The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

Pressure ATTENUATION during high frequency oscillatory ventilation: A bench study

Matthew J Branconnier RRT, John D Davies RRT, Michael A Gentile RRT, Ira Cheifetz MD FAARC.

Background: The use of high frequency oscillatory ventilation (HFOV) has steadily increased for adult patients with acute respiratory distress syndrome (ARDS). Unlike traditional mechanical ventilation, measuring the pressure delivered to the lung is difficult with HFOV. The purpose of this study is to quantify the pressure attenuation which occurs in the delivered gas during HFOV.

Methods: The SensorMedics 3100B Oscillator (Viasys Healthcare, Palm Springs, CA)was connected to a test lung (TTL, Michigan Instruments Inc., Grand Rapids, MI), with a compliance of 0.05 l/cm H2O through a 6.0 mm endotracheal tube. Ventilator settings included: frequency 5 Hz, inspiratory time 33%, and FiO2 0.40. Pressure measurements at the humidifier inlet, patient wye, and test lung were obtained with a RT-200 Calibration Analyzer (Timeter Instrument, Lancaster, PA). Data were collected in all combinations of the following ventilator settings: bias flow of 40 and 30 l/min, mean airway pressure (Paw) of 40, 35, 30, and 25 cm H2O, and power setting of 10, 9, 8, 7 and 6. Thus, results were obtained for 124 combinations of HFOV settings.

Results: The mean decline in pressure from displayed amplitude to lung was 76 ± 8 cm H2O (range: 24 ± 5 to 100±11 cm H2O). The most significant mean decrease occurred between the humidifier and the patient wye (34 ± 7 cm H2O).

Conclusions: Our bench study helps to quantify the attenuation of the pressure delivered during HFOV. In support of the theory of high-frequency ventilation, the actual pressure oscillation which reaches the lung is a small fraction of the pressure delivered from the ventilator.

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