The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

AN OBSERVATIONAL STUDY OF DISPLAYED INSPIRATORY PRESSURE WITH AND WITHOUT TUBE COMPENSATION WHILE USING ADAPTIVE SUPPORT VENTILATION

Timothy France1, David Grooms1



Background: ASV is a form of closed loop ventilation, which automatically adjusts inspiratory pressure (Pinsp), tidal volume (Vt) and rate in order to maintain minimum minute ventilation. ASV monitors the patient's compliance; resistance and alveolar time constants and adjust respiratory rate and Vt according to the Otis least work of breathing equation. Tube resistance compensation (TRC) is an addition to pressure breath types, which automatically adjusts inspiratory pressure levels in proportion to changes in inspiratory flow. The intent is to offset the flow resistive properties of artificial airways in order to maintain a constant carinal pressure throughout inspiration. ASV displays the current inspiratory pressure that is required to maintain the target tidal volume. We hypothesized that there would be changes in displayed Pinsp with and without TRC.

Methods: A total of 26 patients were ventilated and liberated in ASV mode. Fifty-six observations were performed in which data was collected. Data included Pinsp with and without TRC and expiratory time constants (Rcexp).

Results: On average the Pinsp increased by 1.9 cmH2O when TRC was disabled. However, larger increases to Pinsp were observed with higher baseline Pinsp levels (fig. 1).

Conclusion: While using ASV mode, the displayed Pinsp increased when TRC was disabled. Patients requiring lower Pinsp levels had smaller increases in Pinsp, while patients requiring higher Pinsp levels had larger increases in Pinsp.