Silent Hypoxia

  • 07 May 2020

  • As medical practitioners around the world are busy treating people for Covid-19, many have reported a condition called ‘silent’ or ‘happy’ hypoxia, in which patients have extremely low blood oxygen levels, yet do not show signs of breathlessness.
  • The condition has puzzled medical practitioners, and many are now advocating for its early detection as a means to avoid a fatal illness called Covid pneumonia.

What is Hypoxia?

  • Hypoxia is a condition wherein there is not enough oxygen available to the blood and body tissues.
  • Hypoxia can either be generalised, affecting the whole body, or local, affecting a region of the body.
  • Normal arterial oxygen is approximately 75 to 100 millimetres of mercury (mm Hg), and normal pulse oximeter readings usually range from 95 to 100 per cent.


  • When levels fall below 90 percent, patients could begin experiencing lethargy, confusion, or mental disruptions because of insufficient quantities of oxygen reaching the brain.
  • Levels below 80 percent can result in damage to vital organs.

What is Silent Hypoxia?

  • It is a form of oxygen deprivation that is harder to detect than regular hypoxia.
  • In silent hypoxia, patients appear to be less in distress.
  • In many cases, Covid-19 patients with silent hypoxia did not exhibit symptoms such as shortness of breath or coughing until their oxygen fell to acutely low levels, at which point there was a risk of acute respiratory distress (ARDS) and organ failure.

Reason for Silent Hypoxia

  • The reason why people are left feeling breathless is not because of the fall in oxygen levels itself, but due to the rise in carbon dioxide levels that occur at the same time, when lungs are not able to expel this gas efficiently.
  • In patients with Covid pneumonia, the virus causes air sacs to fall, leading to a reduction in levels of oxygen.
  • However, the lungs initially do not become stiff or heavy with fluid, and remain “compliant” — being able to expel carbon dioxide and avoiding its buildup. Thus, patients do not feel short of breath.