2004 OPEN FORUM Abstracts
COMPARABILITY OF THE ACTIVE SERVO LUNG 5000 SIMULATOR WITH A PNEUMOTACHOMETER/ PRESSURE TRANSDUCER SYSTEM
Ghazi
Alotaibi, MS, RRT (University of Medicine and Dentistry of New
Jersey, Newark, NJ); Craig Scanlan, EdD, RRT, FAARC (UMDNJ,
Newark, NJ); Robert Kacmarek, PhD, RRT, FAARC (Massachusetts
General Hospital and Harvard Medical School, Boston, MA); Al Heuer,
PhD, RRT (UMDNJ, Newark, NJ).
BACKGROUND: Most ventilator bench testing is conducted on bellows/spring
lung
models, with key variables measured by pneumotachometer and pressure
transducer (PnPT), interfaced with data acquisition hardware and
software. The Active Servo Lung 5000 (ASL; Ingmar Medical,
Pittsburgh, PA) integrates all these components into a single
computer-controlled device that could serve as a new standard for
ventilator testing. Unfortunately, there is no performance data yet
published on this device. To address this limitation, we assessed
whether the ASL's primary measures (pressure and volume) were
comparable to those obtained via a calibrated PnPT system.
METHOD: A
method agreement study was conducted using the approach recommended
by Chatburn (1996), with data analysis based on that of Bland and
Altman (1999). Acceptable levels of ASL repeatability (repeatability
coefficient or RC), average bias between methods, and method limits
of agreement (LOA) were set a priori for pressure (RC = 0.5 cm
H2O; bias = ±2 cm H2O; LOA =
no differences > ± 2SD of
bias) and volume (RC = 5 mL; bias = ±20
mL; LOA = no differences > ±
2SD of bias). The PnPT system was calibrated using a standard 2-point
procedure for pressure, flow and volume, with all data signals
digitized and recorded using WINDAQ software. The calibrated PnPT
system was then placed in line with the ASL and 15 observations of
two breaths each were obtained over a range of pressure (10-55 cm
H2O) and volume (200-900 mL), with simultaneous recording of PnPT and
ASL 5000 data. RESULTS: The repeatability coefficients for the ASL's
measurements were 0.10 for pressure and 1.50 for volume, both
superior to the PnPT system. Pressure and volume bias and LOAs
between these two systems, including their 95% confidence intervals
(95% CI) are reported in the following table.
| Measurement | Bias (95% CI) | Limits of Agreement | |
| Upper (95% CI) | Lower (95% CI) | ||
| Pressure cm H2O | –0.83 (± 0.49) | 0.74 (± 0.75) | -2.41 (± 0.75) |
| Volume mL | 13.14 (±1.62) | -3.83 (± 8.16) | 30.11 (± 8.16) |
Bland-Altman
plots revealed that all volume observations were within their
expected LOA, but that one pressure observation (mean P = 54.62 cm
H2O; P= -2.53 cm H2O) fell
outside its expected LOA. However, these plots also revealed
systematic trends in measurement bias between the two systems.
Pressure bias trended positive (ASL > PnPT) at low pressures and
negative (ASL < PnPT) at high pressures. Volume bias was always
positive (ASL > PnPT), with a trend toward greater volume
differences at progressively higher volumes.
CONCLUSIONS: As compared
to the traditional PnPT ventilator bench test standard, the ASL
exhibits good repeatability and acceptable bias and levels of
agreement within the range of pressure and volume commonly
encountered with adult patients. Systematic trends in measurement
differences indicate the potential need for correction formulae when
interpreting data obtained between these systems.