If you have shortness of breath or a lung or heart condition, your doctor may recommend using a pulse oximeter. If you’ve never used one of these devices before, you may be wondering what they are and how they work.
What is Pulse Oximetry?
Pulse oximetry is a non-invasive test that measures your body’s oxygen saturation level, or your blood oxygen level. Oximeters can detect even the slightest changes in how efficiently oxygen is carried to your legs and arms – the extremities that are farthest from the heart.
The small device features a clip-like design and attaches to a body part, typically a finger.
In most cases, pulse oximeters are used in hospitals and emergency rooms, but pulmonologists may also have them in their offices.
Today, you can purchase at-home pulse oximeters that allow you to check your oxygen levels at home. Those with heart or lung conditions can benefit from being able to check their oxygen levels.
Uses for a Pulse Oximeter
Why would you need to use a pulse oximeter? The primary purpose of the device is to see how well the heart is pumping oxygen throughout the body.
These devices may be used on people with the following conditions:
- Congenital heart defects
- Lung cancer
- COPD (chronic obstructive pulmonary disease)
- Heart attack or heart failure
Knowing a person’s blood oxygen levels can be useful in a number of scenarios, aside from emergency situations. A pulse oximeter may be used to:
- Check your ability to tolerate physical activity
- See how well a lung medication is working
- Check for sleep apnea
- Determine how effective a ventilator is
- Monitor oxygen levels during surgical procedures
- Determine the effectiveness of supplemental oxygen therapy
- Determine if you need help breathing
How Pulse Oximeters Work
Pulse oximeters have a small finger probe and use a cold light source that shines light through the tip of the finger. The light makes the fingertip appear to be red.
The device analyzes the light that passes through the finger and determines the percentage of oxygen in the red blood cell.
It’s important to keep in mind that the device measures oxygen levels without having to use needles or take a blood sample.
Sometimes, the clip is placed on the earlobe or the toe. Regardless of whether the probe is placed on the finger or another part of the body, the test itself is painless. You may feel some pressure when the clip is attached, but there should be no pain.
If the test is performed on your finger, your doctor may ask you to remove your fingernail polish, as it can interfere with the test.
The probe will remain attached to your body until a full reading has been performed. If the reading is part of a stress test (determining your tolerance for physical activities), you will wear the probe during both the exercise and recovery phases. If used during surgery, the probe will be attached before the procedure and removed once you are awake and no longer being supervised.
Interpreting the Readings
Pulse oximeters will display your blood oxygen level on the device itself. The number helps your doctors and nurses determine which type of treatment – if necessary – is needed. You may need supplemental oxygen.
These devices provide accurate results, even when using at-home devices. Results are usually accurate within two percentage points. Factors, such as temperature and movement, can affect your oxygen levels.
A normal pulse oximeter reading will range from 95% to 100%. If your reading is below 90%, this would be considered low.
Factors that Can Affect Reading Accuracy
There are several factors that can affect the accuracy of readings.
- External influences: Pulse oximeters measure the amount of light transmitted through the arterial blood. Bright light shining on the sensor may impact the readings. Other external influences include nail polish, dried blood and dirty sensors. Seizures, shivering, moving the sensor and optical shunting can also affect readings.
- Patient condition: Certain medical conditions and patients in frail conditions may affect the readings.
- False high readings: Pulse oximeters may also give a falsely high reading if carbon monoxide is present. Carbon monoxide binds to hemoglobin at a rate 250 times stronger than oxygen and turns the hemoglobin red. Pulse oximeters are unable to distinguish between oxygen-saturated hemoglobin molecules and those saturated in carbon monoxide. False high readings are common with cigarette smokers. Readings can be affected for up to four hours after smoking a cigarette.
While pulse oximeters have limitations, they still provide an accurate look at your oxygen levels and offer a window into your overall health. This information can be used to make treatment decisions.
There are no known risks of using a pulse oximeter.
What Can Cause Low Blood Oxygen Levels?
There are several factors that can cause your blood oxygen levels to be lower than normal. It helps to understand which factors are needed to supply cells and tissues with oxygen.
- First, there must be oxygen in the air that you are breathing.
- The lungs must be able to inhale the oxygen in the air and exhale carbon dioxide.
- The bloodstream must be able to circulate blood to the lungs and take up the oxygen to carry throughout the body.
If any of these factors are altered in any way, it can lead to low oxygen levels. It could be asthma, high altitude, heart disease or something else that lowers oxygen levels.
When blood oxygen levels fall below normal levels, you may experience headache, shortness of breath, restlessness and confusion.
Common causes of low blood oxygen, or hypoxemia, include:
- Congenital heart defects
- Congenital heart disease
- Acute respiratory distress syndrome
- Sleep apnea
- Pulmonary edema
- Pulmonary fibrosis
- Pulmonary embolism
- Interstitial lung disease
- Certain medications
If a pulse oximeter indicates that you have low blood oxygen, doctors will determine the root cause of the problem and find a treatment plan to bring oxygen levels back to normal. In most cases, supplemental oxygen will bring levels to normal. Lifestyle changes may be prescribed to keep levels at the normal range.