Nellcor Oximax NPB-40, Service Manual

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Technical Discussion
76
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:
Measured versus Calculated Saturation
When saturation is calculated from a blood gas partial pressure of oxygen (PO
2
),
the calculated value may differ from the SpO
2
measurement of a pulse oximeter.
This usually occurs because the calculated saturation was not appropriately
corrected for the effects of variables that shift the relationship between PO
2
and
pH, temperature, the partial pressure of carbon dioxide (PCO
2
), 2,3 - DPG, and
fetal hemoglobin. See Figure 25.
Figure 25: Oxyhemoglobin Dissociation Curve
SatSeconds Alarm Management
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
2
below the selected lower alarm limit for a period of time
before an audible alarm sounds. Refer to the NPB-40 Operator's manual for
managing
SatSeconds .
functional saturation =
fractional saturation
100 - (% carboxyhemoglobin + % methemoglobin )
x100