A client whо hаs а histоry оf chronic obstructive pulmonаry disease (COPD) is admitted to the hospital with possible pneumonia. Respirations are shallow and breath sounds are diminished. Blood gases reveal: pH - 7.25 (normal level 7.35- 7.45), PCO2 - 70 (normal level 35-45), HCO3- 24 (normal level 22-26). What acid-base imbalance is this client experiencing?