TSBL-Based Versus BMI-Based Biliopancreatic Limb Length in One-Anastomosis Gastric Bypass

TSBL-Based Versus BMI-Based Biliopancreatic Limb Length in One-Anastomosis Gastric Bypass: Interim Results of a Randomized Trial

This study compares two surgical techniques used during one-anastomosis gastric bypass (OAGB) surgery for patients with severe obesity. During this operation, surgeons create a bypass of part of the small intestine, and the length of this bypassed segment (called the biliopancreatic limb) affects both weight loss and the risk of nutritional side effects. In this trial, one group of patients has the limb length calculated individually based on the measured total length of their small intestine (TSBL-based method), while the other group receives a limb length based on standard body mass index (BMI) categories (BMI-based method). The study compares weight loss outcomes, improvement of obesity-related health problems, and complication rates between the two approaches over 12 months after surgery. The trial is being conducted at a single center in Almaty, Kazakhstan, and plans to enroll 100 patients total; this record reflects an interim analysis based on the first 75 patients enrolled.

This is a single-center, prospective, randomized controlled trial comparing two methods for determining biliopancreatic limb length (BPLL) during laparoscopic one-anastomosis gastric bypass (OAGB) in patients with morbid obesity. Eligible patients aged 18-65 years with BMI ≥35 kg/m² (non-Asian) or ≥32.5 kg/m² (Asian populations) who were candidates for primary OAGB were randomized 1:1 using a computer-generated randomization sequence with sequentially numbered, opaque sealed envelopes.

In the intervention (TSBL-based) group, total small bowel length (TSBL) was measured intraoperatively from the ligament of Treitz to the ileocecal valve, and BPLL was calculated as 0.35 × TSBL. In the control (BMI-based) group, BPLL was determined using standard fixed lengths based on BMI category (150 cm, 180 cm, or 200 cm). All other surgical steps were identical between groups.

The primary outcome is percentage excess weight loss (%EWL) assessed longitudinally at baseline, 3, 6, and 12 months. Secondary outcomes include percentage total weight loss (%TWL), BMI, BMI loss, improvement of obesity-related comorbidities, and postoperative complications graded using the Clavien-Dindo classification. Statistical analysis uses linear mixed models to evaluate effects of group, time, and group-by-time interaction.

Because blinding of patients and surgeons was not feasible given the nature of the surgical intervention, outcome assessment relied on objective anthropometric and clinical measures. This record reflects a planned interim analysis conducted on the first 75 of a planned total of 100 enrolled patients, with 51 patients having completed 12-month follow-up at the time of this analysis.

Inclusion Criteria:

• Age between 18 and 65 years
• BMI ≥35 kg/m² in non-Asian populations or ≥32.5 kg/m² in Asian populations
• Presence or absence of metabolic comorbidities (including type 2 diabetes, hypertension, and dyslipidaemia)
• Eligibility for primary one-anastomosis gastric bypass (OAGB)
• Provision of written informed consent

Exclusion Criteria:

• BMI below the defined thresholds
• Severe decompensated cardiac, pulmonary, hepatic, or renal disease
• Acute inflammatory conditions
• Active gastric or duodenal ulcer
• Psychiatric disorders or substance abuse
• Pregnancy or breastfeeding
• Active malignancy
• Severe intra-abdominal adhesions due to prior surgery
• Secondary obesity related to hypothalamic-pituitary-adrenal axis disorders