Final answer:
The most appropriate question to assess the duration of a client's back pain is "How long have you experienced this pain?" It provides a direct assessment of the time frame and chronology of the pain.
Step-by-step explanation:
To assess the duration of a client's chronic unrelieved back pain, the most appropriate assessment question that a nurse can ask is: "How long have you experienced this pain?" This question is directly aimed at establishing the time frame for when the pain started and how long it has persisted. It is a key element in pain assessment and helps in the determination of chronicity, potential causes, and the impact of pain on the patient's life.
The provided pain assessment tool, typically a numerical or visual analog scale such as the Mosby pain rating scale, is useful in quantifying the intensity of pain, but to obtain data on the duration, a direct timeline question is essential.
Regarding the other options, asking if the patient has had this pain before addresses history of pain rather than duration. Rating pain on a 1-10 scale assesses severity rather than duration, and asking when the pain began is similar, but it does not specifically inquire about the ongoing time span, which is crucial for understanding chronic pain.