Twenty-four hours after colon resection, urine output in a 70-year-old man is 10 mL/h. Blood chemistry analysis reveals sodium, 138 mEq/L; potassium, 6 mEq/L; chloride, 100 mEq/L; bicarbonate, 14 mEq/L. His metabolic abnormality is characterized by which of the following? 

A 55-year-old man with Crohn’s disease had undergone resection of small bowel and anastomosis. Ten days later, he is found to have bil- ious drainage of 1 L/d from the drains. He is started on total parenteral nutrition (TPN). Four days later, his arterial blood gases (ABGs) are pH, 7.25; PO2, 98 mm Hg; and PCO2, 40 mm Hg. His anion gap is 10. The most likely cause is which of the following? 

A 55-year-old man sustains numerous injuries involving the abdomen and lower extremities. During the intra- and postoperative periods, he is resuscitated with 10 L of Ringer’s lactate and 2 U of packed red blood cells (RBC). After initial improvement, he has severe dyspnea on the second postoperative day. The most useful initial diagnostic test is which of the following?