BackgroundConventional perioperative analgesic modalities (e.g. opioids, epidural analgesia) have their own drawbacks, which limit their clinical application. This study investigated the opioid-sparing effectsof the oblique subcostal transversus abdominis plane (OSTAP) blockade with ropivacaine for the patients undergoing open liver resection with a Mercedes incision.Methods126 patients who were scheduled for open liver resection were enrolled in this study. Patients were randomly assigned to receive bilateral ultrasound-guided OSTAPblocks with either 0.375% ropivacaine (groupT) or 0.9% isotonic saline (group C). Both groups also received intravenous patient-controlled analgesia and intravenous 40 mg parecoxib every 12 h for a total of 3 days. Preoperative and intraoperative parameters, plus intraoperative and postoperative cumulative sufentanil consumption, were recorded.Results70 patients were enrolled in the study finally. There were no significant differences between the two groups with respect to preoperative parameters, and surgical and anesthetic characteristics. The intraoperative sufentanil use, cumulative sufentanil consumption at 5 min after extubation, 2 h, 4 h,12 h and 24 h after operation in group T was significantly less than that in group C (P = 0.001, 0.001, 0.000, 0.000, 0.001 and 0.044, respectively). Compared with group C, postoperative NRS pain scores at rest were significantly lower at 2 h and 4 h postoperatively in group T (P = 0.04and 0.02, respectively); NRS scores at the time of coughing were also significantly lower in group T than in group C at all time points except 5 min after extubation (all P < 0.001). Furthermore, compared with group C, the number of intraoperative vasodilator use, the extubation time and the incidence of nausea was reduced in group T.ConclusionUltrasound-guided OSTAP block with ropivacaine can significantly decrease the perioperative cumulative dosage of analgesics and improve analgesic effect without obvious side effects for the patients who underwent an open liver resection with Mercedes incision when compared tothe ultrasound-guided OSTAP block with saline.Trial registrationThe study protocol was registered at http://www.chictr.org.cn (ChiCTR-TRC- 14004827) on February 19, 2014.