Technical Discussion
Measured versus Calculated Saturation
SatSeconds Alarm Management
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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 =
When saturation is calculated from a blood gas partial pressure of oxygen (PO
the calculated value may differ from the SpO
This usually occurs because the calculated saturation was not appropriately
corrected for the effects of variables that shift the relationship between PO
pH, temperature, the partial pressure of carbon dioxide (PCO
fetal hemoglobin. See Figure 25.
Figure 25: Oxyhemoglobin Dissociation Curve
The NPB-40 utilizes Nellcor SatSeconds alarm management technique.
SatSeconds is a function of the software within the NPB-40. With the SatSeconds
technique, upper and lower alarm limits are set in the same way as traditional
alarm management. The clinician also sets a SatSeconds limit that allows
monitoring of %SpO
below the selected lower alarm limit for a period of time
2
before an audible alarm sounds. Refer to the NPB-40 Operator's manual for
managing SatSeconds.
fractional saturation
100 - (% carboxyhemoglobin + % methemoglobin )
measurement of a pulse oximeter.
2
x100
),
2
and
2
), 2,3-DPG, and
2