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.