1. 4th Department of Surgery, Attikon University Hospital, National and Kapodistrian University of Athens, 12462 Athens, Greece
2. Department of Hygiene, Epidemiology and Medical Statistics, Medical School, National and Kapodistrian University of Athens, 12462 Athens, Greece
3. 2nd Department of Anesthesiology, Attikon University Hospital, National and Kapodistrian University of Athens, 12462 Athens, Greece