11-20
11.4.4 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:
Incorrect sensor application or use;
Placement of a sensor on the same extremity with a blood pressure cuff, arterial catheter, or
intravascular line;
Exposure to excessive illumination, such as surgical lamps (especially ones with a xenon
light source), bilirubin lamps, fluorescent lights, infrared heating lamps, or direct sunlight
(exposure to excessive illumination can be corrected by covering the sensor with a dark
material);
Excessive patient motion;
Venous pulsations;
Intravascular dyes such as indocyanine green or methylene blue;
Defibrillation;
Other physiological conditions or medical procedures that may interfere with the monitor’s
measurements include significant levels of dysfunctional hemoglobin, low perfusion, and dark
pigment.
Loss of pulse signal can occur in the following situations:
The sensor is too tight;
A blood pressure cuff is inflated on the same extremity as the one with a SpO2 sensor
attached;
There is arterial occlusion proximal to the sensor.
Select an appropriate sensor, apply it as directed, and observe all warnings and cautions presented
in the directions for use accompanying the sensor. Clean and remove any substances such as nail
polish from the application site. Periodically check to ensure that the sensor remains properly
positioned on the patient.
If patient movement presents a problem, try one or more of the following remedies to correct the
problem.
Verify that the sensor is properly and securely applied.
Move the sensor to a less active site.
Use an adhesive sensor that tolerates some patient motion.
Use a new sensor with fresh adhesive backing.
If poor perfusion affects performance, consider using the Oxisensor R-15 sensor; it obtains
measurements from the nasal septal anterior ethmoid artery, an artery supplied by the internal
carotid. This sensor may obtain measurements when peripheral perfusion is relatively poor. For
low peripheral perfusion, consider using the Nellcor RS-10 sensor, which is applied to the
forehead or temple. These are sites that may be spared during peripheral vasoconstriction.
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