Transmuscular quadratus lumborum (TQL) block for laparoscopic colorectal surgery: study protocol for a double-blind, prospective randomized placebo-controlled trial

Background: Thoracic epidural anesthesia is no longer considered the gold standard for perioperative analgesia in laparoscopic colorectal procedures. In the search for alternatives, the efficacy of the transverse abdominal plane (TAP) block and other abdominal wall blocks such as the transmuscular quadratus lumborum (TQL) block continues to be investigated for postoperative pain management. Most of the initial studies on TAP blocks reported positive effects; however, the amount of studies with negative outcomes is increasing, most probably due to the fact that the majority of abdominal wall blocks fail to mitigate visceral pain. The TQL block could prove attractive in the search for better postoperative pain relief after laparoscopic colorectal surgery. In several cadaveric studies of the TQL, a spread of dye into the thoracic paravertebral space, the intercostal spaces, and even the thoracic sympathetic trunk was reported. Given the advantage of possibly reaching the thoracic paravertebral space, the potential to reach nerves transmitting visceral pain, and the possible coverage of dermatomes T4-L1, we hypothesize that the TQL provides superior postoperative analgesia for laparoscopic colorectal surgery as compared to patient-controlled intravenous analgesia with morphine alone. Methods and design: In this prospective, randomized, double-blind controlled clinical trial, 150 patients undergoing laparoscopic colorectal surgery will be included. Patients will be randomly allocated to two different analgesic strategies: a bilateral TQL with 30 ml ropivacaine 0375% each on both sides, administered before induction of anesthesia, plus postoperative patient-controlled intravenous analgesia with morphine (TQL group, n = 75), or a bilateral TQL block with 30 ml saline each on both sides plus postoperative patient-controlled intravenous analgesia with morphine (placebo group, n = 75). Our primary outcome parameter will be the morphine consumption during the first 24 h postsurgery. Secondary endpoints include pain intensity as assessed with the numerical rating scale (NRS) for pain, time to return of intestinal function (defined as the time to first flatus and the time to the first postoperative intake of solid food), time to first mobilization, the incidence of postoperative nausea and vomiting during the first 24 h, length of stay on the post anesthesia care unit (PACU) and in the hospital, the extent of sensory block at two time points (admission to and discharge from the PACU), the doses of morphine IV as requested by the patient from the PCA pump, the total dosage of morphine administered IV, the need for and dose of rescue analgesics (ketamine, clonidine), free plasma ropivacaine levels after induction and at discharge from the PACU, and the incidence of adverse events during treatment (in particular, signs of local anesthetic systemic toxicity (LAST)). Epidural analgesia is no longer the standard of care for postoperative analgesia in laparoscopic colorectal surgery. Until now, the most effective analgesic strategy in these patients especially in an enhanced recovery program is still unknown. Several abdominal wall blocks (TAP, fascia transversalis plane block) are known to have an analgesic effect only on somatic pain. Recognizing the importance of procedure-specific pain management, we aim to investigate whether a transmuscular quadratus lumborum block delivers superior pain control in comparison to patient-controlled intravenous analgesia with morphine alone.