Pulse Oximeter Alert: Poor Probe Placement Can Lead to Inaccurate Results

taking someone's pulse

Pulse oximeters are used both at home and in clinical settings to measure blood oxygen levels. However, recently experts have been warning people that poor probe placement could lead to highly inaccurate results. This may put a patient’s health in danger.

In fact, a patient safety alert has been issued by regulators in the UK warning of the risk of inappropriate placement of pulse oximeter probes. NHS Improvement says readings may be highly inaccurate if probes meant for the finger and ear are mixed up, or when devices were used to measure the wrong patient group.

What Happens if a Pulse Oximeter Probe is Inappropriately Placed?

Pulse oximeter probes are designed to be attached to either a finger or an ear. However, they are not interchangeable. Furthermore, probes also need to be selected according to the patient’s weight when babies and children are being monitored.

If a finger probe is attached to the ear or vice versa, the results may be up to 50% lower or 30% higher than the actual value.

If a reading is 30% higher, you may falsely assume that your blood oxygen levels are normal. In reality, your condition may actually be deteriorating.

If your reading is lower, you may seek out unnecessary care when your condition is actually stable or improving.

Training is Key in Clinical Settings

Part of the problem in clinical settings, experts say, is that staff are unaware that finger probes can give misleading results if placed on the ear.

A quarter of the staff surveyed by NHS Improvement said they did not have access to ear probes. Ear probes will need to be used on at least some patients – no matter the clinical setting.

Another problem is product design. Once probes are removed from packaging, there are no visible reminders of where to place the probe.

The patient alert is calling on NHS organizations to ensure that staff have access to all of the equipment they need and to educate on the dangers of inappropriately placed pulse oximeter probes. NHS Improvement is also calling on manufacturers to change their product labels to clearly indicate where to attach the probe.

How to Properly Attach a Pulse Oximeter Probe

It’s important to understand how to properly attach a pulse oximeter probe to the finger or ear. Whether you’re using an at-home device or getting tested at the doctor’s office.

If you understand how to use a pulse oximeter, you can determine whether the nurse is attaching the probe properly.

How to Attach an Ear Oximeter Probe

  • Gently clean the earlobe with an alcohol pad for 10-20 seconds.
  • Attach the probe to the earlobe or another visible part of the ear, such as the pinna.
  • Make sure the LED side of the probe is facing toward the head on the lower, fleshy area of the ear. There needs to be sufficient blood flow in order to get an accurate, solid reading. Avoid areas with cartilage, and do not press on the clip as this will restrict blood flow.
  • The LED light detector should be fully covered by the ear and not exposed to any light in the room.
  • You can use an adhesive disk to better secure the probe.
  • Leave the probe on for about three minutes until you have a stable reading.

How to Attach a Finger Oximeter Probe

  • Turn on the pulse oximeter.
  • Place the sensor on any finger (with the exception of the thumb). The sensor screen should be above the fingernail.
  • Wait for the pulse oximeter to acquire a signal. This can take 10 seconds or more.
  • Limit your movement while trying to acquire a signal, as this can affect the accuracy of the results.
  • The oxygen saturation results are typically indicated as “SpO2.”

Many finger oximeter probes can be left on the finger for continuous monitoring (common in a hospital setting). If you’re going to leave the probe on, you may want to move the sensor every 2-4 hours to prevent discomfort.

Pulse oximeter devices are relatively easy to use, but the results are only accurate if the appropriate probe is placed in the appropriate area. In a clinical setting, it’s crucial for staff to understand that ear and finger probes cannot be interchanged. Educating yourself on how to properly use an oximeter probe can help protect your health, whether you monitor at home or at the doctor’s office.

Which Pulse Oximeter Should I Use?

There are a lot of fingertip pulse oximeters on the market today. It can be quite overwhelming to choose the right one. I have put together a post that reviews my favorite pulse oximeters for use in your home or on the go. You can find that post here.

Oxygen and Pulse Monitors – Uses, Readings and How They Work


A pulse oximetry device is used to measure your oxygen saturation level. This simple device offers a painless, non-invasive way to gauge how well oxygen is being sent to the parts of your body furthest from your heart, like your arms and legs.

The readings help doctors determine whether a patient needs extra oxygen.

The History of Pulse Oximetry

German physician Karl Matthes created the first two-wavelength ear oxygen saturation meter in 1935. His was the first device to measure oxygen saturation levels. Glenn Allan Millikan was the creator of the original oximeter in the 1940s.

Bioengineers Takuo Aoyagi and Michio Kishi developed pulse oximetry in 1972. They used the ratio of red to infrared light absorption to determine oxygen saturation.

By 1987, pulse oximetry had become part of the standard of care when administering general anesthetic in the United States.

The Importance of Pulse Oximetry

Every single organ and system in the body requires oxygen to survive. When cells are deprived of oxygen, they eventually begin to malfunction and die. Cell death can ultimately lead to organ failure.

Your lungs filter the oxygen you breathe and then distribute that oxygen into the blood through the hemoglobin proteins in red blood cells. These proteins are what provide your organs, tissues and every cell in your body with oxygen.

Pulse oximetry measures the percentage of oxygen in these proteins, which indicates how much oxygen your organs are receiving.

Uses for Pulse Oximetry

Pulse oximetry devices are used to determine whether there’s enough oxygen in the blood. This information may be needed in a few different scenarios, including:

  • Checking to see how well a person handles increased activity levels.
  • During or after a procedure that requires sedation.
  • To check for sleep apnea.
  • To gauge how well lung medications are working.
  • To determine whether an oxygen concentrator is needed to help with breathing, or to see how well a ventilator is working.

A physician may also use this device to check the health of a person with a health condition that affects blood oxygen levels, which includes:

  • Anemia
  • Heart failure
  • Heart attack
  • Pneumonia
  • Lung cancer
  • Asthma
  • COPD

In some cases, a doctor may recommend using a pulse monitor to measure oxygen saturation during exercise. Physical activity can improve a patient’s overall fitness and stamina, but it can also result in shortness of breath. A finger pulse monitor can help patients keep an eye on their oxygen levels while being active.

That being said, anyone who experiences shortness of breath, dizziness and/or difficulty breathing should see a doctor right away.

Doctors may also use the device for other reasons. No matter the reason, it’s important to understand that the test is quick and painless.

Pulse Oximetry Readings

Pulse oximetry tests have fairly high accuracy rates, especially when high-quality equipment is used.

Most machines will provide results that are within a 2% difference of actual oxygen levels. That being said, there are many variables that may affect the accuracy of the reading.

Body temperature, movement and even nail polish can affect the outcome of the test.

Doctors will typically look for a reading of at least 89%, the level needed to ensure that your cells (and body) are healthy. A temporary reading that is lower than 89% is not believed to cause damage, but repeat instances of low oxygen saturation levels may indicate a problem and potential damage.

A normal, healthy individual will have an oxygen saturation level of 95%. A reading of 92% may indicate an oxygen deficiency. In other words, your tissues may not be receiving enough oxygen to stay healthy.

A reading under 90% is considered abnormal and may indicate a medical emergency. There are many reasons why oxygen saturation levels can drop, including:

  • Choking
  • Suffocation
  • Inhaling poisonous chemicals
  • Allergic reactions
  • Certain infections
  • Drowning
  • Sleep apnea
  • General anesthesia
  • Heart failure
  • Certain diseases, such as lung cancer and emphysema
  • Poor circulation or cold hands
  • Bilirubin levels
  • Changes in the pulse
  • Lipids in the blood plasma
  • Carbon monoxide poisoning

How the Device Works

A pulse oximetry device uses a probe, which is a clip-like device, to check oxygen levels. The probe is placed on a body part, such as the ear or a finger. Light is used to measure how much oxygen is in the blood.

Let’s say the probe is attached to your finger. The probe will then shine a light through your finger. Sensors will determine how much oxygen is in your blood based on how the light passes through your finger.

The probe is equipped with two LEDs: one infrared and one red. The LEDs transmit the lights’ wavelengths to a photodetector on the other side of the probe.

The device will then calculate the results and display a number on the screen. That number refers to the percentage of oxygen in the blood. The device can also measure your pulse rate.

The entire process is painless and non-invasive. Once the test is over, the probe will be removed.

Are There Any Side Effects?

A pulse oximetry device is non-invasive, so there is little risk of side effects. But some people may experience sensitivity, redness and minor irritation after use.

If the probe is fitted very tightly and for a prolonged period of time, the device may actually cut off oxygen to that part of the body. Changes in skin color, numbness and tingling are all signs that the probe is fitted too tightly.

The biggest risk is a false reading. The accuracy of the device, as mentioned previously, largely depends on having a correct fit and keeping still during the test.

If used to check for sleep apnea, for example, a person may roll over while sleeping and loosen the device, which would set off a false alert.

Because they’re so simple and easy to use, pulse oximeters are now available for consumers to purchase. Some companies market these devices to parents of infants who are concerned about sudden infant death syndrome (SIDS) and sleep accidents. But thus far, there is no research that supports claims these devices actually prevent accidents or SIDS.