Silent hypoxia (also known as happy hypoxia) is generalised hypoxia that does not coincide with

shortness of breath Shortness of breath (SOB), 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 discomfort that con ...

. This presentation is known to be a complication of

COVID-19 Coronavirus disease 2019 (COVID-19) is a contagious disease caused by the coronavirus SARS-CoV-2. In January 2020, the disease spread worldwide, resulting in the COVID-19 pandemic. The symptoms of COVID‑19 can vary but often include fever ...

, and is also known in walking pneumonia,

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

, and rebreather diving.

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, the respiratory illness responsible for the COVID-19 pandemic. The virus previously had the Novel coronavirus, provisional nam ...

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 ( thrombi) is a solid or semisolid aggregate from constituents of the blood (platelets, fibrin, red blood cells, white blood cells) within the circulatory system during life. A blood clot is the final product of the blood coagulati ...

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'' (''NYT'') is an American daily newspaper based in New York City. ''The New York Times'' covers domestic, national, and international news, and publishes opinion pieces, investigative reports, and reviews. As one of ...

'' 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 process by which care providers such as Health professional, medical professionals and those with first aid knowledge determine the order of priority for providing treatment to injured individuals and/or inform th ...

—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) synonymous with cryptogenic 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 ...

. The condition can also be first detected by using prehospital

pulse oximetry Pulse oximetry is a noninvasive method for monitoring blood 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 art ...

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 a harmful effect of high altitude, caused by rapid exposure to low amounts of oxygen at high elevation. People's bodies can respond to high altitude in different wa ...

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 microorga ...

* Inert gas asphyxiation * Occupational accidents involving asphyxiant environments *

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

malfunctions *

Technical diving Technical diving (also referred to as tec diving or tech diving) is scuba diving that exceeds the List of diver certification organizations, agency-specified limits of recreational diving for non-Professional diver, professional purposes. Technica ...

accidents

References

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