Simple relationships that hold during compensation for metabolic or respiratory acid-base disturbances have been emphasized. When considered by the physician, they should allow for the interpretation and diagnosis of both simple and mixed disturbances. Since the correct diagnosis of an acid-base disturbance is central to initiation of correct therapy, these considerations are not merely academic exercises but are essential steps to follow in careful management. Table 6 summarizes the stepwise approach to diagnosis of an acid-base disorder. Application of these principles in a routine fashion combined with a careful history and physical examination often results in the successful diagnosis of complicated disturbances. Understanding of the pathophysiologic derangements in each specific disorder is necessary for full appreciation of acid-base balance in disease.