A nurse is caring for a client who has chronic kidney failure. The client's ABG values are pH 7.12 (7.35 to 7.45), HCO3 20 mEq/L (21 to 28 mEq/L), PaO2 90 mm Hg (80 to 100 mm Hg), and PaCO2 40 mm Hg (35 to 45 mm Hg). Which of the following acid-base imbalances should the nurse identify?