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ViSi Tip - Ambient Light


Pulse oximetry is typically used to measure various blood flow characteristics including, but not limited to, the blood-oxygen saturation of hemoglobin in arterial blood, the rate of blood pulsations corresponding to each heartbeat of a patient, and the volume of individual blood pulsations supplying the tissue. The measurement of these characteristics has been accomplished by the use of non-invasive sensors that scatter light through a portion of the patient's tissue where blood perfuses the tissue, and photoelectrically senses the absorption of light in such tissue. The amount of light absorbed is then used to calculate the amount of blood constituent being measured.

For measuring blood oxygen level, such sensors have typically been provided with a light source that is adapted to generate light of at least two different wavelengths, and with photodetectors sensitive to both of those wavelengths, in accordance with known techniques for measuring blood oxygen saturation. Known non-invasive sensors include devices that are secured to a portion of the body, such as a finger, an ear, or the scalp. The tissue of these body portions is perfused with blood and the tissue surface is readily accessible to the sensor.

One problem with oximeter measurements is that in addition to receiving the light that was directed at the tissue, ambient light is also detected by the photodetector. Oxygen saturation measurements using SpO2 are dependent on proper sensor placement, exposure to ambient light conditions, and general patient conditions. Before making clinical decisions based on SpO2 measurements, verify the measurement using another clinically acceptable method, such as arterial blood gas analysis. 

High ambient light conditions, including direct sunlight, may interfere with the performance of the ViSi Mobile Thumb Sensor. Ambient light occurs when an external light interferes with the optical sensor of a pulse oximeter. To prevent this from occurring with the ViSi Mobile thumb sensor:

  • Ensure that the thumb sensor is completely covered by the thumb tape with edges smoothed down to the skin.
  • Minimize overhead lights and direct sunlight shining onto sensors from the windows in the room.
  • Wrapping Coban over thumb tape can help block light
  • Ensure that the thumb tape covers the entire sensor when wrapping, the sensor should not be visible
  • Use the thumb tape over the thumb posey whenever possible for the best shielding of light.

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Filed Under: Remote Patient Monitoring, Nurses, Healthcare, ViSi Mobile, ViSi Tip of the Month