# 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.

**OF-02-171**