Oxygen saturation in patients with chronic obstructive pulmonary disease is normal if the arterial blood gas analysis is between 80-100 mmHg. However, in patients with chronic obstructive pulmonary disease, the oxygen saturation can be affected depending on the duration of the disease, age and treatment, whether or not long-term home oxygen therapy and non-invasive ventilators are worn. In patients with chronic obstructive pulmonary disease who are not on oxygen, oxygen saturation less than 80 mmHg is considered to be hypoxemia, and less than 60 mmHg is considered to be type I respiratory failure, which requires continuous low-flow oxygenation with home oxygen therapy. If continuous low-flow oxygenation does not improve arterial blood oxygen saturation, non-invasive ventilator-assisted ventilation is required to increase ventilation, improve oxygenation, and correct hypoxemia and type I respiratory failure. Oxygen saturation greater than 80 mmHg is considered normal in patients with chronic obstructive pulmonary disease, and the older the patient is, the milder the decline in the index may be.