Monitoring for Complications of Hypernatremia

A patient with a history of diabetes insipidus has been readmitted to the hospital for electrolyte and fluid imbalances. The nurse notes that the patient has excessively high urine output and is demonstrating signs of dehydration, including increased thirst and a dry oral mucosa. Laboratory tests reveal a serum sodium level of 150 mEq/L and a serum osmolality of 310 mOsm/kg. Given the patient's clinical history and laboratory findings, which of the following assessments should the nurse prioritize to monitor for potential complications associated with hypernatremia?