20
5.3 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:
•
Incorrect sensor application or use;
•
High-frequency electrical noise, such as noise from electrosurgical apparatus
connected to the system;
•
Significant levels of dysfunctional haemoglobins (e.g. carboxyhaemoglobin
or methemoglobin);
•
Significant concentrations of dysfunctional haemoglobin, such as
carboxyhaemoglobin and methemoglobin;
•
Intravascular dyes such as indocyanine green or methylene blue;
•
Intense illumination, such as surgical lamps (especially ones with a xenon light
source), bilirubin lamps, fluorescent lights, infrared heating lamps, or direct
sunlight (exposure to intense illumination can be corrected by covering the
sensor with a dark material);
•
Excessive patient motion;
•
Venous pulsations;
•
SPO2 Is too low;
•
Improper sensor installation or incorrect contact position of the patient;
•
Placement of a sensor on the same extremity with a blood pressure cuff, arterial
catheter, or intravascular line.
•
Loss of pulse signal can occur in the following situation:
•
The sensor is too tight;
•
There is excessive illumination from light sources such as a surgical lamp, a
bilirubin lamp, or sunlight;
•
A blood pressure cuff is inflated on the same extremity as the one with a
SPO2 sensor attached;
•
The patient has hypotension, severe vasoconstriction, severe anaemia, or
hypothermia;
•
There is arterial occlusion proximal to the sensor;
•
The patient is in cardiac arrest or in shock.