Final answer:
Treatment success after administering 1L of 0.9% sodium chloride for fluid volume deficit in a postoperative patient is indicated by an increased blood pressure, reflecting restored blood volume.
Step-by-step explanation:
The question is asking what change indicates treatment success after administering 1L of 0.9% sodium chloride to a postoperative client with fluid volume deficit. The correct answer is an increased blood pressure. When a patient has a fluid volume deficit, the blood pressure can be lower than normal because there isn't enough fluid in the bloodstream. After receiving a saline solution, which is isotonic and helps to replenish lost fluids without causing shifts in fluid concentration, the blood volume and, consequently, the blood pressure should increase. This is a positive indication that the fluid therapy is effective.