Differences in base case mean costs between the study cohorts for total postoperative ileus related costs ( hospital days , study drug , nasogastric tubes , postoperative ileus related concomitant medication and postoperative ileus related readmissions ) and total combined costs ( postoperative ileus related , laboratory , electrocardiograms , nonpostoperative ileus related concomitant medication and nonpostoperative ileus related readmission ) were evaluated by probabilistic sensitivity analysis using a bootstrap approach .