Validity of the I‑FEED classification in assessing postoperative gastrointestinal impairment in patients undergoing elective lumbar spinal surgery with general anesthesia: a prospe... oleh Chun-Yu Wu, Chih-Jun Lai, Fu-Ren Xiao, Jen-Ting Yang, Shih-Hung Yang, Dar-Ming Lai, Fon-Yih Tsuang