Mixed Acid-Base Disturbances refers to the simultaneous presence of two or more simple acid-base disorders. In mixed acid-base disorders, the original compensatory response no longer exists, and the pathophysiological changes are more complex, and the clinical manifestations may be atypical. Therefore, a preliminary diagnosis should be made by carefully asking about the medical history and analyzing the results of blood gas analysis. Mixed acid-base disorders can have many combinations, but it is obviously impossible for respiratory acidosis and respiratory alkalosis to occur together. When two primary disorders cause pH to change in the same direction, the deviation of pH from normal is more significant. For example, the pH value of patients with metabolic acidosis and respiratory acidosis is lower than that of a single disorder. When two disorders cause pH to change in opposite directions, the plasma pH value depends on the dominant disorder, and its fluctuation range is not as large as that of a single disorder because it is offset by the other disorder. If the opposite changes in pH caused by the two disorders just offset each other, the patient's plasma pH value can be normal, such as metabolic acidosis combined with respiratory alkalosis.