What is a Pulse Oximeter?

By [email protected] | January 15, 2021

A pulse oximeter (pulse ox) is a noninvasive device that estimates the amount of oxygen in your blood. It does so by sending infrared light into capillaries in your finger, toe, or earlobe. Then it measures how much light is reflected off the gases.

A reading indicates what percentage of your blood is saturated, known as the SpO2 level. This test has a 2 percent error window. That means the reading may be as much as 2 percent higher or lower than your actual blood oxygen level.

This test may be slightly less accurate, but it’s very easy for doctors to perform. So doctors rely on it for fast readings.

Things like dark nail polish or cold extremities can cause the pulse ox to read lower than normal. Your doctor may remove any polish from your nails before using the machine or if your reading seems abnormally low.

Because a pulse oximeter is noninvasive, you can perform this test yourself. You can purchase pulse ox devices on our online store. Talk to your doctor before using a home device so that you understand how to interpret the results.

Where your blood oxygen level should fall
A measurement of your blood oxygen is called your oxygen saturation level. In medical shorthand, you may hear it called a PaO2 when using a blood gas and an O2 sat (SpO2) when using a pulse ox. These guidelines will help you understand what your result might mean:

Normal: A normal ABG oxygen level for healthy lungs falls between 80 and 100 millimeters of mercury (mm Hg). If a pulse ox measured your blood oxygen level (SpO2), a normal reading is typically between 95 and 100 percent.

Below normal: A below-normal blood oxygen level is called hypoxemia. Hypoxemia is often cause for concern. The lower the oxygen level, the more severe the hypoxemia. This can lead to complications in body tissue and organs.

Your doctor can provide recommendations as to what ranges of oxygen levels are acceptable for you.

Normally, a pulse ox (SpO2) below 95 percent is considered low. If your reading drops below 95 percent, immediately inform your doctor to advise on next steps in the present Covid-19 scenarios.

Above normal: If your breathing is unassisted, it’s difficult for your oxygen levels to be too high. In most cases, high oxygen levels occur in people who use supplemental oxygen. This can be detected on an ABG.

What happens if your oxygen level is too low
When your blood oxygen level goes outside the typical range, you may begin experiencing symptoms.

This includes:

  • shortness of breath
  • chest pain
  • confusion
  • headache
  • rapid heartbeat

If you continue to have low blood oxygen levels, you may show symptoms of cyanosis. The hallmark sign of this condition is a blue discoloration of your nail beds, skin, and mucus membranes.

Cyanosis is considered an emergency. If you’re experiencing symptoms, you should seek immediate medical attention. Cyanosis can lead to respiratory failure, which can be life-threatening.

How to adjust your blood oxygen level
If your blood oxygen level is too low, you may need to boost your oxygen saturation. This is often done with supplemental oxygen.

Home supplemental oxygen is considered a medication, and your doctor must prescribe it. It’s important to follow your doctor’s specific advice on how home oxygen should be used to avoid complications. Your health insurance / medical aid may cover the expense.

What causes blood oxygen levels to be low?

Conditions that can negatively affect your blood oxygen level include:

  • Covid-19, including chronic bronchitis and emphysema
  • acute respiratory distress syndrome
  • asthma
  • collapsed lung
  • anemia
  • congenital heart defects
  • heart disease
  • pulmonary embolism

These conditions may prevent your lungs from adequately inhaling oxygen-containing air and exhaling carbon dioxide. Likewise, blood disorders and problems with your circulatory system may prevent your blood from picking up oxygen and transporting it throughout your body.

Any of these problems or disorders can lead to declining oxygen saturation levels. As your oxygen levels fall, you may begin experiencing symptoms of hypoxemia.

People who smoke may have an inaccurately high pulse ox reading. Smoking causes carbon monoxide to build up in your blood. A pulse ox can’t tell the difference between this other type of gas and oxygen.

If you smoke and need to know your blood oxygen level, an ABG may be the only way to receive an accurate reading.

The bottom line
Most people don’t need to regularly monitor their blood oxygen level. Only people with health problems that cause low oxygen states are usually asked to check their levels. Even then, the less invasive pulse oximetry method is often as useful as an invasive ABG.

Although it does have a margin of error, a pulse ox reading is usually accurate enough. If your doctor requires a more precise measurement, they can follow up with an ABG test.

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