Final answer:
The nurse should provide clear instructions and reminders to communicate the change in basic care needs of the client.
Step-by-step explanation:
The nurse's action that best communicates the change in basic care needs for the client who is required to have nothing by mouth (NPO) for 8 hours prior to a test scheduled for tomorrow is to provide clear instructions and reminders. This can include explaining the importance of maintaining the NPO status, outlining the specific time frame in which the client should refrain from eating or drinking, and offering alternatives to manage hunger or thirst during this period.