COVID-19: How do we explain 'happy' hypoxemia?
New research suggests that the seemingly unusual phenomenon of “happy” hypoxia, or silent hypoxemia, in people with COVID-19 can be explained by long-established principles of respiratory science.
A new study has suggested that “long-established principles of respiratory physiology” can explain the otherwise confusing presence of silent hypoxemia patients with COVID-19.
The research, published in the American Journal of Respiratory and Critical Care Medicine, may help clinicians better support patients with severe cases of COVID-19.
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The ongoing COVID-19 pandemic holds many mysteries. Among the more baffling has been the frequency of silent hypoxemia, or happy hypoxia, as it has been dubbed in the media.
Hypoxemia is defined as “a decrease in the partial pressure of oxygen in the blood.” As blood oxygen levels begin to reduce, a person may experience shortness of breath, also called dyspnea. If blood oxygen levels continue to fall, the organs may shut down, and the issue becomes life threatening.
COVID-19 is primarily a respiratory illness, and a severe case can reduce the amount of oxygen that the lungs can absorb. Blood oxygen levels have been found to be very low in some COVID-19 patients.
As reported in various media sources, including Science, despite low blood oxygen levels, some patients appear to be functioning without serious issues or even shortness of breath.
According to the authors of the present research, the condition “is especially bewildering to physicians and is considered as defying basic biology.”
The lead author of the study, Dr. Martin J. Tobin — a professor of pulmonary and critical care medicine at the Loyola University Medical Center, in Maywood, IL — noted that “In some instances, the patient is comfortable and using a phone at a point when the physician is about to insert a breathing [endotracheal] tube and connect the patient to a mechanical ventilator, which, while potentially lifesaving, carries its own set of risks.”
To understand why this is the case, Dr. Tobin and colleagues first conducted an informal survey of 58 healthcare workers asking whether they had encountered cases of silent hypoxemia, or happy hypoxia. The team received 22 responses with useful data.
After analyzing the data, the authors concluded that many of the cases of silent hypoxemia could be explained through conventional respiratory science.
For example, a healthcare provider typically first measures oxygen levels with a pulse oximeter. Dr. Tobin points out that “while a pulse oximeter is remarkably accurate when oxygen readings are high, it markedly exaggerates the severity of low levels of oxygen when readings are low.”
Dr. Tobin also noted that the brain may not immediately recognize that blood oxygen levels have reduced, explaining, “As oxygen levels drop in patients with COVID-19, the brain does not respond until oxygen falls to very low levels — at which point, a patient typically becomes short of breath.”
In addition, more than half of the patients with silent hypoxemia also had low carbon dioxide levels, which Dr. Tobin and his co-authors believe could reduce the effect of low blood oxygen levels.
“It is also possible that the coronavirus is exerting a peculiar action on how the body senses low levels of oxygen,” said Dr. Tobin, speculating that this could be linked to the lack of smell that many COVID-19 patients experience.
As the initial wave of the disease is quelled, new outbreaks across the world raise the specter of a second wave. COVID-19’s sudden emergence and rapid spread gave scientists and clinicians little information to go on when determining effective treatments.
Now, with real-world data to guide future treatments, learning from this information will be crucial in reducing the number of people who die of the disease.
While verifying the explanations that the present study proposes will require further research, the study contributes to a growing body of research that will prove invaluable for clinicians working in critical care wards.
For Dr. Tobin, “This new information may help to avoid unnecessary endotracheal intubation and mechanical ventilation, which presents risks, when the ongoing and much anticipated second wave of COVID-19 [fully] emerges.”
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