Final answer:
The principle used to encourage the nurse to monitor the patient's response to pain is Respect for autonomy.
Step-by-step explanation:
The principle used to encourage the nurse to monitor the patient's response to pain in the given scenario is Respect for autonomy. Respect for autonomy is the principle that states that patients have the right to make decisions about their own health care. By continually reviewing the pain management plan with the patient, the nurse ensures that the patient's priority of being as free of pain as possible is being met, and respects the patient's autonomy in managing their pain.