Final answer:
The first intervention for a patient with a head injury and symptoms of high urine output and dry skin should be to assess the patient's level of consciousness, as it provides immediate information on their neurological status, which is critical for determining the urgency and nature of further interventions.
Step-by-step explanation:
A patient with a head injury presenting with symptoms of dry skin and an unusually high urine output of 600 mL/hr should prompt immediate nursing actions. Given the options presented, the most appropriate intervention to perform first is to assess the patient's level of consciousness. A change in consciousness is a critical sign of potentially serious brain injury or disease and warrants prompt assessment to determine the patient's neurological status.
While assessing urine specific gravity and notifying the physician are also important, these actions may follow the initial evaluation of consciousness if the patient is stable. Slowing the IV fluid infusion rate could be considered if overhydration is contributing to the excessive urine output, but it should be done under medical supervision and after other serious conditions have been ruled out.