2006 OPEN FORUM Abstracts
COMPARING SLOW-FLOW P-V LOOPS USING THE AVEA, DRÄGER XL AND GALILEO
Lacey Matteson, Rebecca Brollier,
Background: Pressure-volume (P-V) loops may be used to determine lower inflection points (LIP), upper inflection points (UIP) and a deflation curve. Slow-flow P-V loops of less than 9 LPM have been shown to produce curves similar to the traditional method of determining P-V loops. Some medical manufacturers provide an option allowing automated, slow-flow P-V loops. The purpose of this study was to compare the automated, slow-flow P-V loops of three different ventilators when connected to an electronic breathing simulator.
Method: Each ventilator was connected to the IngMar Medical Active Servo Lung 5000 (ASL 5000). Pressure and flow were measured between the patient wye and the lung simulator; volume was calculated and the pressure-volume loop graphed using a spreadsheet. The ASL 5000 was programmed to have an LIP of 15 cm H2O at 50 mL and an UIP of 30 cm H2O at 600 mL. The Viasys Avea, Hamilton Galileo and Dräger XL were evaluated. The Galileo has two slow-flow P-V loops: P-V 1 does not reduce expiratory flowrate, but P-V 2 does reduce expiratory flowrate. The Dräger XL provides slow-flow on inspiration only, or inspiration and expiration. The Avea provides slow-flow on inspiration only. Ventilator settings were selected to provide a similar maneuver. Avea settings: VT 0.8 L, Flow 4 LPM, PEEP 0 cm H2O, PEEP Teq. 1 second, sensitivity 3.0 cm H2O. Galileo settings: PSTART 0 cm H2O, PTOP 50 cm H2O, End PEEP 0 cm H2O, Ramp 5 cm H2O (approximately 4.5 LPM.), TPAUSE 0 seconds, TMANEUVER 20 seconds. Dräger XL settings: PSTART 0 cm H2O, PLIMIT 40 cm H2O, Flow 4 LPM, VLIMIT 0.8 L. Ten breaths were delivered between each P-V loop maneuver; this was repeated three times on each ventilator.
Results: During inspiration the P-V loop using all three ventilators had a similar LIP and UIP. The Galileo and Avea had similar inspiratory tracings, however, the Dräger XL revealed oscillations in pressure throughout inspiration. During expiration the tracings on the ventilators were not similar. The Avea does not restrict expiratory flowrate and demonstrated marked hysteresis. When using P-V 1 on the Galileo, the hysteresis was more than the Avea, but was reduced using P-V 2. On the Drager XL when using slow-flow on inspiration only, the hysteresis was less than with the Avea or Galileo P-V 1; the hysteresis was further reduced when using slow-flow on inspiration and expiration.
Conclusion: Performing slow-flow P-V loops with the electronic lung simulator using different ventilators produces varying results. There were obvious differences when P-V loops were performed with slow-flow only during inspiration; these maneuvers showed an increase in hysteresis. If the ventilator provides a controlled, slow-flow throughout expiration, hysteresis will be reduced.