Datex-Ohmeda S/5 M-ESTPR, Technical Reference Manual Slot

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Datex-Ohmeda S/5 monitors
Document No. 800 1008-2
8
A general limitation of the above pulse oximetry principle is that due to only two wavelengths used
only two hemoglobin species can be discriminated by the measurement.
The modern pulse oximeters are empirically calibrated either against fractional saturation
SaO
2
frac;
bin Dyshemoglo Hb HbO
HbO
frac SaO
2
2
2
+ +
=
Formula 1
or against functional saturation SaO
2
func;
Hb HbO
HbO
func SaO
2
2
2
+
=
Formula 2
which is more insensitive to changes of carboxyhemoglobin and methemoglobin concentrations in
blood.
The oxygen saturation percentage SpO
2
measured by Datex-Ohmeda module is calibrated against
the functional saturation SaO
2
func. The advantage of this method is that the accuracy of SpO
2
measurement relative to SaO
2
func can be maintained even at rather high concentrations of
carboxyhemoglobin in blood. Independent of the calibration method, pulse oximeter is not able to
correctly measure oxygen content of the arterial blood at elevated carboxyhemoglobin or
methemoglobin levels.
Plethysmographic pulse wave
The plethysmographic waveform is derived from the IR signal and reflects the blood pulsation at
the measuring site. Thus the amplitude of the waveform represents the perfusion.
Pulse rate
The pulse rate calculation is done by peak detection of the plethysmographic pulse wave. The
signals are filtered to reduce noise and checked to separate artifacts.
Probe
The standard probe is a finger clamp probe which contains the light source LEDs in one half and
the photodiode detector in the other half. Different kinds of probes are available from Datex-
Ohmeda.