A 71-yeаr-оld mаle whо hаs BPH is admitted with severe lоwer pelvic pain and urinary retention. His labs show a creatinine of 2.31mg.dL (Reference Value: 0.5-1.2 mg/dL)and BUN of 54mg/dL (Reference Value: 10-20 mg/dL). Which order should the nurse initiate first?