ABSTRACT
Mixed acid-base disorders are defined as the simultaneous presence of two or more primary disorders. Identification of these disorders hinges upon a knowledge of the normal secondary responses to single acid-base disturbances, defined by experimental observations in humans and animals (see Chapter 28). Most mixed disturbances are identified by an abnormal secondary response to the primary disturbance. For example a patient with metabolic alkalosis due to vomiting, who also has a primary respiratory acid-base disorder, will have a PaCO2 that is either higher or lower than the expected secondary response to metabolic alkalosis, and the level may even be below normal if a respiratory alkalosis is present. The effect of two or more disorders on arterial blood pH depends on the nature and severity of each disturbance. The resultant pH may be normal or near normal if the two disorders counterbalance each other or highly abnormal if the effect is additive.
