GE CARESCAPE, User Manual

Page: 279 / 548

Mixed venous oxygen saturation (SvO₂)
SvO
2
measurement description
The SvO
2
value is measured continuously by spectrophotometry. The algorithm
consists of five different parts:
●
Initialization: When connected, a number of start-up procedures are performed
prior to normal operation. These procedures include transfer of calibration factors
and initialization of LED currents.
●
Calibration
●
Signal processing and SvO
2
calculation: Light of various wavelengths (red 660 nm
and infrared 810 nm) 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. The light is electrically transmitted and analyzed. From the
amount of reflected light it is possible to measure the amount of light absorbed
by hemoglobin and oxyhemoglobin, resulting in the SvO
2
value. The SvO
2
value
is displayed as a percentage.
●
Automatic gain control: The intensity of the red and infrared signals can be
amplified by four different gains. The gain is selected automatically to achieve
optimal signal levels.
●
Signal quality
SvO
2
troubleshooting
Problem Solution
SvO
2
levels are too high
●
Position the catheter correctly.
●
Calibrate in vivo.
In vivo calibration fails
●
Check the connections.
●
Check that the optical cables have no sharp bends.
●
If the in vivo calibration fails again, replace the catheter and/or the
optical module, and repeat the procedure.
2062971-001 CARESCAPE Modular Monitors 279