The Science Journal of the American Association for Respiratory Care

2012 OPEN FORUM Abstracts

AN EVALUATION OF INSPIRATORY PRESSURE ATTENTENUATION IN AN ARDS LUNG MODEL WITH THREE DIFFERENT ETT SIZES USING HIGH FREQUENCY PERCUSSIVE VENTILATION.

David Grooms1, Erin McCormick2; 1Sentara Norfolk General Hospital, Norfolk, VA; 2Tidewater Community College, Virginia Beach, VA

Background: Pressure attenuation is the diffusion of pressure, gas flow rate, and/or tidal volume during gas delivery. Using bulk flows (conventional ventilation), attenuation is higher as artificial airway size decreases. However, pressure attenuation associated with pulsatile flow delivery systems is not well understood because of the difference in breath delivery flow profiles. Method: Using a simulated ARDS test lung model (Michigan Instuments), pressure attenuation with high frequency percussive ventilation (HFPV) using the Percussionaire Volumetric Diffusive Respirator (VDR) was evaluated by using three different ETT sizes (6.0, 7.0, & 8.0). Phase 1: Pressure was measured distally (airway before ETT) and proximally (at the end of the ETT) using the Hamilton G5 (Bonaduz, Switzerland,) as a conduit for digital and graphical data capture. Phase 2: Pressure was measured distally (airway before ETT) and proximally (inside test lung) using digital and analog manometry. Pressure attenuation was measured to be the difference between distal and proximal measurements for all three airway sizes. The test lung settings remained constant at a airway resistance of 7 cm H2O/L/sec and static compliance of 17 ml/cm H2O for each airway type. VDR settings were set to target combination of analog peak inspiratory pressures (pulsatile flowrate-PIP) of 35, 45 & 55 cm H2O, with analog expiratory pressures (oscillatory CPAP/PEEP) measuring 5 & 10 cm H2O. Inspiratory and expiratory time was set to 2 seconds each, with a measured convective rate of 15bpm. Percussive rate was set at 500 bpm. Results: Phase 1: Pressure attenuation was observed with all airway sizes and did not differ significantly. Phase 2: Pressure attenuation was not observed when measuring pressure using analog manometry on the VDR (Fig 1). Conclusion: Using digital manometry, pressure attenuation was observed through all airway sizes. Using analog manometry (and validated with digital manometry), pressure attenuation was not observed. Therefore, analog measured pressure on the VDR can be assumed to reflect respiratory system pressure under these conditions in an ARDS lung model. Sponsored Research - None Figure 1. Pressure measurments of all three airway sizes during inspiration and expiration using pulsatile flowrate to achieve PIP of 355 cm H2O with oscillatory CPAP of 5 cm H2O.