Final answer:
The nurse should measure the client's urinary output first as a decrease in output can indicate a potential complication.
Step-by-step explanation:
The nurse should implement the action of measuring the urinary output first. A decrease in urinary output after a hysterectomy can indicate a potential complication, such as urinary retention or urinary tract infection. By measuring the urinary output, the nurse can assess if there is a decrease and take appropriate action.