Final answer:
A medical power of attorney should make decisions based on the principle of autonomy, which gives patients the right to self-determination in their health care choices.
Step-by-step explanation:
A medical power of attorney should make a patient's decisions based on the principle of autonomy. The principle of autonomy states that patients have a right to exercise agency or self-determination when it comes to making decisions about their own health care. This means that the person appointed as a medical power of attorney should respect and honor the patient's wishes and preferences, acting as a proxy to make decisions that align with the patient's values and desires.