2002 OPEN FORUM Abstracts
INTER-RATER VARIABILITY IN ESTIMATING THE LOWER INFLECTION POINT (LIP) FROM PRESSURE-VOLUME (PV) CURVES GENERATED USING TWO DIFFERENT TECHNIQUES.
Robert S. Campbell RRT FAARC, Bradley R. Davis MD, Jay A. Johannigman MD, Kenneth Davis Jr. MD, Sandra L. Miller MD, Chris Blakeman RRT, Richard D. Branson RRT FAARC. University of Cincinnati College of Medicine, Cincinnati, OH.
BACKGROUND: The P-V curve may be used to determine optimal PEEP if a LIP is detected. Use of PV curves are not yet standard practice due to inconsistencies in generating and interpreting the curve. We investigated the variability of LIP estimation (LIP-e) by six clinicians using visual inspection of PV curves generated using two different techniques.
METHOD: Eight consecutive mechanically ventilated pts at risk for ARDS were studied. Each pt was placed on a Galileo Gold ventilator (Hamilton Med) which has a new automated PV maneuver (constant pressure rise) as part of a pre-clinical software package. Each pt was chemically paralyzed for the procedure and no pt had evidence of air leaks from chest tubes or ET tube. Automated PV curves (PV-A) were generated using a Pmax of 40 cmH2O and a pressure-rise of 2 cmH2O/sec. Pressure, volume, and flow were measured at the proximal airway using the Galileo flow transducer and data was recorded to a PC using available software package (Datalogger). Static PV (PV-M) curves were also generated on each pt using 100 ml aliquots from a calibrated syringe until airway pressure reached 40 cmH20. Data was similarly collected to the PC during each static PV maneuver. A minimum of four PV curves were obtained on each pt (two with each technique). PV curves were printed and distributed (in randomized order) to three intensivists and three respiratory care practitioners for estimation of LIP. The mean estimated LIP and standard deviation (SD) was determined and compared to a mathematically determined LIP (LIP-M= greatest compliance Æ).
Results: Forty PV curves were evaluated (20 PV-A, 20 PV-M). Mean LIP-e ranged from 7 to 19 cmH2O for the eight pts. Mean SD using PV-A was 2.3, with a max SD of 2.9 on pt 6. Mean SD using PV-M was 2.0, but SD exceeded 3.0 on pts 5, 6, and 7. Max diff in LIP-e from PV-A was 8 cmH2O for pt 6. Mean max diff using PV-A was 5.7 ± 1.2 cmH2O. Max diff in LIP-e from PV-M was 11 cmH2O for pt 6. Mean max diff using PV-M was 5.2 ± 3.9. Max diffs using PV-M were usually due to one reviewer estimate. LIP-e with PV-A was typically 1-2 cmH2O higher than PV-M. Mean LIP-e of all reviewers was within 2.5 cmH2O of the LIP-M on all but two occasions (-6 on pt 2 and +4 on pt 4, both PV-M). LIP-e was not identifiable on two occasion using PV-A and on five occasions using PV-M.
Conclusions: LIP-e varies widely between clinicians. Greater variation with PV-A may result from having more data points (>1400 versus < 25) resulting in a "smoother" curve. Determination of true LIP may be improved if PV is reviewed by multiple clinicians. Using PV curves to determine vent settings may be enhanced if an objective method of interpretation were available. Clinical effectiveness of setting PEEP at or above LIP on PV in terms of clinical outcomes, gas exchange and lung mechanics requires further investigation.