11-6
11.2.4 Measurement Limitations
If the accuracy of any measurement does not seem reasonable, first check the patient’s vital signs
by an alternate method. Then check the instrument for proper function. Inaccurate measurements
may be caused by:
Improper SpO2 sensor;
High-frequency electrical noise, including noise created by the host system, or noise from
external sources, such as electrosurgical apparatus connected to the system;
Oximeters and oximetry sensors used during magnetic resonance imaging (MRI) scanning.
Induced current could potentially cause burns;
Intravascular dye injections;
Excessive patient motion;
Excessive ambient light;
Improper sensor installation or incorrect sensor placement on the patient
Sensor temperature (optimal temperature is between 28℃ and 40℃);
The sensor is placed on a limb that is attached to a blood pressure cuff, arterial catheter, or
intravascular line;
Concentration of dysfunctional hemoglobin, such as carboxyhemoglobin and
methemoglobin;
SpO2 too low;
Low circular perfusion of the applied part;
Shock, anemia, low temperature and application of vasomotor all reduce the arterial blood
flow and may affect the pulse oximetry measurement.
The absorption of oxyhemoglobin (HbO
2
) and deoxyhemoglobin to the light of special
wavelength may also affect SpO
2
measurement. If there exist other substances (like carbon
hemoglobin, methemoglobin, methylene blue and indigo carmine) absorbing the light of the same
wavelength, they may result in false or low SpO
2
reading.
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