The Change in RetHe - Levels Perioperatively in a Cohort of Colorectal Surgery Patient

During a period of a year, reticulocyte hemoglobin content (RetHe) measurements (Sysmex) are done out of blood samples taken on several occasions during normal patient care: 1. preoperatively at the surgical or anesthetic outpatient visit 2. on admission or pre- induction of anesthesia 3. postoperatively at the postanesthetic care unit 4. on day 3 postoperatively 5. on day 5 postoperatively Additionally a Quality of Life (QoL) questionnaire will be taken from the participants before surgery and 30 days after surgery to evaluate the course of QoL perioperatively.