Final answer:
When a patient develops urticaria during a blood transfusion, the nurse must immediately stop the infusion, check the patient's vitals, and notify the physician for further management of the potential transfusion reaction.
Step-by-step explanation:
The first action a nurse should take when a client develops urticaria 30 minutes after a blood transfusion began is to stop the infusion immediately. Stopping the transfusion is critical because urticaria can be an early sign of a transfusion reaction, which can potentially lead to more severe symptoms such as anaphylaxis. After stopping the infusion, the nurse should then check the patient's vital signs to assess for further deterioration and then notify the physician. Depending on the severity of the reaction and physician's orders, medical intervention such as administering antihistamines, corticosteroids, or epinephrine may be needed to manage the patient's symptoms.