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