Ketamine Recruiting Phase 4 Trials for Postoperative pain / Ileus; Mechanical / Constipation Drug Induced / Malignant Neoplasm of Colon / Ileus paralytic / Colon Diverticulosis / Rectum Neoplasm / Constipation / Ileus / Colonic Neoplasms / Rectum Cancer / Diverticulitis, Colonic Supportive Care