GE HEALTHCARE E-PSMP, Техническое руководство

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Cardiac Output Modules, E-COPSv, E-COP
4 - 3
2062973-004
Figure 2 Cardiac output measurement curve
A = area derived by integration of the time-temperature curve.
C = area beneath the time-temperature curve between t
30
% and end of the curve.
Computation based on an exponential fit to the curve between t
80
% of the peak and t
30
%.
REF (right ventricular ejection fraction) measurement is a part of the time-temperature
(thermodilution) cardiac output measurement. Ejection fraction is determined using an
exponential technique by synchronizing sensed R-waves with points of temperature changes
on the time-temperature curve. Once ejection fraction, cardiac output, and heart rate are
known, right ventricular volumes may be calculated. The measurement requires a
Baxter-Edwards fast response thermistor catheter and an ECG module to synchronize R-wave
detection to the time-temperature curves.
1.2.2 SvO
2
measurement
The COPSv module measures SvO
2
when coupled with a Baxter-Edwards OM-2E optical
module and a Swan-Ganz oximetry catheter. To measure SvO
2
, the system utilizes a
spectrophotometric technique involving the use of light emitting diodes (LEDs) that produce red
(660 nm) and infrared (810 nm) light. The light is transmitted to the blood through a single
plastic optical fiber in the oximetry catheter and reflected back through a separate optical fiber
to a photodetector in the optical module. The light is electrically transmitted to the COPSv
module and analyzed to determine SvO
2
.
The oximetry portion of the system measures SvO
2
in the pulmonary artery by detecting color
changes in the red blood cells. When pulses of red and infrared light are transmitted through
the oximetry catheter, the light is reflected from the red blood cells and transmitted back
through the catheter to the optical module. The amount of light reflected at each wavelength
depends primarily on the color of the blood and the number of red blood cells. Since the
number of red blood cells in the blood affects the amount of reflected light, the differences are
compensated for when the patient’s total hemoglobin value is entered. The optical module
stores and transfers SvO
2
calibration data. SvO
2
values can be affected by the presence of
methemeglobin or carboxyhemoglobin which imitate the absorption characteristics of HbO
2
.
Large concentrations of methemoglobin or carboxyhemoglobin could then cause a falsely
elevated SvO
2
. In cases where dysfunctional hemoglobins are suspected, SvO
2
should be
interpreted with caution.
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