Review Question - QID 217155

A 55-year-old woman is brought to the emergency department by her husband with a 1 hour history of an unremitting headache. The headache started suddenly while she was eating dinner and she says it feels like the “worst headache of my life.” An emergent CT scan of the head without contrast confirms the diagnosis, and a CT angiogram identifies the source of bleeding. The patient undergoes surgical management of her condition. On hospital day 3, she is found to be disoriented to person, place, and time. She also develops nausea and vomiting. Her medical problems consist of heart failure for which she takes furosemide, spironolactone, and metoprolol, which were continued at admission. Her temperature is 99.6°F (37.6°C), blood pressure is 100/60 mmHg, pulse is 112/min, and respirations are 16/min. Physical examination shows poor skin turgor. Capillary refill time is 4 seconds. Serum laboratory results are shown below:

Na+: 120 mEq/L
Cl-: 92 mEq/L
K+: 3.9 mEq/L
HCO3-: 26 mEq/L
BUN: 32 mg/dL
Creatinine: 1.0 mg/dL

Serum osmolality is 265 mEq/L and urine osmolality is 340 mEq/L. Urine sodium is 44 mEq/L. Which of the following is the most likely diagnosis?