6 Most Common Causes Of Errors In Pulse Oximeter Readings

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A pulse oximeter like the Nellcor pulse oximeter sensor is used to check the oxygen saturation level in our body. The reading serves as one of the many bases to monitor a variety of health conditions — including heart and lung disease, pneumonia, and COVID-19. The lower the reading is, it means that the person being monitored is finding it difficult to breathe.

How Does It Work

The pulse oximeter is a medical device clipped to a fingertip to measure the oxygen saturation levels in the arterial blood of an individual. It does this by shining a light through the finger, artery, and capillary beds. The light is then absorbed by haemoglobin in the blood. The less light absorbed the higher the oxygen saturation level in the blood. The pulse oximeter will also measure your heart rate.

An ideal pulse oximeter reading is between 96% to 99%. But while pulse oximetry is generally accurate (especially if you use trusted products like the Nellcor DS100a), there can still be errors in its readings.

Causes Of Reading Errors

When you use oximeters like Nellcor pulse oximeter sensor, their results typically ...
... fall within a 2% plus or minus range. This means that if the reading indicates a 96% oxygen saturation level, the real statistics may fall between 94% and 98%.

In some cases, the fluctuations can be beyond that 2%. These inaccuracies can be attributed to the following:

Pulse volume. There could be several reasons why a pulse is weak — including hypovolemic shock, low cardiac output, or certain health conditions such as arryhtmia. In these cases, the oximeter will find it hard to detect a signal, leading to an erroneous reading.

Skin temperature and thickness. The skin of the patient being monitored can also be a factor for oximeter reading errors. For instance, if the patient is very cold, the low skin temperature can hinder the device from detecting a signal. If the skin is too thick, it can also affect the performance of the device and cause fluctuations in the final reading of the oximeter.

Skin pigmentation. Did you know that having a darker skin pigmentation can also prevent having an accurate oximeter reading? As mentioned earlier, this medical device heavily uses light. If the skin has a dark pigmentation — or if there's any other obstruction like a fingernail polish — then, it won't be able to determine the oxygen saturation level of the patient properly.

Presence of bright lights. When using an oximeter, manufacturers advise users to shield the probe from direct light as it can affect the reading of the device. This light can be natural sunlight or light coming from an artificial source (e.g. Operating theatre light).

Shivering. The finger of the patient must be stable for an oximeter to produce a proper reading. If your finger is shivering, the movement will make it hard for the device to pick up a signal.

Carbon monoxide poisoning. Carbon monoxide binds with haemoglobin and displaces oxygen. If carbon monoxide enters the body (e.g., the patient got to inhale smoke from a fire) and a pulse oximeter is used on them, the reading is highly likely wrong.