Automatic Calibration; Functional Versus Fractional Saturation - Nellcor OxiMax N-595 Operator's Manual

Principles of Operation

Automatic Calibration

Functional versus Fractional Saturation

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saturation of arterial hemoglobin, the monitor uses the pulsatile
nature of arterial flow. During systole, a new pulse of arterial blood
enters the vascular bed, and blood volume and light absorption
increase. During diastole, blood volume and light absorption reach
their lowest point. The pulse oximeter bases its SpO
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.
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 O
accurately measure SpO
During monitoring, the instrument's software selects coefficients that
are appropriate for the wavelength of that individual O
red LED; these coefficients are then used to determine SpO
Additionally, to compensate for differences in tissue thickness, the
light intensity of the O
This pulse oximeter measures functional saturation – oxygenated
hemoglobin expressed as a percentage of the hemoglobin that can
transport oxygen. It does not detect significant amounts of
dysfunctional hemoglobin, such as carboxyhemoglobin or
methemoglobin. In contrast, hemoximeters such as the IL482 report
fractional saturation – oxygenated hemoglobin expressed as a
percentage of all measured hemoglobin, including measured
dysfunctional hemoglobins. To compare functional saturation
measurements to those from an instrument that measures fractional
saturation, fractional measurements must be converted as follows:
functional saturation =
100 - (% carboxyhemoglobin + % methemoglobin )
M sensor's red LED to
XI AX
.
2
M sensor's LEDs is adjusted automatically.
XI AX
fractional saturation
measurements
2
M sensor's
XI AX
.
2
x100