Fluke Biomedical 2MF Index - Manual (Page 20)

Index 2MF
Users Guide
2-2
dioxide (CO2), can be expressed as milliliters of gas per liter of blood, and can be
indicated by the partial pressure that the gases exert in your blood at a given temperature.
Pulse Oximeters
Because of their ease of use in many hospital- and critical-care situations, pulse oximeters
have greatly increased in popularity since their introduction. Today, pulse oximeters are
virtually required equipment in situations where the monitoring of arterial oxygen
saturation (SaO2) is essential, such as when anesthesia is in use, both during an operation
and in post-operative recovery, intensive care, transport, and patient home care.
Pulse oximeters have proven to be capable and reliable, being highly accurate in
measuring blood SaO2 in the range of 80-100%, while at the same time needing little, if
any, calibration. No patient preparation is required before using the pulse oximeter; in
addition, the devices are so simple to operate that specialized training is unnecessary.
How Pulse Oximeters Work
Pulse oximeters are defined as non-invasive, arterial, oxygen-saturation monitors which
measure the ratio of two principal forms of hemoglobin in the blood: saturated arterial
hemoglobin (also called oxyhemoglobin), HbO2/SAT, to unsaturated (or reduced)
hemoglobin, Hb.
The arterial oxygen saturation, SaO2, is defined as the ratio of the concentration of
oxyhemoglobin (cHbO2) to the concentration of HbO2 + Hb (cHbO2 + cHb). Oxygen
saturation is commonly expressed as a percentage and is calculated according to the
formula in Figure 2-2.
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Figure 2-2. Formula for Determining Saturated Oxygen Level
Using this information, a correctly calibrated and operating pulse oximeter can accurately
predict the level of oxygen in the blood, which in turn provides valuable data about the
health of a patient, and in the case of anesthesia and post-operative recovery, the status of
the patient.
Spectrophotometry
Pulse oximeters operate on the principle known as spectrophotometry, using wavelengths
of light to determine the concentration of oxygen in the blood. Because we already know
the wavelengths for the light absorption of blood hemoglobin, we can mathematically
determine the arterial oxygen saturation in a patient's blood.
The light emitting diodes (LED's) of a pulse oximeters shine two types of light—near
infrared light (at 940 nanometers) and red light (at 660 nanometers)—wavelengths that
pass through the skin and which are absorbed by both the oxyhemoglobin and the
reduced hemoglobin. These light beams pass through the index finger of a patient to
photo detectors on the opposite side of the pulse oximeter.