How to Use a Pulse Oximeter

A fingertip pulse oximeter is one of the simplest medical devices to operate: clip it on and read the display. Getting a trustworthy reading takes a little more care. Cold fingers, movement and nail polish can all distort the result. These steps will help you measure correctly and consistently.

What a pulse oximeter does

The FDA explains that a pulse oximeter is usually placed on a fingertip and uses light beams to estimate the oxygen saturation of the blood and the pulse rate. Oxygen saturation, shown as SpO2, is the percentage of the blood’s oxygen-carrying capacity that is in use. The device gives an estimate without a blood sample.

Before you begin

Pulse oximeters are most useful when a healthcare professional has asked you to monitor at home, for example with a lung or heart condition. Ask your doctor:

• how often to measure;
• what readings are expected for you;
• at what reading to call, and at what reading to seek urgent help.

Read the instructions supplied with your device. Our Fingertip Pulse Oximeter displays SpO2 and pulse rate and comes with batteries and a lanyard.

Step-by-step

1. Prepare your hand

• Remove nail polish and artificial nails from the finger you will use. MedlinePlus notes that dark nail polish can block the light from the oximeter.
• Warm your hand if it is cold. Rub your hands together or hold them in warm water, then dry them.
• Make sure the finger is clean and dry.

2. Rest

Sit down and rest quietly for about five minutes. Measuring straight after activity gives a different picture.

3. Position yourself

• Sit upright.
• Rest your hand on a table or on your chest at about heart level.
• Relax your hand.

4. Attach the oximeter

• Open the clip and slide a finger in fully, usually the index or middle finger, with the nail facing up toward the display unless your instructions say otherwise.
• The fingertip should reach the end of the device and cover the sensor.

5. Switch on and keep still

• Press the power button.
• Keep your hand still and breathe normally. Do not talk.
• Movement and shivering interfere with the signal.

6. Wait for a steady reading

The numbers will change at first. Wait until the reading has held steady for at least several seconds, and allow up to a minute if needed. Many devices show a pulse bar or waveform; a regular pattern suggests a good signal.

7. Read and record

Note:

• the date and time;
• the SpO2 percentage;
• the pulse rate;
• anything relevant, such as symptoms, activity or whether you were using oxygen.

8. Remove and switch off

Take the device off. Most switch off automatically.

Common causes of inaccurate readings

The FDA lists factors that can affect accuracy:

• poor circulation;
• skin pigmentation;
• skin thickness;
• skin temperature;
• current tobacco use;
• use of fingernail polish.

In addition, practical problems include:

• movement or shivering;
• a finger not fully inserted;
• bright light shining on the sensor;
• low batteries.

The FDA has also raised concerns that pulse oximeters may be less accurate in people with darker skin pigmentation. This is one reason to look at trends over time and never to rely on a single number.

If the reading seems wrong

1. Check that your hand is warm and still.
2. Reseat the oximeter or try another finger.
3. Rest and measure again after a few minutes.
4. Replace the batteries if the display is dim or a low-battery symbol shows.

If the reading stays low, or you feel unwell, follow your doctor’s instructions or seek medical advice. Do not keep re-measuring in the hope of a better number.

Making sense of the numbers

MedlinePlus states that a normal oxygen saturation level ranges between 95% and 100%, and that readings may be 2% to 4% higher or lower than the actual blood oxygen level. For adults, a normal resting pulse is 60 to 100 beats per minute. Your own target may differ, particularly if you have a chronic lung condition. See our guide to understanding pulse oximeter readings.

Do not rely on the device alone

The FDA advises against relying only on a pulse oximeter to assess your health or oxygen level. Pay attention to symptoms. Seek urgent medical help for:

• shortness of breath or difficulty breathing;
• bluish lips, face or nails;
• chest pain or tightness;
• a racing pulse;
• confusion, restlessness or unusual drowsiness.

These need attention whatever the display shows.

Good habits

• Measure at the same times each day, in the same position.
• Use the same finger.
• Keep a written log to show your doctor.
• Do not share readings between different devices; stick to one.

Care of the device

• Wipe the inside of the clip and the casing as the instructions direct. Do not immerse it in liquid.
• Store it in a dry place away from heat and direct sunlight.
• Remove the batteries if it will not be used for a long time.

Using a pulse oximeter on children

Adult fingertip oximeters may not fit small fingers and can give unreliable results in young children. Use a device intended for children, on a doctor’s advice.

The bottom line

Warm, still, rested and free of nail polish: those four conditions give a pulse oximeter its best chance of an accurate reading. Record results and act on symptoms, not just numbers. Read what to check before buying a pulse oximeter, and find devices in our medical supplies department.

Sources

1. U.S. Food and Drug Administration. Pulse Oximeters.
2. MedlinePlus. Pulse Oximetry.
3. MedlinePlus. Pulse.