1. Department of Anesthesiology, Hitachi Ltd., Hitachinaka General Hospital, 20-1 Ishikawa-cho Hitachinaka-shi, Ibaraki 312-0057, Japan
2. Department of Gastroenterological Surgery, Ibaraki Seinan Medical Center Hospital, 2190 Sakai-mati Sasima-gun, Ibaraki, Japan
3. Department of Anesthesiology, Nippon Medical School, Sendagi 1-1-5, Bunkyo-ku, Tokyo 113-8603, Japan