The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

IS PASSIVE EXPIRATORY FLOW AND TIME DURING MECHANICAL VENTILATION VALUABLE IN ASSESSING THE EFFECTIVENESS OF BRONCHODILATOR THERAPY?

Christopher Williamson RTS, Samelia Green RTS, and Timothy Op't Holt EdD, RRT University of South Alabama Mobile, Alabama

PURPOSE: A decrease in active expiratory time and increases in peak and mid-expiratory flows are typically thought of as indicators of bronchodilator (BD) effectiveness. Very little is known about changes in these parameters in patients being mechanically ventilated, since their expiration is passive, rather than forced as they are during routine pulmonary function studies. The purpose of this study is to determine if these variables change following BD therapy in patients with chronic obstructive pulmonary disease (COPD) who are being mechanically ventilated.

Methods: Following hospital approval of the project, seven patients with COPD who were being mechanically ventilated by a Nellcor Puritan-Bennett 7200 ventilator and who were receiving BD therapy (2.5 mg Albuterol /NS ± 0.5 mg ipratropium bromide Q4 hours) were studied. COPD was diagnosed based on clinical history, physical findings, or pulmonary function tests according to the standards of the American Thoracic Society. BDs were administered for 30 minutes prior to suctioning by an in-line nebulizer approximately fifteen inches proximal to the ventilator circuit wye. Each patient remained in the Synchronized Intermittent Mandatory Ventilation + Pressure Support mode of ventilation throughout the study. For each patient, three pre- and 15 minute post-treatment flow-volume loops and flow-time waveforms from mandatory ventilations were printed. Flows were determined by extrapolation to the Y-axis of the loop followed by conversion to L/sec. Times were determined by measuring the length of expiration along the X-axis using a dial caliper followed by conversion to seconds. Changes in these parameters were analyzed using a one-tailed t test (a = 0.05).

Results: The mean pre- and post-treatment active expiratory times ± SD were 2.28 ± 1.02 sec. and 1.78 ± 0.63 sec. respectively (p=0.049). The mean pre- and post-treatment peak expiratory flows ± SD were 47.67 ± 11.47 L/sec. and 47.21 ± 12.79 L/sec. respectively (p=0.38). The mean pre- and post-treatment mid-expiratory flows ± SD were 28.59 ± 3.51 L/sec. and 28.55 ± 7.59 L/sec. respectively (p=0.49).

Conclusions: Changes in peak and mid-expiratory flow on passive pre- and post BD flow-volume loops were insignificant. However, the active expiratory time during passive expiration from a positive-pressure breath decreased significantly following BD therapy. Several conclusions may be made that warrant further study: 1. passive expiratory flows from positive-pressure tidal volumes are not sensitive to BD therapy, 2. the dose of BD is insufficient to cause a change in these values in the patients studied, 3. the patients studied do not respond to BD therapy due to the severity of their illness or 4. the number of patients studied was insufficient to detect a change. Therefore, this study is still in progress and more data will be obtained.

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