The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

COMPARISON OF AIRTRAPPING BETWEEN HFPV HIGH FREQUENCY PERCUSSIVE VENTILATION AND PCV PRESSURE CONTROL VENTILATION WHILE UTILIZING A CLOSED SUCTION SYSTEM

K. Miller1, S. Pyne1, A. Brown1, R. Smith1


Introduction:Due to accumulation of oscillatory sub-tidal volumes and passive exhalation, High Frequency Percussive Ventilation (HFPV) may have a potential of airtrapping in the presence of an airway obstruction when utilizing a closed suction catheter. Hypothesis:During HFPV airway pressure is attenuated as resistance is increased. As the catheter is introduced within the endotracheal tube(ETT) pressure should be further attenuated with mitigation of air trapping distal to the suction catheter. Graphic analysis of volume,flow and pressure measurements in a laboratory setting will show no difference in the incidence of airtrapping between HFPV and PCV.

Methods:The VDR-4 (PERCUSSIONAIRE Corporation®, Sandpoint,Idaho) was used for HFPV and the Dräger Evita 4 (Dräger Medical Telford,Pennsylvania) was used for PCV. Settings were maintained at the same peak inspiratory pressure (PIP) 34 cmH2O,Positive end expiratory pressure (PEEP)14 cmH2O,Oscillations for HFPV were 500/minute. Monitoring was done with the Michigan Lung Dual Adult Model 1600 (Michigan Instruments,Grand Rapids Michigan) Suction duration was 15 seconds. Flow,Pressure,and Volume time graphs were recorded. Pressure/Volume and Flow/Volume loops were also recorded prior to catheter placement and with the catheter left in the endotracheal tube. Airway pressures were allowed to stabilize.

Results:
During the 15 second suction pass expiratory flow failed to return to base line before the next breath was given during PCV. In HFPV expiratory flow appeared unaffected. The suction catheter was left in the endotracheal tube with pressures allowed to stabilize; convective tidal volume in HFPV fell by 80cc, and by 20cc in PCV respectively. Variations in volume created from the oscillations could not be assessed. Discussion:The volume and flow characteristics created by the 500 oscillations are unique to HFPV. Flow-time graph monitoring reveals expiratory flow returning to base line during a regular suction pass with HFPV and not with PCV. The role oscillatory volumes may play in preventing airtrapping is unclear. Bench testing is static and not a dynamically changing physiological model as a patient receiving mechanical ventilation.

Conclusion:Our study demonstrates that the incidence of air trapping based on expiratory flow would be less for HFPV than for PCV when utilizing a closed suction system. Clinical trials are needed to observe patients for potential compromise while using closed suction systems with HFPV.

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