71-year-old man was admitted to the hospital for al- tered mental status. His wife reported that the patient had become progressively confused and had been having visual hallucinations, seeing people and animals that were not really there. These symptoms started about 2 weeks before admission as intermittent episodes. She could not identify any triggering events or temporal pattern for these episodes. In the past 2 days, the patient's symptoms had become more persistent. She added that he had become in- creasingly forgetful in the past year but had had no prob- lem performing simple tasks or taking care of himself. This type of confusion had never occurred previously. The patient had a 12-year history of type 2 diabetes, had undergone coronary artery bypass 3 years previously, had symptomatic peripheral vascular insufficiency, and had stage V chronic kidney disease primarily due to diabetic nephropathy. For the past 10 months, he had been undergo- ing hemodialysis 3 times weekly for 3.5 hours each time via a left arm arteriovenous fistula. He had last undergone dialysis 3 days previously and was due for his scheduled dialysis on the day of admission. Two months before admission, the patient developed critical lower limb ischemia and a nonhealing left foot ul- cer. Multiple vascular interventions failed to restore suffi- cient limb blood flow; a month later, the patient underwent a transmetatarsal amputation. Postoperatively, he devel- oped surgical wound infection, necessitating repeated de- bridement and intravenous vancomycin administration. The patient's medications included stable doses of as- pirin, atenolol, atorvastatin, calcium acetate, insulin, gaba-