One-anastomosis gastric bypass is an attractive option in the armament of a Bariatric surgeon. A relatively simple procedure, it has been effective in inducing weight loss and resolution of obesity-associated comorbidities. Easy technique, shorter operative times, and low complication rates make it an attractive alternative option, particularly in super-obese individuals. While concerns remain regarding the long-term safety profile with regards to biliary reflux, risk of esophagogastric malignancies, and marginal ulcer. For the scope of this chapter, our focus will be on the advent of the concept, the surgical technique, and tips and tricks.

Introduction

The concept of “loop” gastric bypass was first introduced by Mason in 1967, which consisted of a gastric bypass with only one anastomosis [1]. Mason’s suggested a short and horizontal-shaped wide gastric pouch. This configuration exposed the esophageal mucosa to caustic bile reflux from the jejunal loop. Due to its bile reflux-inducing mechanism, this concept was abandoned quickly. Rutledge in 1997, introduced his version of one anastomosis gastric bypass naming it “mini-gastric bypass” (MGB). This was mainly because the original technique was described through a mini-laparotomy [2]. In his technique, the gastric pouch was a lesser curvature-based long sleeve starting 2–3 cm distal to the crow’s feet and extending slightly to the left of the “angle of His” proximally. A single ante-colic anastomosis between the gastric pouch and jejunum, about 3–5 cm wide was constructed 180–220 cm distal to the ligament of Treitz. This distance from the ligament of Treitz was modified marginally in selected cases based on the obesity class, age, and dietary preferences.

In order to reduce bile reflux, in 2002 Carbajo and Caballero proposed a variation to this technique wherein a latero-lateral anastomosis was performed between the gastric pouch and jejunal loop, averagely 250–350 cm from the ligament of Treitz. They named the technique “one anastomosis gastric bypass” (OAGB) or “bypass gastrico de una anastomosis” in Spanish (BAGUA) [3].

Over the years a variety of names like “omega loop gastric bypass” (OLGB) or “single anastomosis gastric bypass” (SAGB) have been used to describe the procedure [4, 5]. Finally, in 2013, a group of surgeons proposed the term “mini-gastric bypass-one anastomosis gastric bypass” (MGB-OAGB) to standardize the nomenclature and reduced the confusion created by multiple names for essentially the same procedure [6]. This nomenclature was later approved by the International Federation for the Surgery of Obesity and Metabolic disorders (IFSO) MGB-OAGB task force and recommended that OAGB should be the identifier for this procedure in future publications [7]. Over the last decade, although the popularity of the procedure is on the rise particularly in Asia Pacific and Europe region, [8] concerns regarding the possibility of bilio-enteric reflux and its long-term implications mainly the theoretical risk of gastric and esophageal cancer persists.

Indications

Suitability for bariatric surgery is based on body mass index (BMI) and the presence of comorbidity. These indications remain the same for offering OAGB

  • BMI of 40 kg/m2 or greater without coexisting medical problems.

  • Patients with a BMI greater than or equal to 35 kg/m2 and one or more obesity-related comorbidities, e.g., type 2 diabetes, hypertension, severe debilitating arthritis, hyperlipidemia, obstructive sleep apnoea (OSA), nonalcoholic fatty liver disease (NAFLD), gastroesophageal reflux disease (GERD), etc.

  • Patients with BMI between 30 and 34.9 kg/m2 with recent onset type 2 diabetes or metabolic syndrome also may undergo weight loss surgery, although there is a lack of sufficient data to demonstrate long-term benefits in such patients [9, 10].

Contraindications

As OAGB is performed under general anesthesia, any contraindications for giving general anesthesia automatically is a contraindication to proceed with surgery. From a surgical perspective, there are no absolute contraindications to OAGB, although relative contraindications do exist. These are drug/alcohol dependency, unstable coronary artery disease, end-stage lung disorders, severe heart failure, patients receiving active cancer treatment, portal hypertension, Crohn’s disease, and impaired intellectual capacity which prevents the patient from understanding the long-term implications and postoperative care. Preoperative reflux has been found to have an increased risk with the development of postoperative bile reflux [11] and hence it is the author’s opinion that OAGB should be deferred in these groups of patients.

Preoperative Assessment and Work-Up

Patients should be evaluated by a multidisciplinary team comprising of surgeon, physician, psychologist/psychiatrist, and nutritionist. These teams should work in close collaboration with the general practitioners and community healthcare/social workers. A thorough preoperative psychological, nutritional, and medical evaluation including assessment of comorbidities and fitness for surgery should be done. Patient education with regards to the lifestyle changes they need to undergo, what to expect before, during, and after surgery, nutritional and psychological changes postsurgery is paramount. We routinely prescribe 2 weeks of low-calorie high protein diet preoperatively. This is particularly helpful to shrink the liver size and assist during the surgery with liver retraction.

Operative Technique

Operation theater layout—The patient is placed supine position with split leg (Fig. 1). In bariatric surgery securing patient to the operative table is of paramount importance with straps at mid-thigh levels, to both legs separately and foot support.

Fig. 1
An illustration of a patient lying down on the operating table with split legs. His stomach is exposed over surgical drapes. The surgeon stands between his legs. First assistant is on the right of the patient, another person is near the patient's head. Another assistant is on the left. Above the patient is a person in front of a machine.

Theater setup and patient position

Full size image

Test this preoperatively by placing patient in anti-Trendelenburg position before starting the surgery. Both the arms are tucked by the patient side. Compression stockings and pneumatic compression devices are applied to both legs until unless contraindicated. The surgeon stands in between the legs, camera operator on the right side, and another assistant on the left. Standard 5 trocars technique is used (Fig. 2). While techniques for performing various bariatric procedures have a reasonable amount of variation based upon surgeon preference and training, the objectives are relatively uniform.

Fig. 2
An illustration depicts the silhouette of a torso. There are five points illustrated. The one on top is labeled liver retractor. One point is labeled 5 millimeters. The other three points have the label 12 millimeters.

Port placement

Full size image

Instrumentation—Over the years with advances in instrument technology many types of nontraumatic bowel graspers, energy devices, needle holders, suturing devices, liver retractors, suction-irrigation devices and tools designed for dissecting the abdominal cavity have been developed. Based on surgeon preference these can vary, important factor when using any device or instrument is its safety profile, simplicity of use, cost, easy availability, and reusability.

Abdominal access and technique—Creation of pneumoperitoneum can be done using a Veress needle or by direct trocar entry (Optical entry) and insufflating the abdomen to 12–15 mm of Hg. The table is then placed in anti-Trendelenburg position 30–40°. This allows better visualization of the stomach and tissue spaces that need to be dissected. Rest trocars are placed under vision. A liver retraction device is placed through one of these port sites, usually substernal to expose the hiatal, stomach, and surrounding areas.

Always start by performing a general examination of the peritoneal cavity to exclude any other pathology, e.g., abdominal wall hernia, adhesions, etc.

Phase 1—The angle of His and fundal fat pad is identified. While some surgeons just delineate the fundal fat pad, others prefer to dissect off the same to expose the left crus of the diaphragm explicitly in order for optimal positional of the stapling device at this extremely critical location. Always look out for a hiatal hernia which is not an uncommon occurrence in morbidly obese. If present, dissect the phreno-esophageal membrane and peri-esophageal adhesions to reduce the hernia. Post reduction, at least 2–3 cm of intra-abdominal length of esophagus should be achieved. Hiatal closure is performed using standard principles and care.

Phase 2—The most important step in OAGB is creation of a “long gastric pouch” to keep the bile stream as far away from the esophagus as possible. Identify the crow’s foot and just distal to it, dissect the gastro-hepatic omentum adjacent to the lesser curvature to enter the retro-gastric space. Care should be taken so that the entry point is always distal to the crow’s foot and proximal to the pylorus. Avoid unnecessary dissection medially along the lesser curvature posteriorly, so as to avoid injury to the left gastric artery. Based upon surgeon preference different stapling devices can be used. Using a 45 mm/3–4 mm stapler the first fire is performed from the right-side working trocar in a relatively perpendicular direction to the lesser curvature (Fig. 3). Any gastric pouch shorter than 9 cm has been correlated with an increased risk of postoperative duodeno-gastroesophageal reflux.

Fig. 3
Two photographs of the gastric region. The first image has an arrow that indicates, the point where we create retro-gastric window. The second image depicts a stapling device used at this point.

Identification of “crow’s feet” and first endo-stapler fire horizontally in distal gastric region perpendicular to the lesser curvature

Full size image

Lee et al. [12] long pouch also reduces the tension on the future anastomosis. At this moment the anesthetist passes a 36–40 Fr bougie under vision and narrow pouch is created over this. Vertical sectioning is next and using a 60 mm/3–4 mm stapler introduced through the left working trocar, fired from the crotch of the first fire parallel to the lesser curve and vertically up towards the angle of His. The endo-stapler is adjusted close to the bougie but not very tight. When in doubt ask the anesthetist to pull back the bougie by a few centimeters and reinsert to make sure it is not caught in the endo-stapler. After every staple fire, migratory staples if any should be removed. This reduces the risk of endo-stapler misfiring. Before every staple fire, check for posterior wall redundancy and do necessary adjustments. As you progress cranially towards the angle of His, posterior adhesions if any should be dissected. Once close to the angle of His, connection with the anterior dissection done at the onset is possible. Make sure to create a wide retro-gastric window so as to visualize the left crus of diaphragm. Stay well away “1–2 cm” lateral to the esophagogastric junction. This step is extremely critical to avoid complications namely leaks. Also, take care that the tip of the endo-stapler jaw does not injure the spleen or splenic vessels. Verify complete gastric transection, any terminal tissue connections do not hesitate to use an additional endo-staple fire. It is important to achieve hemostasis along the gastric staple lines on pouch as well as the remnant stomach, as these areas may become difficult to visualize once you perform gastro-jejunal anastomosis. A good gastric pouch should be long (15–18 cm), narrow, well vascularized without any torsion. It should be easy to bring the pouch caudally without any undue tension (Fig. 4).

Fig. 4
A photograph of a gastric pouch. There are some gauges on the site of operation. Three surgical devices are also depicted in the picture.

Tension-free long gastric pouch

Full size image

Phase 2—Reduce the anti-Trendelenburg tilt and if required we can do a slight Trendelenburg so as to help visualize and measure entire small bowel. The first step is to visualize the ligament of Treitz, which is achieved by lifting the gastro-colic omentum above the transverse colon. Jejunal counting is done with atraumatic bowel graspers, sequentially by grasping and running segments in increments of 5–10 cm. Once we reach a point of 150–200 cm distally, the assistant grasps the bowel as an indicator. The point varies based upon the patient’s obesity class, BMI, and comorbidities profile. In certain specific scenarios, this point may be extended beyond 200 cm. Although longer limb lengths can give better weight loss results, it also increases the risk of malnutrition and excess weight loss, especially beyond 250 cm [11, 13]. It is the author’s preference to continue running the bowel distally to count the entire small bowel upto the ileocecal junction, so as to assess the common channel (CC) length. Maintaining at least 300–350 cm of common channel is a prudent strategy.

Once the measurement is complete the assistant grasps the small bowel and holds it in place. Based upon surgeon preference if needed we can put a serosal stitch with vicryl keeping long ends or encircle the small bowel by a soft rubber drain (e.g., Jaques catheter) through a small opening in the mesentery. The assistant grasps the drain or vicryl stitch ends which helps in fixing the point as well as helps in providing traction during the gastro-jejunal (GJ) anastomosis. If any difficulty or tension while bringing the small bowel loop towards the gastric pouch should warrant an omental split.

Phase 3—Using an ultrasonic shear or a diathermy hook, small apertures are made in the distal gastric pouch and the small bowel (usually about 5 mm). Confirm that we have entered the lumen by passing a tip of nontraumatic bowel grasper into the lumen through the aperture or aspiration of intraluminal contents. Secure hemostasis and rule out any mechanical injury on the posterior or lateral wall. Using a 30 mm or 45 mm/3–4 mm stapler an ante-colic GJ anastomosis is performed. The gastro-enteric opening is then closed using 2–0 reabsorbable sutures or Stratafix or V-loc continuous closure. The authors prefer re-enforcing with a second sero-muscular layer (Two-layered technique). During learning curve, it may be advisable to perform the anastomosis over a gastric bougie by asking the anesthetist to pass the same distally into the efferent limb. The authors prefer performing a latero-lateral anastomosis so as to maintain an isoperistaltic pattern of food bolus flow (Fig. 5).

Fig. 5
Four photographs depict the steps of the surgery. The first image is probing the parts on the operation site. The second image illustrates dissecting. The third image depicts suturing. The last part is the end result of the anastomosis.

Steps of gastro-jejunal anastomosis

Full size image

Bile reflux is a major criticism of OAGB, and hence some surgeons prefer adding an “anti-reflux mechanism” wherein a continuous latero-lateral suture between the small bowel loop (along the antimesenteric border) and the staple line of gastric pouch performed. This should be done ideally before the GJ anastomosis is done

performed starting from between the junction of first and second vertical staple firing on the gastric pouch and 8–10 cm caudally up to the tip of gastric pouch as described in the “Spanish BAGUA technique” [14].

Phase 4—Competency of the anastomosis is tested using a leak test “methylene blue” or “pneumatic test” with help of the anesthetist. This can be done through a nasogastric tube or calibration tube respectively positioned just proximal to the anastomosis. Visualize all the staple lines and potential sites for bleeding and secure hemostasis using titanium clips. We routinely do not place intra-abdominal drain. All trocars are removed under vision to rule out any port site bleeding.

Postoperative Care

As per the ERAS protocol (Early recovery after surgery), adequate analgesics and anti-emetics are prescribed. Early mobilization and free fluids (clear liquid diet) starting initially with 20–30 ml swallows of water are recommended once patient is fully awake. Most patients usually tolerate this regimen well and are discharged 24h postoperatively with specific advice on diet, physical activity, medications, and red flag signs. We routinely discharge patients with anti-thrombotic prophylaxis (also given during hospital stay) based on the hospital recommendations. The bariatric team is always contactable by telephone for consultation if needed and there is a very low threshold to call the patient back for evaluation if any issues.

Complications

Although there is paucity of evidence from randomised control trials, early and late complication rates following OAGB are acceptable and comparable [7]. Complications such as staple line bleeding, anastomotic leak, stricture, marginal ulcer, surgical site infections, port site hernia, conversion rates, diarrhoea, dumping syndrome etc are similar to any other bariatric procedure. Risk of internal hernia is lower in OAGB compared to RYGB, as also is the occurrence of small bowel obstruction. Inadequate weight loss is relatively uncommon in OAGB [12]. This is mainly due to the greater effect of malabsorption, which may be a favourable effect in super-obese. The same may also lead to theoretically higher risk of nutritional deficiencies. There is lack of long-term data with regards to nutritional complications. Hence, lifelong follow up is paramount, and in the event of excessive weight loss or specific nutritional deficiency treatment with additional supplements is necessary. Unattended, risk of life-threatening malnutrition, Wernicke encephalopathy, iron deficiency anaemia and hypo-albuminemia is high. In cases where despite of active intervention excessive weight loss and deficiencies persists, reversal of OAGB to a RYGB or a sleeve gastrectomy is a valuable option. The two major criticism of OAGB are bile reflux and possible risk of cancer. Bile reflux – Overall incidence of bile reflux after OAGB is 1–4%, with a statistical correlation with pouches shorter than 9 cm and presence of pre-operative GERD [11]. In symptomatic reflux, the initial treatment consists of trial with probiotics e.g. yogurt, avoiding fatty and high-volume meals and proton-pump inhibitors (PPI). However, in severe and intractable cases, a reversal or revision to RYGB may be considered with a Roux-limb of 50 cm or more. Risk of cancer – Potential risk of gastric or esophageal cancer following OAGB is derived from the fact that exposure of GE junction and esophagus to alkaline bile reflux is a risk factor for Barrett’s esophagus. Till date only 4 cases of gastric cancer have been reported after loop gastric bypass (not OAGB), 3 of which were in the remnant stomach which are basically not related to OAGB. Only 1 case of cancer at gastric cardia following OAGB has been published. In conclusion definitive correlation of gastric cancer to OAGB has not yet been proven. The OAGB technique of Carbajo is an excellent modification to decrease or eliminate bile reflux after OAGB.

Conclusion

OAGB is one of the simpler bariatric procedure with a shorter learning curve and hence is an important addition to the armament of any bariatric surgeon. It provides durable weight loss and metabolic results with lower perioperative morbidity and hence holds promise for the future. Proper patient selection and standardization of technique are paramount so that in future OAGB forms an equivalent alternative to routinely performed bariatric and metabolic surgery.

Tips

  • Secure the patient well to the operating table, this allows us to maneuver the operating table to suit us when we operate in the supra or infra-colic compartments. Assess before scrubbing for the case.

  • Have a good team assisting during the surgery. A team well versed with the procedure reduces operative times and complications.

  • Do not hesitate to introduce additional trocars, struggling to reach the area of interest may lead to unnecessary complications.

  • Take care while manipulating the calibration tube or bougie, avoid any forceful intervention while inserting the same.

  • Always keep a long gastric pouch.

  • Always measure the entire bowel length namely the Biliopancreatic limb and the common channel. Maintain at least 300–350 cm of common channel.

Disclosure

Author’s institutional practice The primary bariatric procedure of choice in the institution of the author is a Roux Y Gastric bypass (RYGB) with the OAGB being reserved for patients with BMI > 55 or 60. However all patients are consented for a OAGB as a backup procedure if there are any technical factors that may hinder the safe performance of a RYGB. It is also to be noted that OAGB is an equally safe and effective procedure with frequently reported weight loss and co-morbidity resolution being better than a RYGB. However, in spite of being a simpler procedure, the author’s institution has dealt with complications related to troublesome gastric reflux, bile reflux, malabsorption and excess weight loss needing conversion to a RYGB. Internal hernias (Peterson’s hernia) although rare have been seen and dealt with in addition to rare twists seen with the long gastric pouch. These are to be borne in mind when the technique is adopted and advised to patients.