The duration of the effect of autonomic neural blockade (ANB) is the most critical limitation for successful clinical application. The analgesic effect using only 0.5% bupivacaine may wear off after 12 to 18 hours. We have prolonged this effect using a combination of bupivacaine and dexamethasone. In this protocol, we aim to study three different local anesthetic combinations to prolong the effect of the ANB.

The study described herein is a prospective, double-blinded RCT involving patients undergoing laparoscopic sleeve gastrectomy (LSG) at Clínica Portoazul and Clínica Iberoamérica in Barranquilla, Colombia. The patients will be randomized to one of three parallel groups: ANB using 5% bupivacaine plus dexamethasone, 5% bupivacaine plus dexamethasone and a colloid, and 5% bupivacaine plus clonidine.

Patients All adult patients scheduled for LSG at each participating institution will be eligible for screening for study inclusion and granting of consent to study participation. The exclusion criteria will be the inability to perform an ANB because of anatomical difficulties, the need for revisional surgery, the need for concurrent surgical procedures beyond hiatal hernia repair, conversion to open surgical procedures, allergies to local anesthetics, and intraoperative complications (e.g., visceral or vascular perforations, or anesthesia-related complications requiring admission to intensive care).

Sample size The estimated sample size in each group was 50 patients ( total enrollment of 150 patients), assuming that for a balanced one-way ANOVA, using a sample size of 120 (each group: 40) would provide a statistical power of 0.9, with a significant level of 0.01 and a standard deviation of 3.

ANB The autonomic neural block is performed with a 25-gauge needle attached to a venous catheter extension introduced through the left 12-mm port. The needle is capped during its introduction, and the cap is removed inside the abdomen using a grasper and kept under direct vision. Infiltration of 20 mL of non-diluted 0.5% bupivacaine plus dexamethasone 8 mg, bupivacaine plus dexamethasone 8 mg plus a colloid 10 cc (Gelofusin, B. Braun Medical S.A) or bupivacaine 5% plus clonidine (0,150mgs) is performed at six levels with careful aspiration preceding fluid infiltration. After elevating the stomach with a grasper at the most proximal aspect of the lesser curvature and creating two windows at each side of the verticalized left gastric artery, two of the infiltrations are performed at t the base of the left gastric artery (Fig. 2). Four areas are infiltrated at the track of vagus nerves and branches. ANB is reinforced at the final stage of the procedure. When initial exposure of the celiac trunk proved difficult, elevating the sleeve can facilitate the procedure. The procedure is rapid, reproducible, and proven safe in a previous RCT. However, it has a learning curve. Details of the procedure are available.

Data collection An independent investigator will be responsible for collecting and recording the study data. Patients' age, sex, body mass index, current medications, and medical and surgical history will be recorded prospectively with informed consent at their visit to the preoperative clinic at the time of study enrollment. Details of the procedure will be consigned in the surgical record. An analog pain scale survey is administered by an investigator blinded to the patients' groups in person at one hour (in the recovery room), eight hours postoperatively the following morning, and by phone at 36 hours. The investigator recorded the need for analgesics and the presence of nausea, vomiting, and other symptoms at the same periods.

Statistical analysis Continuous outcome variables will be compared with two-sample t-tests. Categorical and binary outcome variables will be compared using chi-squared tests.

Analgesia protocol All patients received proton pump inhibitors, conventional antiemetics, and a scheduled baseline analgesic such as acetaminophen (1 g intravenously every six h) or dipyrone (1 g intravenously every six h). A nonsteroidal anti-inflammatory drug such as diclofenac and hyoscine butyl bromide (0.2 mg intravenously) is administered in non-allergic patients 12 14 hours post-surgery and the following morning if necessary. The rescue analgesic was Oxycodone (3 mg every 6 h). Oxycodone was the only opioid derivative used. After surgery, a popsicle was offered in the afternoon, and clear fluids were started the following day. Patients are discharged from the hospital in the afternoon the next day after surgery if they are hemodynamically within normal limits, tolerate clear fluids, and have controlled pain.

Inclusion Criteria:

All adult patients scheduled for Laparoscopic Sleeve Gastrectomy(LSG) at each participating institution will be eligible for screening for study inclusion and granting of consent to study participation.

Exclusion Criteria:

The exclusion criteria will be the inability to perform an ANB because of anatomical difficulties, the need for revisional surgery, the need for concomitant surgical procedures beyond hiatal hernia repair, conversion to open surgical procedures, allergies to local anesthetics, and intraoperative complications (e.g., visceral or vascular perforations, or anesthesia-related complications requiring admission to intensive care).

Randomization will be performed using sealed envelopes stratified by the institution in blocks of six. The data manager will prepare these envelopes. The data manager will store the randomization list containing the final treatment assignments. Only the data manager will have access to the randomization list throughout the study. These sealed envelopes will be placed in the patient's chart and will not be opened until the patient is in the operating room and general anesthesia has been initiated. The patient and the independent investigator assessing and recording the patient's data will be masked to treatment arm assignments.