Visceral pain (VP) following laparoscopic sleeve gastrectomy remains a substantial problem. VP is associated with autonomic symptoms, especially nausea and vomiting, and is unresponsive to traditional pain management algorithms aimed at alleviating somatic (incisional) pain. The present study was performed to evaluate the safety and effectiveness of laparoscopic paragastric autonomic neural blockade (PG-ANB) in managing the symptoms associated with VP following sleeve gastrectomy.

Introduction Although seldom discussed, visceral pain (VP) is the most significant source of pain in the first 24 hours following laparoscopic sleeve gastrectomy (LSG) and other laparoscopic procedures (1). The somatic pain induced by surgical trauma to the abdominal wall after LSG is effectively managed using conventional analgesia and transversus abdominis plane (TAP) blocks (2-4). In contrast, the visceral, colicky pain patients experience after LSG does not respond well to traditional pain management regimens. During the last 15 years at our institutions, we have used many analgesic strategies to manage these burdensome symptoms in more than 2000 LSG procedures. Despite these efforts, no analgesic strategies have been satisfactorily effective (5,8,9).

Autonomic nerve blocks have been described in the pain management literature. Specifically, celiac ganglia blocks have been reported in managing chronic pain caused by foregut malignancies or pancreatitis (11,12). In these patients, neuraxial blocks have been demonstrated to be safe and effective methods of chronic pain management. To our knowledge, however, paragastric autonomic neural blockade (PG-ANB) has not been performed as part of perioperative multimodal pain management algorithms in gastrointestinal surgery. The two proposed main mechanisms of action of this autonomic blockade are a reduction in the parasympathetic influence over the stomach, which reverses its increased muscular tone and deactivates mechanosensitive receptors in the organ wall, and blockade of the afferent sympathetic fibers that convey VP to the spinal cord (13).

In a pilot observational study involving 35 patients, we observed improvement in the severity of VP in the epigastric and retrosternal areas as well as improvement in associated autonomic symptoms following PG-ANB (14). The effect was most pronounced during the immediate postoperative period but persisted until discharge. Analgesic requirements and the presence of nausea and vomiting were also reduced. The current study was performed to further validate these preliminary findings through a randomized, double-blinded controlled trial.

Study design This prospective, double-blinded, randomized clinical trial involved patients undergoing laparoscopic sleeve gastrectomy at two high-volume institutions. The patients were randomized to laparoscopic transversus abdominis plane block with or without PG-ANB.

Sample size Previously published data have indicated that differences of 1 to 2 points on an 11-point visual analog pain scale are clinically significant (15-17). Based on these prior studies, we chose a difference of 1 point as the minimum clinically significant difference for sample size calculation and assumed a standard deviation of 2 points. With a p-value of 0.05 and a power of 0.80, we estimated that a total of 128 patients would need to be enrolled in this study. To allow for any potential loss to follow-up, we enrolled 150 patients in the study.

Randomization and blinding Randomization was performed using sealed envelopes prepared by the data manager and stratified by institution in blocks of six. The data manager stored the randomization list containing the final treatment assignments. Only the data manager had access to the randomization list throughout the study. These sealed envelopes were placed in the patients' charts and could not be opened until the patient was in the operating room under general anesthesia. At that point, the surgeon became cognizant of the procedure to perform but did not participate in assessing the patient or collecting data. Both the patient and the investigator assessing the patient were blinded to the treatment arm assignments. The investigator evaluated the patients for vital signs, pain scores, autonomic symptoms, and analgesic requirements and recorded the information.

Data collection The patients' age, sex, body mass index, current medications, and medical and surgical history were prospectively recorded at the preoperative clinic visit during study enrollment with informed consent. An analog pain scale survey was administered by an investigator blinded to the patients' groups at 1 hour postoperatively (in the recovery room), 8 hours postoperatively, and the following morning. The investigator recorded the need for analgesics; the presence of nausea, vomiting, retching, excessive salivation, hiccups; and vital signs.

Statistical analysis Continuous outcome variables were compared with two-sample t-tests. Categorical and binary outcome variables were compared using chi-squared tests. Patient-reported pain scores were further compared using linear regression with the surgeon who operated and the location of the procedure as covariates to assess the effect of the surgeon and location on the primary outcome.

Postoperative recovery protocol All patients received proton pump inhibitors, conventional antiemetics, and a scheduled baseline analgesic such as acetaminophen (1 g intravenously every 6 hours) or dipyrone (1 g intravenously every 6 hours). The first-line rescue analgesic was a nonsteroidal anti-inflammatory drug such as diclofenac (intravenously every 12 hours) together with hyoscine butylbromide (0.2 mg intravenously every 12 hours), and the second-line rescue analgesic was tramadol (1 mg per ideal body weight intravenously every 6 hours). Tramadol was the only opioid derivative used. A popsicle was offered the afternoon after surgery, and clear fluids were started the following day. Patients were discharged from the hospital at noon the day after surgery.

Inclusion Criteria:

Adult patients who were scheduled for LSG at each participating institution from 25 August 2021 to 8 February 2022 and consented to study participation.

Exclusion Criteria:

• the exclusion criteria were an age of <18 years.
• the performance of concomitant procedures in addition to LSG.
• allergies to medications included in the postoperative management protocol.
• anesthetic complications related to the LSG that would alter the postoperative management protocol.
• surgical complications related to the LSG that would alter the postoperative management protocol.