BACKGROUND:Although patient-controlled analgesia for pain management after abdominal surgery is common, efforts to find alternative effective methods to control postoperative pain are continuing. The aim of this study was to compare postoperative pain levels following intermittent regional administration of bupivacaine via a catheter placed in the rectus sheath or subcutaneously at abdominal surgery through midline incisions. METHODS:Consecutive patients undergoing elective midline laparotomy were assigned randomly to a group with two catheters placed over the fascia (suprafascial group) before surgical wound closure or to a group with catheters placed between the two sheaths of each rectus muscle (interfascial group). Pain levels were determined every 12 h, both at rest and with movement, by means of a standard visual analogue scale (VAS) for 72 h after surgery. The amounts of administered opioid were recorded. RESULTS:Sixty patients were enrolled in the study (30 patients in each group).The median VAS score 36 h after surgery, both at rest and with movement, was significantly lower in the interfascial group than in the suprafascial group (P<0·050). Repeated-measures ANOVA also showed a significant difference in the postoperative VAS scores (P<0·007). The amount of self-administered morphine was significantly lower in the interfascial group, overall (P = 0·001) as well as on postoperative day 1 (P = 0·001) and day 2 (P = 0·016). Bowel sounds returned more quickly in the interfascial group (P = 0·040). CONCLUSION:Locoregional catheter administration of bupivacaine following midline laparotomy is more effective when the catheter is placed in the rectus sheath compared with suprafascial delivery. REGISTRATION NUMBER:IRCT138810142982N1 (http://www.irct.ir).