigh will be set at 5.2 seconds and the Plow of zero. The expiratory flow (Tlow) will be adjusted to maintain a mid-expiratory flow of approximately 50% and rise time at maximum gas flow. Release volumes will be measured at the three different compliance levels along with three different resistance levels and then repeated with the ventilatory extension activated.
Results: There was no significant difference in the five ventilators during the APRV settings with the ventilatory adjuncts deactivated. However,when ATC was activated on the Dräger Evita 4 ventilator,we observed an increase in airway pressure and volume released. This has the potential of inducing lung injury. The NPB 840 could not maintain a constant airway pressure when the compliance was low and resistance was high (a very stiff and diseased lung). The Galileo, Avea, and Servo-I demonstrated consistent data collection and performance.
Conclusion: Inconsistent release volumes from different ventilators could potentially result in misjudgment of clinical end-points. Clinicians must be aware of the effects of when ventilatory adjuncts are activated. More research must be performed in order to fully understand the complexity of todayâs ventilators.