This minimally invasive procedure involves creating a long, narrow tube from the stomach and connecting it directly to a loop of the small intestine, bypassing a large portion of the stomach and the first part of the small intestine. This design reduces the amount of food the stomach can hold and decreases the absorption of calories and nutrients, leading to weight loss.
This operation was first described in 2001 and it is currently the third most frequently performed bariatric worldwide after sleeve gastectomy and roux en y gastric bypass. It will likely over take roux en y gastric bypass in the future.
The one anastmosis gastric bypass OAGB is also referred to as mini gastric bypass or omega loop gastric bypass or single anastomsis gastric bypass. It is important to understand that the name mini gastric bypass is not because it is minor operation but rather because, when it was original described, part of the operation was done via a small or "mini" laparotomy (open mindline cut).
How does OAGB work?
OAGB induces weight loss through two primary mechanisms: restriction and metabolic changes. The surgical creation of a smaller stomach pouch limits the volume of food that can be consumed at one sitting, fostering an early sense of satiety. More profoundly, the procedure modifies the normal digestive process by allowing unaltered food to enter the intestine further along than it normally would. This triggers hormonal and receptor changes within the body, enhancing satiety, and optimizing energy utilization. In addition there is a small degree of fat malabsorption.
Benefits of OAGB
The benefits of OAGB extend beyond substantial weight loss. Patients often experience improvements in obesity-related conditions such as type 2 diabetes, hypertension, sleep apnea, and high cholesterol.
Typical Weight Loss Outcomes
Patients undergoing OAGB can expect to lose between 60% to 80% of their excess body weight within the first two years post-surgery. It's important to note that individual results may vary, and maintaining weight loss will require adherence to a healthy diet and regular physical activity.
Advantages of OAGB Over Sleeve Gastrectomy
Greater Weight Loss Potential: OAGB often results in a higher percentage of excess weight loss compared to Sleeve Gastrectomy, primarily due to its stronger metabolic effect than in sleeve gastrectomy.
Improvement in Metabolic Conditions: Patients undergoing OAGB may see a more significant improvement in obesity-related conditions such as type 2 diabetes, hypertension, and hyperlipidemia, attributed to the metabolic changes induced by the procedure.
Reversibility: Unlike the Sleeve Gastrectomy, which permanently removes a portion of the stomach, the OAGB is potentially reversible, offering more flexibility in managing long-term outcomes and complications.
Disadvantages of OAGB Over Sleeve Gastrectomy
Nutritional Deficiencies: OAGB carries a higher risk of nutritional deficiencies due to the malabsorption caused by bypassing a portion of the small intestine. This requires patients to commit to lifelong nutritional supplementation and monitoring.
Risk of Bile Reflux: There is a concern about the risk of bile reflux gastritis in OAGB patients, a condition where bile flows into the stomach, causing discomfort and potential damage to the stomach lining. This risk is less prevalent in Sleeve Gastrectomy since the pylorus is kept intact, regulating the entry of bile into the intestine.
Complexity of the Procedure: Although OAGB is considered less complex than traditional Roux-en-Y gastric bypass, it is still more complex than the Sleeve Gastrectomy.
Risk of Marginal Ulcer and Bowel Twist: Unique to gastric bypss, there is a risk of developing marginal ulcers at the site where the small intestine is connected to the stomach. Additionally, OAGB patients may experience a higher risk of bowel twist (intestinal obstruction) compared to those who undergo Sleeve Gastrectomy, which does not involve any alteration to the small intestine's routing.
Possible Dumping Syndrome: Gastric bypass patients might experience dumping syndrome, a condition characterized by rapid gastric emptying leading to symptoms like nausea, vomiting, diarrhea, dizziness, and sweating. This syndrome is more common in procedures that alter the normal flow of food through the gastrointestinal tract, including OAGB, but is less likely with Sleeve Gastrectomy.
Limitations on Endoscopic Procedures: After undergoing OAGB, as well as Roux-en-Y Gastric Bypass (RYGB),ERCP become nearly impossible due to the altered gastrointestinal anatomy. ERCP is a specialized endoscopy used to diagnose and treat conditions in the liver, gallbladder, bile ducts, and pancreas. The procedure involves the insertion of an endoscope through the mouth, down the stomach, and into the first part small intestine to reach the biliary and pancreatic ducts. After OAGB and RYGB, the bypassed proximal small bowel and the reconfiguration of the gastrointestinal tract prevent the standard approach to ERCP, complicating the management of biliary and pancreatic diseases.
Advantages of OAGB Over Roux-en-Y Gastric Bypass
Simpler Surgical Procedure: OAGB involves a less complex surgical technique with only one anastomosis (connection) between the stomach and the small intestine. This simplicity can lead to shorter operating times and potentially lower risks of surgical complications compared to the RYGB, which involves creating two anastomoses.
Faster Recovery and Shorter Hospital Stay: Due to its less invasive nature, patients undergoing OAGB often experience faster recovery times and may have shorter hospital stays compared to those who undergo RYGB.
Comparable or Superior Weight Loss Outcomes: Several studies have shown that OAGB can achieve comparable, if not superior, weight loss outcomes in the long term compared to RYGB.
Improvements in Metabolic Syndrome: OAGB has been effective in improving, and in some cases resolving, metabolic syndrome and its components, such as type 2 diabetes, hypertension, and hyperlipidemia. The metabolic benefits of OAGB can be attributed to the hormonal changes induced by the surgery, which are similar to or even greater than those seen with RYGB.
Potential for Reversal and Adjustability: Unlike RYGB, which is more challenging to reverse, OAGB offers the potential for reversibility and adjustability. This can be an essential advantage for patients who may require modifications to their initial surgery due to nutritional deficiencies or inadequate weight loss.
Lower Risk of Internal Hernias and bowel twist: The design of the OAGB procedure creates only one mesenteric defect, as opposed to the RYGB, which creates two mesenteric spaces due to its more complex intestinal rerouting. Internal hernias occur when intestines protrude through these mesenteric defects, a situation that can lead to serious complications requiring emergency surgery. The simpler configuration of OAGB minimizes the likelihood of such protrusions by limiting the potential spaces through which the intestines could herniate.
Disadvantages of OAGB Compared to RYGB
Risk of Bile Reflux: One of the primary concerns with OAGB is the increased risk of bile reflux gastritis. In OAGB, the rerouting of the digestive tract can allow bile to flow back into the stomach and esophagus, leading to inflammation, discomfort, and potential damage to the gastric and esophageal lining. This does not occur after RNYGB due to presence of the second joint.
Malnutrition and Nutritional Deficiencies: Although both operations alter nutrient absorption, the risk of malnutrition and nutritional deficiencies can be higher in OAGB patients. This is due to the more extensive bypass of the small intestine in OAGB, which affects the absorption of vitamins, minerals, and nutrients more significantly than RYGB.
Risk of Marginal Ulceration: Patients who undergo OAGB have an increased risk of developing marginal ulcers at the site where the stomach is connected to the small intestine. Although this is a risk with RYGB as well, the potential for ulcer formation may be higher in OAGB due to the large gastric pouch in OAGB producing more acid than the smaller pouch of RNYGB.
Variations in OAGB: The Length of the Biliopancreatic Limb
In performing OAGB, surgeons may opt for a "conservative" 150cm BP limb or a "standard" 200cm BP limb. Some centers might even extend the BP limb length to 250cm or more, based on their clinical judgment and the specific needs of the patient. This variation reflects the lack of consensus within the bariatric surgrey community regarding the optimal BP limb length for maximizing weight loss while minimizing complications. The choice of limb length often depends on factors such as the patient's Body Mass Index (BMI) or the total length of the alimentary limb, with some surgeons preferring longer lengths for individuals with a BMI over 50.
There is evidence that 150 cm BP limb might be the best choice for the following reasions:
Safe and effective in the medium term: This length has shown good results in terms of weight loss and improvement in comorbidities.
Not associated with a poorer weight loss outcome compared to the 200cm OAGB, even in patients with a BMI greater than 50.
Potentially lower risk of protein-calorie malnutrition and micronutrient/vitamin deficiencies: Longer BP limbs may increase the risk of these nutritional issues due to the greater extent of malabsorption.
