2005 OPEN FORUM Abstracts
EXHALATION VALVE RESISTANCE OF MODERN VENTILATORS WHILE VENTILATING AN ELECTRONIC LUNG SIMULATOR
Thomas J. Wing BS RRT, Candy Perry SRT, Lonny J. Ashworth MEd RRT. Boise State University, Boise, ID.
Background: Modern ventilators are used in critical care facilities across the world. The hypothesized resistance imposed by the exhalation valve (ER) placed upon the patient could lead to increased work-of-breathing and Auto-PEEP. Previous studies have evaluated the ER when ventilating a dual-lung model; however, no studies have examined the ER when the ventilator is connected to an electronic lung simulator.
Methods: Four ventilators were studied: Viasys Avea (VA), Drager Evita 2 (DE), Puritan Bennett 840 (PB 840) and Siemens Servo i (SI). Each ventilator was connected to a Hans Rudolph Series 1101 Breathing Simulator. PEEP values of 0-25 cm H20 and Tidal Volumes of 200-1200 mL were used. Pressure and flow were measured immediately before the exhalation valve; pressure after the exhalation valve was ambient. ER was calculated as (P1 - P2)/ V, where P1 = pressure immediately before the exhalation valve, P2 = 0 cm H2O reflecting ambient pressure, V = peak expiratory flowrate, in LPS, immediately before the exhalation valve.
Results: At PEEP 0-25 cm H2O and VT 200-1200 mL the values for ER (in cm H2O/L/second) were as follows: VA 5.5-159.1; DE 2.9-76.4; PB 840 4.3-104.4;
Conclusion: The range of ER varies considerably among ventilators and at a variety of set PEEP and VT. This study shows that the resistance is surprisingly elevated and should be taken into consideration on a patient-to-patient basis. Further trials are necessary in order to evaluate the impact of the elevated levels of ER in patients.