The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

The Effects of High Frequency Chest Wall Oscillation on TIDAL Volume and Paco2 in a Swine Model of Acute Lung Injury

Michael A Gentile RRT, Donna S Hamel RRT, Damian M Craig MS, George A Quick, Ira M Cheifetz MD, Duke University Medical Center, Durham, NC

Background: The Vest™ airway clearance system (Hill Rom, St. Paul, MN) compresses and releases the chest wall through an inflation-deflation cycle that results in high frequency chest wall oscillation (HFCWO). This compression exerts pressure to the chest at a rapid frequency and may interfere with tidal volume (Vt) delivery while used in conjunction with Pressure Control Ventilation (PCV). We hypothesized that the external pressure exerted to the chest during PCV would not adversely affect PaCO2.

Methods: Twelve swine (10.3 ± 1.1 kg) with acute lung injury induced by saline lavage were ventilated with a Viasys Avea ventilator (Viasys Critical Care, Palms Springs, CA). Ventilator settings in the pressure control mode included: PIP adjusted to achieve Vt 10 ml/kg, respiratory rate 25, FiO2 0.6, PEEP 8 cmH2O, inspiratory time 0.50 seconds. Animals were randomized to either treatment with Vest +PCV or PCV alone. The Vest System was placed on animals at a pressure setting of 0.5 and frequency of 5Hz. All animals were ventilated for four hours. Tidal volumes were measured by a flow sensor (NICO; Respironics-Novametrix, Wallingford, CT) at the circuit wye. Data were analyzed by ANOVA with repeated measures.

Results: HFCWO + PCV resulted in lower delivered tidal volumes than PCV alone (p=0.0001). PaCO2 did not significantly differ (p=0.76).

  PaCO2 (torr) Tidal Volume (ml)
Vest 57 ± 15 4.7 ± 0.8
Control 47 ± 19 10 ± 1.8
p 0.76 0.0001


Conclusion: Despite the reduction in delivered tidal volume, PaCO2 remained stable during HFCWO. HFCWO in conjunction with PCV may enhance ventilation by allowing for acceptable CO2 elimination at lower delivered tidal volumes.

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