Paragastric Lesser Omentum Neural Block to Prevent Visceral Pain After Laparoscopic Sleeve Gastrectomy: A Randomized Clinical Trial Protocol.

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.