A client in the emergency department reports that he has been vomiting excessively for the last 2 days. His arterial blood gas (ABG) analysis shows a pH of 7.50, the partial pressure of arterial carbon dioxide (PaCO2) of 43 mm Hg, partial pressure of arterial oxygen (PaO2) of 75 mm Hg, and bicarbonate (HCO3) of 42 mEq/L. Based on these findings, the nurse documents that the client is experiencing which type of acid-base imbalance?