What Is a Handheld Oximeter, and How Does It Work?

A handheld pulse oximeter is a device used to measure patients’ oxygen saturation levels (SpO2) and pulse rate. They’re designed for optimal portability and ease of use in hospital and home settings. Handheld pulse oximeters are non-invasive. The device is placed on extremities far from the heart to measure blood oxygen level and pulse count. These may include the hands, feet, or ears. Handheld pulse oximeters vary in size, cost, and features. There are also special designs for infants and adults.

The Food and Drug Administration (FDA) categorizes pulse oximeters into two main categories:

  • Prescription handheld pulse oximeters: The FDA mandates that prescription oximeters must undergo clinical testing to ensure accuracy. These devices for pulse oximetry are common in clinics and hospital setups, but a doctor can prescribe them for home use, depending on the condition.
  • Over-the-counter (OTC) handheld pulse oximeters: The OTC oximeters are not approved by the FDA and hence not fit for medical purposes. They’re available in pharmacies and online platforms. However, these devices are not recommended for medical diagnosis. In most cases, OTC oximeters are useful for sports or general wellness.

According to the American Thoracic Society, the use of these devices increased over the COVID-19 pandemic as most people sought to monitor their oxygen saturation, a factor affected by the disease. The pandemic has led to more awareness of pulse oximetry and its importance in monitoring the health of people with certain conditions.


A Brief History of Pulse Oximeters

The first pulse oximeter was developed in 1974 by Dr. Takuo Aoyagi, a Japanese Bioengineer. Dr. Takuo, who died in Tokyo on April 18, 2020, made the first modern pulse oximeter used commercially. The electronic equipment used ratios of red and infrared light to detect the pulse at the measuring site. Other notable inventors include Karl Matthes and Glenn Millikan.

The idea behind a pulse oximeter can be traced back to the 1930s when Karl Matthes, a German physician, used red and green wavelengths to measure ear oxygen saturation. Glenn Allan Millikan and Earl Wood further improved the idea in 1940  as they added a pressure capsule on the device to squeeze blood into the ear while taking a reading. However, the method was not clinically fit as the light sources and photocells were unstable.

In the 1960s, Robert Shaw, a San Francisco surgeon, improved the ear oximeter by including eight wavelengths of light to help the device give a more extensive reading. By then, the pulse oximeter was huge and needed to be wheeled around the hospital. The downside was it was too expensive. 

Building on years of research and developments in pulse oximetry, Dr. Takuo looked into how the heart pulse rate could be used to measure arterial oxygen levels. He presented the idea to his then employer, Nihon Kohden, which led to the launch of the Oximeter OLV-5100 in 1975.  

The first ear oximeter wasn’t a commercial hit, as expected. However, that didn’t stop the launch of the first fingertip pulse oximeter in 1977. Based on the same principle, different companies introduced other types of pulse oximeters. The last modern protégé of pulse oximeters by Dr. Aoyagi ensured the test was non-invasive and painless.


How Handheld Pulse Oximeters Work

According to experts, a healthy adult should record 95–100% saturation levels and a heart rate of 60–100 beats per minute. A lower reading will alert the physician about whether you require oxygen supplementation therapy or what the next step should be. 

The blood that flows in your vessels contains hemoglobin, the oxygen-carrying component in the body. After oxidation in the lungs, the oxygenated blood is circulated all over the body to ensure the body parts and other organs are functioning correctly. The pulse oximeter can be placed on the hand, fingertip, earlobe, forehead, or wrist to measure blood oxygen and pulse rate. So how do they work?

Handheld pulse oximeters, also known as SAT monitors, measure the blood oxygen level using wavelength light sensors. The part with the reusable sensor is attached to the body part, while the other end is plugged into a monitor screen or power unit. The device is electronically powered, and the screen displays the pulse rate and SpO2 levels.

Pulse oximeters are compatible with various types of oxygen sensors regardless of whether the intended site is the hand, foot, earlobe, toe, or finger. The sensors are reusable or disposable, meaning the doctor can use the same machine on several patients to get a reading.

The technology behind pulse oximeters uses red and infrared LEDs. The light shines on the skin in an area that is highly vascularized. Oxygenated hemoglobin absorbs the infrared light and allows the red light to pass through it, making it possible to get a reading. On the other hand, deoxygenated hemoglobin absorbs red light while allowing the infrared to pass through. 

The oxygen saturation reading depends on the ratio of red light to infrared light transmitted through the blood. First, the device calculates the intensity of both lights on oxygenated and deoxygenated blood. Then it gives the SpO2 levels, followed by the pulse rate.


General Features of a Handheld Pulse Oximeter

Some manufacturers take the extra step of incorporating other features into the handheld pulse oximeter to enhance efficiency. These include the following:

  • Data storage memory helps the hospital collect patients’ data concerning SpO2 levels and pulse rate.
  • Audible alarms notify patients and medical staff when SpO2 levels are critical.
  • Rechargeable batteries save the person or institution the cost of purchasing a new set now and then.
  • Output ports allow data transfer and communication to other devices, such as printers.
  • Monitor/screen displays the oxygen readings


How to Take a Reading on a Handheld Pulse Oximeter 

Here is how to take a reading on a handheld pulse oximeter:

  1. First, remove any form of jewelry or watch present at the intended location. Any nail polish on your finger requires removal too.
  2. Keep your hand warm and relaxed, and let it rest below the heart level. 
  3. Attach the device to the hand and finger clip if need be.
  4. Keep the pulse oximeter on until you get a stable reading on your oxygen saturation levels and pulse rate. 
  5. Unplug the device and remove it after the test is complete. 
  6. The doctor can take a repeat test if necessary to verify the levels.

After taking a reading, here is how to interpret the results:

  • The levels are 95% and higher in healthy persons under normal conditions. 
  • A medic will conduct monitoring and respiratory assessment in persons with a reading of between 82–92%.
  • Oxygen levels between 85–94% are mildly hypoxic and may require oxygen therapy. Hypoxia is common in persons with chronic obstructive pulmonary disease (COPD) or underlying respiratory conditions. 
  • Levels of less than 85% mean the patient is severely hypoxic and requires immediate oxygen supplementation and other medical interventions.


Beneficial Features of a Handheld Pulse Oximeter

Below are some of the key features of a handheld pulse oximeter:

  • Portable design: Handheld pulse oximeters are compact and portable, making them easy to carry as they can fit in your bag. 
  • Data memory storage: Handheld pulse oximeters come with a data memory storage feature, allowing you to record readings for future reference.  
  • Range of options: Handheld pulse oximeters are available for infants, pediatrics, and adults. Medical facilities also have handheld devices for all options. 
  • Prompt results: Taking an oxygen saturation reading is easy and non-invasive. The test is also painless, taking a matter of seconds.
  • Reusable: Medics use the pulse oximeter on several patients without fear of spreading any disease or infection. When using it at home, you can use the same device to take multiple tests.  
  • Multiple power options: Many handheld pulse oximeters offer more than one power option. However, most are battery-powered and support attachment to the power docking station.
  • User-friendly: The screen is large enough to display values that are easy to read. No special skills are required to use a handheld pulse oximeter as the procedure is straightforward.


Applications of a Handheld Pulse Oximeter

A handheld pulse oximeter comes in handy for patients with chronic illnesses or those with respiratory complications. Some of the health conditions that demand monitoring of SpO2 levels are as follows:

  • Anemia 
  • Asthma
  • Bronchiectasis 
  • COPD 
  • COVID-19
  • Cystic fibrosis
  • Heart disease
  • Lung cancer
  • Lung disease or lung damage
  • Pneumonia

The main use of a pulse oximeter is oxygen saturation and pulse rate reading. A physician will require these readings for the following reasons:

  • Assess whether the patient requires supplemental oxygen therapy
  • Determine if assisted breathing is necessary
  • Assess if the lung medication administered is working 
  • Consider if ventilation is needed
  • Determine the patient’s tolerance to physical activity
  • Evaluate the seriousness of cases like sleep apnea 
  • Monitor oxygen saturation during a stress test
  • Monitor the state of the patient in surgery and under anesthesia 


Limitations of a Handheld Pulse Oximeter

Pulse oximeters, especially those that aren’t FDA approved, have inaccuracies and limitations. You are encouraged to report faulty pulse oximeters through the MedWatch Voluntary Reporting Form.

Below are some limitations or factors that affect the accuracy of handheld pulse oximeter:

Nail Polish and False Nails

Having nail polish or fake nails on can interfere with the oxygen saturation reading. You must remove the polish and false nail when undergoing the test. The color of the polish can absorb the light intended to detect oxygenated hemoglobin, leading to inaccurate pulse oximetry readings.

Exposure to Direct Bright Light

Bright light shining directly at the device can compromise the SpO2 reading. The examination room needs to be lit adequately. However, avoid exposure to shiny bright light from sunlight or operating light.

Uncomfortable Patients 

The pulse oximetry reading may be inaccurate if the patient is uncomfortable and keeps moving. A nervous or uneasy patient may keep fidgeting or shivering. The medic should hold their hand until they are calm before proceeding with the test. 

Darker Skin Tones

Research indicates discrepancies in pulse oximeters based on skin tone. For instance, some cases of occult hypoxemia are not detected by the pulse oximeter but by blood gas measurement test. Researchers intend to further evaluate the association between skin pigmentation and oximeter accuracy.


Take Away

Despite the above limitations, handheld pulse oximeters have proven beneficial in hospitals, homes, and other settings in monitoring SpO2 levels among patients and athletes. When buying one, ensure it’s certified by the relevant authorities because the higher the quality, the more accurate the results will be.