Chapter 2: Intended Use and Monitor Features
2-2
Clinician’s Operation Manual
Theory of Operation
The pulse oximeter determines %SpO
2
and pulse rate by passing two wavelengths of low
intensity light, one red and one infrared, through body tissue to a photodetector. Information
about wavelength range can be especially useful to clinicians. Wavelength information for this
device can be found in the
SpO
2
Specifications
section of this manual.
Pulse identification is accomplished by using plethysmographic techniques, and oxygen
saturation measurements are determined using spectrophotometric oximetry principles. During
measurement, the signal strength resulting from each light source depends on the color and
thickness of the body tissue, the sensor placement, the intensity of the light sources, and the
absorption of the arterial and venous blood (including the time varying effects of the pulse) in the
body tissues.
Figure 2-1: Theory of Operation
Low intensity Red and Infrared LED light sources
Detector
The oximeter processes these signals, separating the time invariant parameters (tissue thickness,
skin color, light intensity, and venous blood) from the time variant parameters (arterial volume
and SpO
2
) to identify the pulses and calculate functional oxygen saturation. Oxygen saturation
calculations can be performed because blood saturated with oxygen predictably absorbs less red
light than oxygen-depleted blood.
WARNING! Since measurement of SpO
2
depends on a pulsating vascular bed, any
condition that restricts blood flow, such as the use of a blood pressure cuff or
extremes in systemic vascular resistance, may cause an inability to determine
accurate SpO
2
and pulse rate readings.
WARNING! Under certain clinical conditions, pulse oximeters may display dashes if
unable to display SpO
2
and/or pulse rate values. Under these conditions, pulse
oximeters may also display erroneous values. These conditions include, but are
not limited to: patient motion, low perfusion, cardiac arrhythmias, high or low
pulse rates or a combination of the above conditions. Failure of the clinician to
recognize the effects of these conditions on pulse oximeter readings may result
in patient injury.
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