Five percent of patients with COVID-19 progressed to respiratory failure and required ICU admission. Attention should be paid to patients over 65 years of age who have severe underlying diseases (cancer, respiratory diseases, cardiovascular and cerebrovascular diseases, chronic renal failure, autoimmune deficiency diseases, etc.) and have not completed the whole course of vaccine, and such patients often have abnormal oxygen tolerance, that is, a significant decrease in skin finger pulse oxygen saturation (SpO2) can occur after daily activities. Basal SpO2 at admission is often associated with prognosis, but it is difficult to differentiate prognosis from responsiveness to treatment by changes in SpO2 after oxygen therapy is administered clinically. However, there is still a lack of clinical indicators to predict the prognosis and treatment responsiveness of COVID-19.
