2002 OPEN FORUM Abstracts
USING PROXIMAL PRESSURE MEASUREMENTS TO DETERMINE OPENING PRESSURE DURING HIGH FREQUENCY PERCUSSIVE VENTILATION
Dean Holland RRT, Bob Estetter RRT, Jason Higgins BS RRT, Ken Hawkins BS RRT, Parkland Health and Hospital System, Dallas, Texas, Department of Respiratory Care
Introduction High frequency percussive ventilation (HFPV) has been shown to decrease mortality and improve oxygenation in the adult population by integrating bulk gas movement (tidal volume) with high frequency pulses. However, optimizing ventilator settings from initiation through weaning can be challenging even for the experienced clinician. We hypothesize that opening pressures can be identified by monitoring changes in proximal pressure (DP) inside the phasitron (sliding venturi).
Methods A multiple balloon lung model was attached to a Volumetric Diffusive Respirator (VDR) by means of a # 8 I.D. ETT. The lung model was submerged in a fifty-gallon aquarium and fixed at two different levels. A slow-flow (four lpm) pressure-volume curve was performed at each depth. Lower inflection points (LIP) were identified at 12.5 cmH2O and 21.4 cmH2O with a statistical software program (STATA). For the purpose of this work we associated the values obtained for LIP?s as representative of opening pressures. The VDR was set with expiratory time to max (infinity), oscillatory PEEP of 8 cm H20, pulse frequency 400, and i/e of 9 (set on the dial). These settings were held constant throughout data collection. Total PEEP (TP) was defined as the sum of the oscillatory and demand PEEP level. For each group the demand PEEP was initiated at 0 cmH2O and increased in increments of 3 cmH2O until the total pressure exceeded LIP. Data was collected at each level of demand PEEP for both groups. Measurements were captured using a differential pressure transducer connected to the proximal sampling port of the phasitron and interfaced through a space lab monitor (model 90603A). DP was defined as the difference between the peak and trough of oscillations.
Discussion This work suggests that LIP can be determined by measuring pressure changes inside the phasitron and proximal to the ETT. We believe that these results represent an initial step toward understanding the complex aspects of gas movement within the phasitron during HFPV. Further, application early in a patient?s acute phase will decrease the potential for VILI secondary to cyclic tidal opening and closing of alveoli. We recognize additional investigation is needed to optimize HFPV settings in the clinical setting. We believe that future investigations should focus on of quantifying the response of the phasitron (sliding venturi) to mechanical factors within the lung.