Q. A 70-year-old woman is brought to the emergency room with complaints of change in mental status for the past four days. Her caretaker at the nursing home where she resides told that she has had poor oral intake for the last 9 days. Her medical history is significant for ischemic heart disease and hypertension. Her medications include hydrochlorothiazide and aspirin. She does not use alcohol, tobacco or illicit drugs. On physical examination, she is not oriented to time, place and person. She has dry mucous membranes, decreased skin turgor and orthostatic hypotension. Neurologic examination reveals no focal neurologic deficit. Initial laboratory tests show the following results: Serum Sodium 110 mEq/L Potassium 4.0 mEq/L BUN 65 mg/dL Creatinine 3.6 mg/dL The patient is at risk of which one of the following complications if her electrolytes are rapidly corrected?