Sources of Errors in Pulse Oximeter Readings

Pulse oximetry is just one of the many commonly used monitoring devices in patient care. But this doesn’t spare each device from errors which may be caused by technical problems, or poor understanding of its principles and limitations.

Falsely Low Readings

There are many possible sources of error in pulse oximetry readings. A falsely low result may be due to the following factors:

1.) Poor peripheral arterial perfusion and low blood pressure (hypotension)

The device is intended to calculate variations in light absorbance produced by pulsatile blood. In this way, changes in light absorbance because of the skin and surrounding tissues are eliminated. Any factor that decreases arterial perfusion or vascular pulsations may greatly reduce the capacity of the pulse oximeter to identify and evaluate the light transmissions, hence, inaccuracy of measuring the arterial oxygen saturation. One good example is vaso-occlusive crisis of sickle cell anemia. Physical factors may also include getting a blood pressure reading on the same arm where the fingertip pulse oximeter is attached.

2.) Methemoglobinemia

Considerable levels of methemoglobin could cause readings to fall below towards 85%.

3.) Intravenous dyes

In medicine, a dye called methylene blue, which also used to treat methemoglobinemia, indigocarmine, and indocyanine green may cause momentary disruption in the oximetry readings up to 65%.

4.) Opaque nail polish

Opaque nail polish and synthetic fingernails may cause an interference with the absorption of light.

5.) High intensity light sources

While the instrument is being used, avoid exposure of the probe and the measuring site to intense bright light as this may lower the spot checks.

Falsely High Readings

1.) Carbon monoxide poisoning

Carbon monoxide has a higher affinity to hemoglobin compared to oxygen. When it binds to hemoglobin, it produces carboxyhemoglobin which is inefficient in delivering oxygen to various tissues. Carboxyhemoglobin absorbs much light as oxygen and registers a falsely high oxygen saturation.

Other Error Sources

In some cases, motion can cause considerable changes in the pulse oximeter readings. Nowadays, pulse oximeters can already read through motion that reduces the interference caused by exaggerated movements.