Study	Reason for exclusion
Abadir 2009	No placebo or sham control group for comparison
Dhanapal 2017	Surgical procedure was predominantly gastrectomy or gastrojejunostomy. Only 13 of 94 participants (14%) in the study underwent right hemicolectomy. No subgroup data available
Fry 1984	Surgical procedure was cholecystectomy, not colorectal resection
Gibbs 1988	Surgical incision was paramedian, not midline laparotomy
Nalda 1977	Intervention was epidural infusion of bupivacaine
NCT00557843	Trial withdrawn before enrolling any participants
NCT01062919	Control was epidural infusion of bupivacaine. Trial terminated due to low recruitment rate