A 79-year-old woman is admitted for pneumonia. On day 3 of hospitalization, she becomes disoriented to place, demonstrates fluctuating levels of alertness, and shows difficulty sustaining attention. Her daughter states that although her mother has mild memory problems at home, she has never experienced this type of confusion. The nurse suspects delirium, but notes the presence of pre-existing mild Cognitive impairment. Which screening tool should the nurse prioritize to most accurately identify acute delirium in this client?