Final answer:
The effectiveness of a warm, moist compress for back pain relief is best indicated by a reduction in the client's pain. Indicators such as concentration, laughter, or stable vital signs are less direct. Intact skin without redness also signifies safe application.
Step-by-step explanation:
A nurse is caring for a client who is receiving a warm, moist compress to relieve lower back pain. The effectiveness of the compress can primarily be judged by the client's report of a decrease in pain or discomfort in the affected area. Options such as the client being able to concentrate while reading or laughing at a television show are not direct indicators of pain relief. Similarly, while normal vital signs are important, they do not specifically assess pain relief. The most direct indicator of the compress's effectiveness would be a report from the client that their pain has decreased. However, the presence of intact skin without redness on the lower back can be an indicator that the warm compress was applied safely and without causing additional harm or irritation to the skin.