Silent hypoxia (also known as happy hypoxia) is generalised

hypoxia Hypoxia means a lower than normal level of oxygen, and may refer to: Reduced or insufficient oxygen * Hypoxia (environmental), abnormally low oxygen content of the specific environment * Hypoxia (medical), abnormally low level of oxygen in the tis ...

that does not coincide with

shortness of breath Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing disc ...

. This presentation is known to be a complication of

COVID-19 Coronavirus disease 2019 (COVID-19) is a contagious disease caused by a virus, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The first known case was COVID-19 pandemic in Hubei, identified in Wuhan, China, in December ...

, and is also known in

walking pneumonia Atypical pneumonia, also known as walking pneumonia, is any type of pneumonia not caused by one of the pathogens most commonly associated with the disease. Its clinical presentation contrasts to that of "typical" pneumonia. A variety of microorgan ...

altitude sickness Altitude sickness, the mildest form being acute mountain sickness (AMS), is the harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People can respond to high altitude in different ways. Sympt ...

, and

rebreather diving Rebreather diving is underwater diving using diving rebreathers, a class of underwater breathing apparatus which recirculate the breathing gas exhaled by the diver after replacing the oxygen used and removing the carbon dioxide metabolic produc ...

Causes

One theory relating to COVID-19 presentation suggests the impaired processing of severe hypoxia and resumption of normal breathing may be due to the neurological pathway by which the virus spreads from the oral cavity to the brain. It is speculated that this condition is caused by

SARS-CoV-2 Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19 (coronavirus disease 2019), the respiratory illness responsible for the ongoing COVID-19 pandemic. The virus previously had a ...

affecting the blood flow of the lungs' airways, in addition to the blood vessels within the lungs, which must match in order to allow proper airflow, but not affecting them enough to cause shortness of breath. It is also speculated that silent hypoxia may be caused by the formation of small

blood clots A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cr ...

within the lungs. It has been shown that the breathing rates of patients with COVID-19 gradually increase, which in turn leads to silent hypoxia. It has also been shown that COVID-19 patients experience lesser levels of shortness of breath after exercise than non-COVID-19 patients. In healthy people this presentation can occur when the person breathes a gas which has a low oxygen content, and also a low carbon dioxide content, so there is no hypercapnic alarm response.

Presentation

In a ''

New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid d ...

'' opinion piece (April 20, 2020), emergency room doctor Richard Levitan reported: "A vast majority of Covid pneumonia patients I met had remarkably low oxygen saturations at

triage In medicine, triage () is a practice invoked when acute care cannot be provided for lack of resources. The process rations care towards those who are most in need of immediate care, and who benefit most from it. More generally it refers to prio ...

—seemingly incompatible with life—but they were using their cellphones as we put them on monitors."

Diagnosis

A tool used to diagnose silent hypoxia is the six-minute walk test, (6MWT), wherein a patient walks at a normal pace for six minutes, in order to monitor their physiological response. It has been proven that, after performing the 6MWT, COVID-19 patients were more likely to develop exercise-induced hypoxia symptoms than non-COVID-19 patients who had

idiopathic pulmonary fibrosis Idiopathic pulmonary fibrosis (IPF), or (formerly) fibrosing alveolitis, is a rare, progressive illness of the respiratory system, characterized by the thickening and stiffening of lung tissue, associated with the formation of scar tissue. It is ...

. The condition can also be first detected by using prehospital

pulse oximetry Pulse oximetry is a noninvasive method for monitoring a person's oxygen saturation. Peripheral oxygen saturation (SpO2) readings are typically within 2% accuracy (within 4% accuracy in 95% of cases) of the more accurate (and invasive) reading of ...

Treatment

Treatment depends on the cause. In some cases supplementary oxygen is needed, in severe cases artificial ventilation may be necessary. In mild cases where the cause was hypoxic breathing gas, it may only be necessary to return to a normally oxygenated environment. Underlying medical problems may require assessment and treatment.

Prognosis

The prognosis for silent hypoxia in COVID-19 is generally poor, as oxygen levels in the blood can drop below 50 percent without being noticed. In cases where a healthy person was exposed to a hypoxic environment, the outcome will usually depend on the extent of associated tissue damage incurred. In mild cases a quick return to normal follows reversion to normally oxygenated breathing gas.

Epidemiology

Known to be associated with: *

Altitude sickness Altitude sickness, the mildest form being acute mountain sickness (AMS), is the harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People can respond to high altitude in different ways. Sympt ...

Atypical pneumonia Atypical pneumonia, also known as walking pneumonia, is any type of pneumonia not caused by one of the pathogens most commonly associated with the disease. Its clinical presentation contrasts to that of "typical" pneumonia. A variety of microorgan ...

Inert gas asphyxiation Inert gas asphyxiation is a form of asphyxiation which results from breathing a physiologically inert gas in the absence of oxygen, or a low amount of oxygen, rather than atmospheric air (which is composed largely of nitrogen and oxygen). Examples ...

* Occupational accidents involving asphyxiant environments *

Rebreather A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's breathing, exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. ...

malfunctions *

Technical diving Technical diving (also referred to as tec diving or tech diving) is scuba diving that exceeds the agency-specified limits of recreational diving Recreational diving or sport diving is diving for the purpose of leisure and enjoyment, usually ...

accidents

References

{{authority control Impact of the COVID-19 pandemic on other health issues Respiratory diseases