Nellcor OXIMAX N-560, Operator'S Manual

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Principles of Operation
92
SpO
2
measurements on the difference between maximum and minimum
absorption (measurements at systole and diastole). By doing so, it focuses
on light absorption by pulsatile arterial blood, eliminating the effects of
nonpulsatile absorbers such as tissue, bone, and venous blood.
There are various matrixes within the O
XI
M
AX
algorithm. Some are used
to assess the severity of conditions presented to the N - 560 in measuring
SpO
2
and pulse rate. These individual matrixes or combinations of these
matrixes are used to drive the LED indicators on the N - 560 front panel.
During challenging measurement conditions, which could be caused by
low perfusion, interference, external interference, like ambient light, or a
combination of these, the
O
XI
M
AX
algorithm automatically extends the
amount of data required for measuring SpO
2
and pulse rate, depending on
the measurement conditions. During normal measurement conditions in
the Normal response mode, the averaging time is 6 to 7 seconds. If the
resulting dynamic averaging time exceeds 20 seconds, the
Pulse Search
indicator is continuously illuminated and SpO
2
and pulse rate is updated
every second. As measurement conditions become even more
challenging, the amount of data required continues to extend. If the
dynamic averaging time reaches 40 seconds, the
Pulse Search
indicator
begins flashing and the SpO
2
and pulse rate display flashes zeros
indicating a loss - of - pulse condition.
Automatic Calibration
Because light absorption by hemoglobin is wavelength dependent and
because the mean wavelength of LEDs varies, an oximeter must know the
mean wavelength of the sensor's red LED to accurately measure SpO
2
.
During monitoring, the N-560's software selects coefficients that are
appropriate for the wavelength of that individual sensor's red LED; these
coefficients are then used to determine SpO
2
.
Additionally, to compensate for differences in tissue thickness, the light
intensity of the sensor's LEDs is adjusted automatically.