1995 OPEN FORUM Abstracts
Evaluation Of Three Adult Pressure-Support Ventilator Response Times
Paul Holbrook, CRTT, Children's Hospital and Health Center, San Diego; Shari Ropelato, RRT, Hoag Memorial Hospital, Newport Beach CA; Jeff Child, RRT, McKay-Dee Hospital and Medical Center, Ogden, UT.
We postulated that appropriately applied pressure triggering could be as responsive to patient effort as flow triggering. To test this theory, we evaluated the responsiveness of three adult critical care ventilators to a relatively weak inspiratory effort.
Methods: Response time (Tr) for our purposes was defined as the interval between pressure rise in the drive compartment and the return to baseline pressure from a negative deflection in the dependent compartment of a two-sided Michigan Instruments test lung. A Newport E100 connected to the drive compartment was set to generate a peak inspiratory flow of 25 LPM in the dependent lung to simulate weak adult efforts. A dual-channel recorder allowed comparison of simultaneous pressure signals at the proximal pressure port of each ventilator circuit. The same adult circuit was used to test all ventilators. Compliance of dependent compartment was set to 55 mL/cmH20. Lung model was then connected to 6mm and 8.5 mm ETT. The Puritan-Bennett 7200, Siemens SV300, and Newport E200 were tested at pressure support levels (PSV) of 3, 10, and 20 cmH20 at CPAP of 5 cmH20. The 7200 was tested in both pressure (PT) and flow (FT) triggering. Sensitivity was maximized in each ventilator while avoiding auto-trigger problems. 7200FT was tested at flow-by of 5LPM, sensitivity of -1LPM.
Results: Data are presented for each ETT size and PSV level as mean (SD).
6.0 ETT 7200PT 7200FTSV300 E200
PSV399.5 (4.2)115.9 (7.86) 68.0 (3.35) 44.1 (1.95)
10118.6 (6.7) 114.0 (1.35) 75.1 (2.32) 45.9 (2.03)
2063.4 (7.0)117.5 (7.52) 90.9 (3.17) 42.8 (2.0)
PSV 3 75.5 (11.1) 129.9 (7.3)97.6 (3.76) 44.2 (2.78)
1064.3 (7.74) 124.6 (1.24) 69.0 (0.61) 45.9 (2.03)
2075.1 (5.69) 93.6 (4. 9)80.2 (1.71) 41.9 (6.42)
The E200 and the 7200 performed best at PSV of 20 cmH20. SV300 performed best at PSV of 10 cmH20. Generally, performance was better at PSV greater than 3 cmH20. 7200PT performed better than 7200FT. CONCLUSION: Significant differences exist between brands of ventilators. 7200PT probably performs better than 7200FT due to the ability to make smaller incremental changes in sensitivity, although these findings do indicate the need for further study. Continuously adjustable pressure triggering coupled with proximal pressure monitoring minimizes Tr.