Q. A patient comes into the clinic reporting three days of stomach flu. She is feeling unsteady, and dizzy when she attempts to stand up, but has no episodes of full syncope. She has eaten very little the past few days due to nausea and frequent emesis. Blood tests reveal an arterial pH of 7.5 and a partial pressure of carbon dioxide of 53 mm Hg. What is the most likely etiology of this acid-base disturbance?