1995 OPEN FORUM Abstracts
Comparison Of Wob, Rise Time, And Pressure Overshoot During Psv With Two Ventilators
Richard D. Branson, R.R.T., Kenneth Davis, Jr., M.D., Jay A. Johannigman, M.D., Division of Trauma and Critical Care, department of Surgery, University of Cincinnati Medical Center, Cincinnati, Ohio
INTRODUCTION: Pressure support ventilation (PSV) has become a popular method of ventilatory support during weaning. We compared the PSV functions of two ventilators during simulated spontaneous breathing.
Methods: We simulated spontaneous breathing (SSB) using a two-chambered test lung at three tidal volume and flow combinations (200 mL at 30 L/min, 400 mL at 60 L/min, and 600 mL at 90 L/min) and at 0 and 5 cm PEEP. During SSB we connected the 2 ventilators (Bird TBird VS and Puritan-Bennett 7200ae) to the experimental chamber in the PSV mode at 15 cm H_2O. A pneumotachograph and pressure tap were placed at the proximal airway and measurements of pressure, volume, and flow were recorded to a personal computer using a data acquisition system (Keithley DAS 16). From these signals the WOB,, maximum negative pressure (Pmax), delay time (DT), and pressure time product (PTP) were calculated. We also calculated rise time (the time in seconds to reach 90% of the set pressure) and overshoot (the difference between actual peak pressure and set pressure).
Results: The WOB,, PTP, Pmax, and delay time were all significantly less with the TBird VS compared to the 7200ae (p < 0.05). Overshoot was significantly less in all situations. Rise time was faster with the TBird VS, except at the 600 mL and 90 L/min inspiratory flow. Table 1 shows data from SSB at 400 mL and 60 L/min.
Variable TBird VS7200ae
Delay Time (s) 0.09 (0.02)# 0.12 (0.02)
Pmax (cm H_2O) 1.0 (0.2)#3.6 (0.5)
WOB J/L)0.004 (0.001)# 0.020 (0.006)
PTP (cmH_2O/s) 0.03 (0.014)#0.15 (0.03)
Rise Time (s)0.21 (0.006)#0.34 (0.01)
Overshoot (cm H_2O) 0.57 (0.06)# 0.92 (0.04)
Pmax = maximum negative pressure; WOB = work of breathing; and PTP =
pressure time product. #p < 0.05 vs 7200ae.
Conclusions: Our results suggest that the TBird VS allows a lower WOB, and tighter control of set pressure support level compared to the 7200ae. The differences in these values is small and the clinical importance is unclear.