Final answer:
If a patient has a severe reaction to a blood transfusion, the nurse should discontinue the transfusion, administer oxygen, and administer diuretics if prescribed.
Step-by-step explanation:
If a patient has a severe reaction to a blood transfusion, there are several necessary actions for the nurse to take. Firstly, the nurse should discontinue the transfusion immediately to prevent further complications. Secondly, the nurse should administer oxygen to help the patient breathe and stabilize their condition. Lastly, the nurse should administer diuretics as prescribed, if ordered by the doctor, to help remove excess fluid and reduce the strain on the patient's cardiovascular system.