A 45-year old woman is admitted to the hospital following a head injury. She has severe polyuria (producing 1 L of urine every 2 hours) and polydipsia (drinking 3 to 4 glasses of water every hour).During a 24-hour period in the hospital, the woman produces 10 L of urine, containing no glucose. She is placed on overnight water restriction for fuher evaluation. The following morning, she is weak and confused. Her serum osmolarity is 330mOsm/L, her serum is 164 mEg/L, and her urine osmolarity is 70 mOsm/L. She is treated with dDAVP by nasal spray. Within 24 hours of initiating the treatment, her serum osmolarity is 295mOsm/L and her urine osmolarity is 620mOsm/L.