The nurse appreciates the principal advantage in using patient-controlled analgesia (PCA) is that it:

The correct answer is D because patient-controlled analgesia (PCA) allows the patient to self-administer pain medication within preset limits, giving them a sense of control over their pain management, which can reduce anxiety. Choice A is incorrect because the nurse still needs to monitor the PCA settings and patient response. Choice B is incorrect because PCA aims to manage pain, not necessarily eliminate it completely. Choice C is incorrect as all medications carry some risk of adverse effects.