How to Detect the Stealthy COVID-19 Threat, Silent Hypoxia

COVID-19 Could Leave You Starving for Oxygen Without Realizing it!
Teri Krieger

Teri Krieger

Director of Sales

The recent coronavirus pandemic shocked the world, forcing a rapid global response focused on containment, fast detection, and efficient monitoring along with the development of new telehealth devices.

Years later, much of life looks like it did before the pandemic. However, there is still a significant number of daily COVID-19 cases and deaths in the US and worldwide.

One of the primary causes is hypoxemia, or low oxygen levels in the blood, which may not present with any symptom of breathlessness. This lack of any warning signs can lead people to neglect seeking medical help until it’s too late. 

Referred to as silent hypoxia, this medical condition takes its name from the fact that there is typically no breathlessness associated with it. Because of this, many patients may be completely unaware of their dangerously low oxygen levels. 

This article explores ways of monitoring COVID-19 pneumonia at home and detecting its often elusive henchman, silent hypoxia.

What is silent hypoxia?

“Silent hypoxia,” “silent hypoxemia,” or “happy hypoxia,” as the names imply, is a condition where a person does not show difficulty breathing or other symptoms associated with low oxygen levels despite having alarmingly low oxygen saturation levels.

An oxygen level (oxygen saturation) of 95 to 100% is normal for healthy individuals. A reading lower than 95% could require a doctor’s care, and a reading lower than 90% would likely require emergency care.

Normally, a person who is experiencing a significant drop in their oxygen level would experience any of the following symptoms:

  • Shortness of breath
  • Restlessness
  • Anxiety
  • Low blood pressure (hypotension)
  • Bluing of the skin (cyanosis)
  • Excessive or abnormal sweating (diaphoresis)

In contrast,  some people with COVID-19 pneumonia, a complication of COVID-19, experience a significant drop in their oxygen level but do not show any of the symptoms listed above. Some of these patients even have low oxygen levels and could be on the brink of organ failure or unconsciousness. Instead, they are awake and talking with minimal distress.

Some may go to the hospital exhibiting mild fever and upper respiratory signs such as coughing but without intense breathing difficulty and only detect severe hypoxia after pulse oximetry or blood gas analysis. 

In some cases, silent hypoxia was the only clinical feature of an acute COVID-19 infection. This means that a person may be completely symptom-free but have deficient oxygen levels on pulse oximetry. 

There are even documented reports of people with a COVID-19 infection who were only “mildly ill” and receiving treatment at home who developed sudden-onset respiratory failure and died because of the condition.

Because of the subtle nature of silent hypoxia, the CDC recommends healthcare professionals monitor their patients with COVID-19 who are isolated in their homes with pulse oximetry. This ensures fast recognition and treatment of low oxygen levels, which can be life-threatening.

Silent hypoxia has been reported to occur in 32 to 65% of people with COVID-19 and more than half of those severely ill with COVID-19. Experts still do not know the reason behind silent hypoxia in COVID-19. However, a retrospective study found that certain factors put a person at risk of developing silent hypoxia. These include:

  • Old age (> 65 years old)
  • Male sex
  • Body mass index (BMI) of 25 or higher
  • Active smokers
  • Having certain medical conditions (diabetes, chronic obstructive pulmonary disease, and other chronic lung diseases)


How physicians check your blood oxygen level

Physicians typically use two objective tests when measuring blood oxygen levels, a blood gas analysis and pulse oximetry.

What is blood gas analysis, and how can it be used to detect silent hypoxia?

A blood gas analysis or arterial blood gas (ABG) analysis involves a healthcare provider collecting a blood sample for analysis in a lab or a portable machine. This is done within 10 minutes of the procedure to ensure the accuracy of the results.

What is pulse oximetry, and how can it be used to detect silent hypoxia?

Pulse oximetry is a non-invasive and straightforward procedure that uses a portable electronic device called a pulse oximeter, or simply a pulse ox, to estimate the oxygen level in your red blood cells. 

It works by sending infrared light through your fingertip and measuring how much of it is absorbed by your blood. 

You can attach pulse oximeters to your fingers, forehead, nose, foot, toes, or ears.

Limitations of Pulse Oximetry

The pandemic has caused increased use of at-home pulse oximeters. But while pulse oximeters are helping people estimate their blood oxygen levels from home, the American Lung Association warns against relying solely on blood oxygen levels to detect COVID-19.  

Most people with the virus would present with more common initial symptoms such as fever and cough.

FDA warns of risk of inaccurate measurements from home

While the level of inaccuracy of pulse oximeters may be small and not clinically significant, the US Food and Drug Administration (FDA) cautioned that “there is a risk that an inaccurate measurement may result in unrecognized low oxygen saturation levels.”  

 Other factors can affect the accuracy of a pulse oximeter reading. These include:

  • Poor circulation
  • Dark skin pigmentation
  • Cool skin temperature
  • Thick skin
  • Current use of tobacco
  • Use of finger polish or artificial nails
  • Unclean nails


In search of an FDA-cleared pulse oximeter device 

Over-the-counter (OTC) and virtual pulse oximeter apps on smartphones are sold directly to customers in stores as general wellness or sporting/aviation products. It is important to note that it’s unsafe to assume they’ve undergone an FDA review.

In contrast, prescription oximeters are reviewed by the FDA and receive a 510(k) clearance. These devices undergo clinical testing to confirm their accuracy. You can often find these pulse oximeters in doctor’s offices and hospitals. Doctors also prescribe them for home use. 


Nonagon’s FDA-cleared N9+ device — pulse oximeter plus 8 more physical exams

The Nonagon N9+ is an FDA-cleared innovative device that lets you obtain clinical-grade oxygen saturation levels. But unlike regular oximeters, the N9+ also enables you to capture other crucial health data conveniently in your home. These include your temperature, heart rate, and heart, lung, and abdominal sounds—all of which can offer crucial information to your doctor about your health if you are managing your COVID-19 in your home. 

Aside from clinically accurate results, you can pair the N9+ with your phone to quickly provide your doctor with the health information they need to monitor your condition and decide on the best treatment based on your health status.



Aside from relying on virtual rapid COVID-19 tests, pulse oximetry is an easy-to-use and convenient way to measure blood oxygen levels for people managing their COVID-19 at home.

It can help detect silent hypoxia, a potentially life-threatening condition characterized by decreased oxygen levels in the blood.

However, it is essential to note that not all pulse oximeters are intended for medical use. Make sure you use a clinically accurate FDA-cleared oximeter, like the Nonagon N9+, to get reliable and precise results.

It is also important to remember that even if you get an accurate pulse oximeter reading, it doesn’t replace the need to immediately inform your doctor about the onset of any other COVID-19 symptoms you may experience.


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