Silent Hypoxia with COVID-19

August 16, 2022 - Parul Saini, Webmedy Team

Updated Version - July 21, 2023

Happy Hypoxia or Silent Hypoxia has turned out to be one of the most serious symptoms common among a large section of Covid patients, leaving doctors confused and alarmed.


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How is Silent or Happy Hypoxia different from Hypoxia?

Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level. This can result from inadequate oxygen delivery to the tissues either due to low blood supply or low oxygen content in the blood (hypoxemia).

Silent Or Happy Hypoxia

While an increased respiratory rate (tachypnoea) is seen in normal hypoxic patients. It is NOT typically found in patients with silent hypoxia. Happy hypoxia does not coincide with shortness of breath.

With Silent hypoxia, there is a silent drop in oxygen below critical level without any pressing symptoms or breathing distress. In happy hypoxia, a person's oxygen levels are so low that they should be fainting or experiencing organ damage, but instead, they are seemingly well, until eventually, they collapse.

A near-normal blood oxygen saturation level is more than 90%, with 94-100% considered normal. If a patient registers a number lower than this, the brain might not get the oxygen it needs, leading to confusion and lethargy. If the level drops as far as the low 80s, there's a real danger of damage to vital organs and even death.

Unfortunately, hypoxia, silent hypoxia, and the need for supplementary oxygen are all predictors of worse outcomes in COVID-19 patients.

Silent hypoxia isn't a new phenomenon. It's been seen in high altitude sickness. Any condition that causes damage to the lungs can cause it, although it's more common in chronic conditions like COPD (Chronic Obstructive Pulmonary Disease) and Pulmonary Fibrosis, where the lungs are chronically damaged.

Why does Silent Hypoxia occur in Covid Patients?

  • Loss of Ability of Restricting Blood Flow in Lungs

    Normally, if areas of the lung aren't gathering much oxygen due to damage from infection, the blood vessels will constrict in those areas. This is actually a good thing that our lungs have evolved to do, because it forces blood to instead flow through lung tissue replete with oxygen, which is then circulated throughout the rest of the body. But the lungs of some COVID-19 patients lose the ability of restricting blood flow in lungs.

  • Blood Clotting in Lungs

    When the lining of blood vessels get inflamed from COVID-19 infection, tiny blood clots too small to be seen on medical scans can form inside the lungs, this could incite silent hypoxia.

  • Interference with Normal Ratio of Air-to-Blood Flow

    COVID-19 interferes with the normal ratio of air-to-blood flow that the lungs need to function normally. This can be a possible contributor to the severe, silent hypoxia.

A combination of all three factors are likely to be responsible for the severe cases of Silent Hypoxia in some COVID-19 patients.

Ways to detect Silent or Happy Hypoxia in Covid Patients

  • Monitoring of Arterial Oxygen Saturation

    Constant monitoring of arterial oxygen saturation by pulse oximeter is a very good option to detect silent hypoxia. This device might be helpful for confirmed COVID-19 patients who are currently not demonstrating any severe symptoms of reduced oxygen saturation in the blood.

  • Arterial Blood Gas Analysis

    Arterial blood gas analysis is a process where a sample of blood is taken from the artery to check the concentration of different gases in the blood. Right evaluation of blood sample through this method can provide a wide range of standard parameters such as partial pressure of oxygen and carbon dioxide, which are useful to investigate acidosis, alkalosis, as well as silent hypoxia. Blood gas analysis together with a pulse oximeter could be a valuable medium for the early detection of silent hypoxia in COVID-19 patients.

  • Six-minute Walk Test (6MWT)

    A tool used to diagnose silent hypoxia is the six-minute walk test, in which oxygen saturation level is measured before and after 6 minutes of taking walks. It has been reported that oxygen saturation level significantly reduced by 3% or more from baseline in COVID-19 patients with silent hypoxia.

Symptoms to Watch for Silent Hypoxia

  • Dis-colouration of skin to red or purple tone.
  • Change of the colour of lips from natural tone to blue.
  • Profuse sweating even when not doing hard physical work.
  • Persistent Sweating.

Diagnosis of silent hypoxia for COVID-19 Patients

Early detection of silent hypoxia in COVID-19 patients is crucial to minimize the long-term effect as well as mortality rate. Besides, early detection may facilitate deciding on when to start the oxygen treatment.


If doctors recognize silent hypoxia early enough, it can be treated with oxygen therapy (through nasal tubes, a face mask, or a tube placed in the windpipe).

Positioning patients in the upright or semirecumbent position (where the head and torso are at an angle of 45 degrees), or in the prone position (lying on their belly) might help. Also, close monitoring via blood tests is also important.

Helpful Information

What is silent hypoxia in COVID-19 patients?

Silent hypoxia, also known as happy hypoxia, is a condition where COVID-19 patients have dangerously low levels of oxygen in their blood, but don't exhibit signs of respiratory distress or discomfort, such as shortness of breath. It's been a puzzling and concerning phenomenon for medical professionals.

How is silent hypoxia detected in COVID-19 patients?

Silent hypoxia can be detected through pulse oximetry, a non-invasive method that measures the oxygen saturation in a person's blood. It's usually performed with a small device that clips onto the finger. Any reading below 95% is considered abnormal.

What are the risks associated with silent hypoxia in COVID-19?

Silent hypoxia can lead to serious complications, including sudden respiratory failure. Because patients may feel relatively well even as their oxygen levels drop, they may not seek medical help until their condition has significantly worsened.

Why does silent hypoxia happen with COVID-19?

The exact mechanism causing silent hypoxia in COVID-19 patients is not fully understood. It's speculated that the virus might damage the lungs in a way that prevents the normal response to low oxygen levels. Other theories suggest that the virus may interfere with the body's oxygen sensing mechanisms.

Can silent hypoxia be prevented in COVID-19 patients?

There is no specific way to prevent silent hypoxia. However, close monitoring of oxygen levels in people with COVID-19, especially those at high risk for severe disease, can help detect this condition early.

What is the treatment for silent hypoxia in COVID-19?

The treatment for silent hypoxia usually involves supplemental oxygen to correct the low oxygen levels. In severe cases, mechanical ventilation may be required. Early detection and treatment of silent hypoxia can significantly improve a patient's prognosis.

How common is silent hypoxia in COVID-19?

The exact prevalence of silent hypoxia in COVID-19 is not known as it varies among patients. However, multiple reports have highlighted cases of silent hypoxia, indicating that it is a significant clinical feature of COVID-19.

Can a pulse oximeter help detect silent hypoxia at home?

Yes, a pulse oximeter can help detect silent hypoxia at home. It's a small device that clips onto a finger and can provide a quick assessment of a person's oxygen saturation level. A reading below 95% should prompt immediate medical attention.

Why is silent hypoxia dangerous in COVID-19?

Silent hypoxia is dangerous because it can lead to significant damage to vital organs that require a constant supply of oxygen, like the heart and brain, before symptoms become noticeable. It can also rapidly progress to severe respiratory failure, which can be life-threatening.

Are there any specific symptoms of silent hypoxia in COVID-19?

The challenge with silent hypoxia is that it often presents without typical symptoms like shortness of breath or feeling of suffocation. However, some patients may experience subtle symptoms like fatigue, confusion, increased heart rate, or a sense of unease.

Who is at risk for silent hypoxia with COVID-19?

Anyone with COVID-19 can potentially develop silent hypoxia, but it's more common in people with severe disease. Certain underlying health conditions, like heart disease or respiratory conditions, may also increase the risk.

Can silent hypoxia lead to long-term health issues?

Silent hypoxia can potentially lead to long-term health issues, especially if not detected and treated promptly. Sustained low levels of oxygen can cause damage to vital organs and may contribute to long COVID, a condition where symptoms persist for weeks or months after the acute illness.

What research is being done on silent hypoxia in COVID-19?

Research is ongoing to better understand silent hypoxia in COVID-19, including its causes, prevalence, and optimal management strategies. Understanding this phenomenon can help improve patient outcomes and guide future treatment protocols.

How long does silent hypoxia last in COVID-19 patients?

The duration of silent hypoxia in COVID-19 patients varies and depends on several factors, including the severity of the disease, the patient's overall health, and the timeliness of treatment.

Does silent hypoxia affect recovery from COVID-19?

Silent hypoxia can potentially affect recovery from COVID-19. If not detected and treated early, it can lead to serious complications like organ damage or acute respiratory distress syndrome, which can prolong the recovery period.

Can silent hypoxia occur after recovery from COVID-19?

It's not typical for silent hypoxia to occur after recovery from COVID-19. However, some patients may experience ongoing respiratory issues after the acute phase of the illness, and it's important for these individuals to continue monitoring their oxygen levels.

Does silent hypoxia cause chest pain in COVID-19 patients?

Silent hypoxia itself doesn't usually cause chest pain. However, COVID-19 can cause a variety of other complications that result in chest pain, such as myocarditis or pulmonary embolism.

Is silent hypoxia unique to COVID-19?

While silent hypoxia has been notably observed in COVID-19, it's not unique to this disease. It can also occur in other conditions that affect oxygen levels in the blood, such as sleep apnea, altitude sickness, and certain lung diseases.

Does silent hypoxia affect the brain in COVID-19 patients?

Prolonged low oxygen levels, as seen in silent hypoxia, can potentially affect the brain. The brain requires a constant supply of oxygen to function properly, and hypoxia can lead to symptoms such as confusion, dizziness, or even loss of consciousness.

Is silent hypoxia a sign of severe COVID-19?

Silent hypoxia can be a sign of severe COVID-19, as it suggests significant lung involvement. However, because it often occurs without noticeable symptoms, it's essential to monitor oxygen levels in high-risk patients or those with known COVID-19 infection.


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