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Silent Hypoxia with COVID-19

August 16, 2022 - Parul Saini, Webmedy Team

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.


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.


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