2002 OPEN FORUM Abstracts
Laboratory Evaluation of an Automated Pressure-Volume Curve Maneuver
Robert S. Campbell, RRT, FAARC; Bradley R. Davis, MD; Jay A. Johannigman, MD; Kenneth Davis, Jr., MD; Sandra L. Miller,MD; Richard D. Branson, RRT, FAARC; University of Cincinnati College of Medicine, Cincinnati, OH.
Background: The pressure-volume (P-V) curve describes the mechanical properties of the respiratory system. Current techniques for P-V curve measurement include the supersyringe technique, multiple occlusion technique, and low-flow technique. The Galileo gold ventilator (Hamilton) incorporates an automated PV maneuver (pre-clinical software) that uses a constant pressure rise, which is adjustable between 2 and 5 cmH2O/sec. We evaluated the accuracy and reproducibility of this automated PV maneuver in the laboratory.
Method: We designed a bench study to evaluate the accuracy and reproducibility of the automated PV maneuver using the Galileo. We also assessed Galileo's ability to deliver the set pressure rise and any effect of varying lung mechanics. Five automated PV curves were performed on one side of a two-chamber test lung (TTL) for each of eight combinations of resistance (5 and 20 cmH2O/L/sec), compliance (20 and 50 ml/cmH2O), and pressure rise setting (2 and 5 cmH2O/sec). Pressure, volume, and flow delivery was measured at the prox airway at a sampling rate of 70/sec and recorded to a PC with commercially available monitoring package (Datalogger), from which, PV and Pressure-Tim (PT) curves wee generated. The measured PT curve was plotted against a mathematically determined curve and any deviations were noted. Peak and mean flowrate during each maneuver were also measured and recorded. Three manual PV curves were performed at each combination of R and C using 100 ml aliquots from a 0.5L calibration syringe. Automated and manual PV curves were overlapped and any deviations noted.
Results: Figure 1 reveals the overlapped automated and manual PV curves. Figure 2 reveals the PT curves plotted against the mathematically determined PT curve. Pressure rise setting of 5 cmH2O/sec at high C resulted in a mean flow >14 L/min. Mean flow at all other combinations was ² 6 L/min. The PT curve of the automated PV curve deviated from the mathematical curve (undershoot) in the first 0.8 seconds of the maneuver. Reproducibility of the automated PV curve was excellent. There was good correlation between the automated and manual PV curves.
Conclusions: The automated PV curve maneuver on the Galileo Gold ventilator yields reproducible and accurate measurement of lung mechanics. Benefits associated with use of an automated PV measurement include elimination of interoperator variability, faster completion of the maneuver, and avoidance of patient-ventilator disconnection. Clinical evaluation of the automated PV maneuver appears warranted.