The concentration of oxygen absorbed by nasal catheter cannot be calculated accurately, usually the nasal catheter is given according to the flow of oxygen absorbed, and the concentration of oxygen absorbed can be estimated based on the flow of oxygen absorbed. In general, the oxygen concentration is close to the oxygen concentration in the air (21%) + oxygen flow rate x 4%. However, this formula has certain conditions, the patient’s breathing should be relatively stable, and the oxygen flow rate should not be too high. If the patient’s breathing is too deep or too shallow, and the flow rate of oxygen inhalation is too high, it will cause a large deviation between the calculated result and the actual oxygen concentration inhaled. In addition, the oxygen concentration inhaled through nasal catheter is hardly more than 50%. If the patient needs to give higher concentration of oxygen, it is necessary to change the way of oxygen inhalation, such as giving oxygen storage mask for oxygen inhalation, or giving high flow wet oxygen therapy through the nose for oxygen inhalation.