Happy Hypoxia in COVID-19
16 June 2021
Diseases often show symptoms to express degree of severity. Symptoms are alert by the body about occurrence of a pathological disorder. Corona virus disease shows respiratory symptoms like shortness of breath, cough, chest discomfort and hypoxia. Hypoxia is a serious condition affecting vital body functions and organs like kidney, heart, brain. Some patients often have decreased oxygen saturation levels on pulse oximetry reading but with out respiratory distress. This is called Happy hypoxia (a general term). The medical term is silent hypoxemia or apathetic hypoxia.
Patients often affect pneumonia associated with COVID-19 has oxygen deprivation with about 50% of saturation level unlike usual symptoms of pneumonia like chest pain, breathing difficulties. In pneumonia, the alveoli filled with pus or fluid produce congestion, chest pain, while in COVID-19, the alveoli collapse, retaining its ability to expel carbon dioxide, rendering the patient to experience a normal breathing pattern. This drawback makes failure in early detection of pneumonia. Fever and chills may dominate other symptoms making the patient to neglect decreased respiratory rate, meanwhile the body compensate with oxygen deprivation. An oxygen saturation below 80% is considered to be serious medical condition but covid patients sometimes appears to be active without any breathing difficulties even in oxygen saturation below 80%. Effective oxygenation does not occur but the patient is conscious, without sensation of suffocation. Several hypoxemia patients may later present with cognitive impairment and confusion .
Due to inflammatory reaction caused by SARS-COV-2, cellular proteins are released leading to coagulation of small arteries of lungs. Release of histamine or stimulation of juxtacapillary receptors within the pulmonary vasculature modulates obstruction causing hypoxia. Another mechanism thought is, expression of SARS-COV-2 in carotid body where chemoreceptors sense oxygen. Hypoxemia stimulates carotid bodies to send signals to respiratory center, medulla oblongata, which stimulates increased ventilation by passing efferent signals via phrenic nerves and to the diaphragm. The respiratory center is highly sensitive to even a small increase in carbon dioxide level. An increase in partial pressure of carbon dioxide to at least 10 mm Hg is intolerant and produces dyspnoea. However on patients with silent hypoxemia, there was an increase in PaCO2 up to 39 mm Hg. Diabetic patients and people above 60 year of age are more prone for silent hypoxemia, as they are observed with a blunted response of respiratory center to hypoxia, thereby decreasing the respiratory response by 50%. In diabetic patients, they have decreased ability to perceive respiratory sensation.
Identifying happy hypoxia
Asymptomatic patients might have silent hypoxemia, fortunately most of the patients recover without the need of intubation. Change in the colour of lips from natural tone to blue, skin discolouration to red or purple tone or profuse sweating even when not doing strenuous physical work could be symptoms of happy hypoxia. Measurement of blood oxygen saturation with pulseoximeter is recommended for COVID-19 patients to rule out the risk of silent hypoxia. Individuals must rest for at least 10-15 minutes before checking saturation. Keep the hand still on chest at heart level, twice daily for healthy individuals and every 6 hours for covid patients. Oxygen saturation can be measured using certain smart-phone based pulseoximeter.