2004 OPEN FORUM Abstracts
EFFECTS ON TIDAL VOLUME WHEN CHANGING FROM A HEAT AND MOISTURE EXCHANGER (HME) TO A CONCHATHERM HEATED HUMDIFIER USING A STANDARD CONCHA-COLUMN
Theodore Stryker, BA, RRT,
University of Washington Medical Center, Seattle, WA
Background: Many
ventilators do not automatically compensate for compressible volume.
The volume lost must be added to the ordered tidal volume. At our
institution, HMEs are the primary method of humidification. As a
patients condition warrants, active humidity is provided by using the
CONCHATHERM
system (Hudson RCI, Temecula, CA). We have recently become aware that
the addition of necessary hardware (water traps, CONCHA-COLUMN
and reservoir) for active humidification changes the tubing
compliance and, therefore, the delivered tidal volume. This change
in tubing compliance was noted to increase as the water reservoir
emptied. We attempted to measure the effects this changing compliance
had on a delivered tidal volume.
Methods: Each of the test
ventilators (Servo 300, Maquet, Inc. Bridgewater, NJ) was configured
in the same manner in which they would be used with low compliance
re-useable HYTREL
(Maquet, Inc.) circuits. A CO2SMO
Plus Respiratory Profile Monitor (Novametrix Medical Systems Inc.,
Wallingford, CT) measured pressure and volume at the patient wye. A
Servo test lung 190 was used as the test lung. Measurements were
taken with an HCH (Humid-Vent Filter
Light, Hudson RCI, Temecula, CA) and no water traps. Water traps and
CONCHATHERM were
then added and measurements obtained with full and empty reservoirs.
The circuit temperature was allowed to warm up to 30°C.
Tubing compliance factors were calculated by adjusting the tidal
volume to obtain a static pressure of 50±cm
H2O with no peep and end-inspiratory pause of 1second.
Compliance was calculated as Tidal volume/Static pressure.
Results: The
tubing compliance factor increased from 1 cc/cm H2O to 3
cc/cm H2O when changing from HCH to CONCHATHERM.
Median tidal volume reduction was 16 percent (range 10 to18). When
the water reservoir was empty, the tubing compliance factor had
increased to 4 or 5 with a median tidal volume reduction of 27
percent (range 21 to 31) as compared to the HCH. As tidal volume
decreased, static pressures also decreased.
Conclusions: In
using a low compliance circuit, corrected tidal volumes should be
recalculated when switching from an HCH to CONCHATHERM
active humidification. The use of a standard CONCHA-COLUMN
will result in the tidal volumes changing over time. This will also
occur on ventilators that automatically compensate for compressible
volume. The use of a low compliance CONCHA-COLUMN
may result in less variation in tidal volumes.