MEDRAD
Veris
8600
7 —2
The light from the LEDs shines into a pulsating vascular bed. A
photodetector located opposite or alongside the LEDs measures the
intensity of each wavelength transmitted through the monitoring site.
The light intensity is converted to an electrical signal, which is input to
the monitor. The effects of skin pigmentation, venous blood, and
other tissue constituents are eliminated by separating out the
pulsating absorption data.
SpO
2
Clinical Testing
and Accuracy
All MEDRAD oximeters (DOX™ compatible) have SpO
2
calibration
tables which were originally generated by monitoring desaturated
human patients or volunteers and matching their displayed SpO
2
value to the value determined by sampling arterial blood and
measuring functional SaO
2
with a clinical laboratory grade multi
wavelength optical oximeter (i.e. CO-oximeter). The final SpO
2
calibration curve was then generated based upon numerous patients'
data over the range of 40 to 99% SaO
2
. All accepted data were taken
from patients with dyshemoglobin (i.e., carboxyhemoglobin,
methemoglobin) concentrations near zero.
This oximeter is a two-wavelength device, which is calibrated to
measure functional SpO
2
only when dyshemoglobin concentrations
are near zero. The accuracy specifications of this device will not be
met with high concentrations of dyshemoglobins. Significant
concentrations of carboxyhemoglobin results in a higher displayed
SpO
2
value than is actually present in the patient.
Special MR-compatible sensors help provide for patient safety in the
MR environment because the sensor cable is made of a material that
does not conduct electricity even if the cable is looped within the MR
scanner. For the same reason, the sensor and cable are immune to
electromagnetic interference, such as might be produced by high
frequency (HF) surgical equipment. Each MR-compatible sensor
uses a fiber optic light guide to carry light from the light sources to the
patient. A separate light guide brings light, which has passed through
the patient, to the light detector. The light sources and detector are
located in the connector housing of the fiber optic sensor.
Gating Signals
The input gating signal is derived from any one of two sources—ECG
or Plethysmogram (SpO
2
) waveform and is available in 2 user-
selectable forms, pulse or waveform. An icon of the gating signal
source and a visual indication appears at the upper left corner of the
heart rate numerical display box.
S
P
O
2
GATING
SpO
2
gating is dependent upon the patient's peripheral perfusion at
the location where the sensor is placed. The pulse oximeter sensor is
placed on the selected location of the patient. The signal generated
from the patient's pulse is transmitted through fiber optic cables to the
transducer portion of the SpO
2
cable where it is converted to an
electrical signal. The electrical signal is sent to the Veris monitor and
then to the scanner which may be used to trigger the sequence.
