What is a Pulse Oximeter Sensor?


Originally developed by Japanese engineers Michio Kishi and Takuo Aoyagi, pulse oximeter sensors are small non-invasive devices that are attached to a person's finger, or other appendages, to measure blood oxygen saturation (SpO2) and heart rate. These sensors determine how efficiently oxygen is being carried through the body by the bloodstream. There are different variations of pulse oximeter sensors that attach to fingers, ears or toes and, in the case of veterinary applications, on the tongue.

How does a pulse oximeter sensor work?

Pulse oximeter sensors work by use of a light-emitting diode and receptor to measure blood oxygen saturation. Oxygen saturation is the percentage of oxygen attached to the hemoglobin in the blood. The determining principle works based on the fact that oxygenated blood takes in more infrared light while deoxygenated blood takes in more red light. The pulse oximeter calculates the absorption of various wavelengths of light and will display the pulse rate and the amount of oxygen in the blood as a percentage.

What is a normal blood oxygen saturation level?

Most people sit at above 95% blood oxygen saturation. Diseases such as COPD, or other lung-compromising ailments or injuries, can cause blood oxygen saturation levels to drop below 90%. When oxygen levels in the blood drop below 90% the person is at risk of developing hypoxia, which means there is an abnormally low amount of oxygen in the blood.

What are the symptoms of hypoxia?

If you don't have a pulse oximeter sensor available, some of the symptoms of people who have abnormally low levels of oxygen in the blood are:


Known as shortness of breath, usually described as a struggle to breathe, tightening in the chest or breathlessness.


When there is low oxygen in the blood the body will attempt to fix it by breathing abnormally fast, often shallow, breaths.

Skin color changes:

When the blood has low levels of oxygen for a prolonged period, skin color can start to change to a blueish or purple color.

Fast heart rate:

The heart is very sensitive to oxygen levels and your heart rate will increase in order to supply more oxygen to the brain.

Brain hypoxia:

This is a more severe symptom that occurs when the brain is not getting enough oxygen to function correctly. Often times this symptom will involve confusion and poor judgment.

What is a normal heart rate?

Heart rate is the number of contractions, known as beats the heart makes per minute. A normal heart rate usually falls between 50 to 100 contractions per minute. During exercise or strenuous activities, the heart can beat faster in order to supply more blood to the body. Often times, professional athletes have a lower resting heart rate, sometimes as low as 30 beats per minute. Pulse oximeter sensors can be an excellent way to quickly and accurately check your heart rate, especially for people who have certain heart conditions.

Which type of pulse oximeter sensor is right for me?

Most patients will rely on a personal digital finger pulse oximeter for home use, these sensors are usually only designed to be used for short periods of time.

Digital Finger Pulse Oximeter

An all in one option designed for quick and easy spot-checking.

Some patients might require a pulse oximeter designed for continuous monitoring, such as a handheld or tabletop oximeter. Both of these will usually have more accurate results. These types of pulse oximeters are usually used by hospitals and attach to external sensors such as:

Disposable Sensors

Designed for maximum comfort and to be thrown away after single patient use.

Finger Clip Sensors

A standard clip-style sensor worn on the finger.

Soft Sensors

A silicone soft finger sensor designed for extra comfort.

Ear Clip or Lingual Sensors

These are designed to clip on the ear or, on the tongue, in veterinary surgical procedures.

Consult with your doctor to determine what is right for you.

How do you use a finger pulse oximeter or a finger clip sensor?

1) Spread open the sensor clasping mechanism by squeezing the rear tabs of the sensor together.

2) Place an index finger over the sensor window with the fingertip against the stop.

Note: If you are unable to position your finger correctly or your index finger is not available, a smaller finger can be used. In some cases, if your fingernail is long, the nail tip can extend over the finger stop.

3) Turn on the oximeter, wait for it to perform a measurement and record the reading.

Other things to keep in mind when using a pulse oximeter sensor

  • Using the sensor in the presence of direct high ambient light may result in inaccurate measurements. To get a correct reading you might need to shield the sensor with a surgical towel or dark cloth.
  • Nail polish or artificial nails may lead to inaccurate SpO2 measurements.
  • The performance of the sensor is compromised by motion.
  • When selecting a sensor site, priority should be given to an extremity free of an arterial catheter, blood pressure cuff, or intravascular infusion line.
  • If the sensor does not track the pulse reliably, the finger may be too thick, thin, or deeply pigmented to permit appropriate light transmission. If any of these situations occur, reposition the sensor or choose a different sensor.