Case: You are taking care of a 54 year-old man admitted to the ICU for acute SAH. The patient’s hospital course has been complicated by delayed cerebral ischemia despite appropriate medical management. This morning, labs show hyponatremia with normal a TSH, glucose, lipid panel, and potassium. The clinical question posed by your attending is how to differentiate cerebral salt wasting from SIADH. What is your response? HINT: the key is intravascular volume status! (Scroll Down For the Answer)