Rad-67
Chapter 1: Technology Overview
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23
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Pulse CO-Oximetry vs. Drawn Whole Blood Measurements
When SpO
2
and SpHb measurements obtained from the Rad-67 (noninvasive) are compared
to drawn whole blood (invasive) measurements by blood gas and/or laboratory CO-Oximetry
methods, caution should be taken when evaluating and interpreting the results.
The blood gas and/or laboratory CO-Oximetry measurements may differ from the SpO
2
and
SpHb measurements of the Rad-67. Any comparisons should be simultaneous, meaning the
measurement on the device should be noted at the exact time that blood is drawn.
In the case of SpO
2
, different results are usually obtained from the arterial blood gas sample
if the calculated measurement is not appropriately corrected for the effects of variables that
shift the relationship between the partial pressure of oxygen (pO
2
) and saturation, such as:
pH,temperature, the partial pressure of carbon dioxide (pCO
2
), 2,3-DPG, and fetal
hemoglobin.
In the case of SpHb, variation in hemoglobin measurements may be profound and may be
affected by sampling technique as well as the patient's physiological conditions. Any results
exhibiting inconsistency with the patient's clinical status should be repeated and/or
supplemented with additional test data. As with most hemoglobin tests, a laboratory blood
sample should be analyzed prior to clinical decision making.
High levels of bilirubin may cause erroneous SpO
2
and SpHb readings. As blood samples are
usually taken over a period of 20 seconds (the time it takes to draw the blood) a meaningful
comparison can only be achieved if the oxygen saturation (SaO
2
), levels of
carboxyhemoglobin (COHb), and MetHb of the patient are stable and not changing over the
period of time that the blood gas sample is taken. Subsequently, blood gas and laboratory
CO-Oximetry measurements of SpO
2
and SpHb may vary with the rapid administration of
fluids and in procedures such as dialysis. Additionally, drawn whole blood testing can be
affected by sample handling methods and time elapsed between blood draw and sample
testing.
Measurements with Low Signal IQ should not be compared to laboratory measurements.
General Description for Total Hemoglobin (SpHb)
Pulse CO-Oximetry is a continuous and noninvasive method of measuring the levels of total
hemoglobin (SpHb) in arterial blood. It relies on the same principles of pulse oximetry to
make its SpHb measurement.
Successful Monitoring for SpHb
A stable SpHb reading is associated with correct sensor placement, small physiological
changes during the measurement and acceptable levels of arterial perfusion at the
measurement site. Physiological changes at the measurement site are mainly caused by
fluctuations in the oxygen saturation, blood concentration and perfusion. See
Safety
Information, Warnings and Cautions
on page 11 and
Troubleshooting Measurements
on
page 67.
General Description for Total Arterial Oxygen Content (CaO2)
Oxygen (O
2
) is carried in the blood in two forms, either dissolved in plasma or combined
with hemoglobin. The amount of oxygen in the arterial blood is termed the oxygen content
