Background

In weight loss surgery, the concept of a “loop” gastric bypass consisting of one anastomosis was first introduced by Mason in 1967 [1]. In Mason’s configuration, the gastric pouch was wide and short, and had a horizontal shape, exposing the esophageal mucosa to caustic bile reflux coming from the jejunal loop. Because it was a reflux-inducing procedure, this bypass concept was quickly abandoned. In 1997, Rutledge introduced a different version of one anastomosis gastric bypass and named it “mini gastric bypass” (MGB) because the procedure initially was described through a “mini-laparotomy”, in analogy with “mini-laparotomy cholecystectomy”.

MGB consisted of a lesser curvature-based long-sleeved gastric pouch starting 2–3 cm below the level of the crow’s foot and extending proximally slightly to the left of the angle of His. An antecolic 3–5-cm-wide anastomosis was then constructed between the pouch and the jejunum, about 180–220 cm distal to Treitz’ ligament. In the super obese, the distance to Treitz’ ligament would be about 250 cm, in the elderly or vegetarians 180–200 cm and in type II diabetics without major obesity about 150 cm [2].

In 2002, Carbajo and Caballero (Spain) proposed a technical variation to prevent gastroesophageal (GE) bile reflux. They called their technique one anastomosis gastric bypass (OAGB) or in Spanish bypass gastrico de una anastomosis (BAGUA). According to this technique, OAGB had a latero-lateral anastomosis between the loop of jejunum and the pouch, and the distance to Treitz’ ligament averaged 250–350 cm [3].

Since then, other names such as “single anastomosis gastric bypass” (SAGB) or “omega loop gastric bypass” (OLGB) have been proposed to define the same technique [4, 5]. In 2013, the confusion created by the various names led a group of surgeons to use the name mini gastric bypass-one anastomosis gastric bypass (MGB-OAGB) to define this surgery [6].

Despite an increase in the utilisation of MGB-OAGB, particularly in Europe and the Asia Pacific regions [7], there remains concern that the MGB-OAGB could create bilio-enteric reflux, and may increase the risk of esophageal and gastric cancer.

The task force undertook a systematic review to summarise the current evidence on the efficacy and safety of these procedures with the aim of providing the most up-to-date information to guide practice.

Methods

Literature Search

We performed a comprehensive literature search to identify studies reporting any experience or outcomes with the MGB-OAGB. The search was done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. We searched MEDLINE (1946 to November 2017), EMBASE (1974 to November 2017), PubMed (until November 2017) and the Cochrane Library (until November 2017). Search terms were broad, to encompass all mini gastric bypass procedures (MGB). These include terms specifying the bariatric procedure (gastric bypass, mini gastric bypass, one anastomosis gastric bypass, bariatric surgery), single anastomosis (single anastomosis, loop anastomosis, one anastomosis, omega loop, mini). A full list of search terms is presented in Appendix Table 4. Manual searching of reference lists from reviews, as well as references from selected primary studies, was performed to identify any additional studies.

Inclusion Criteria

Studies were selected that reported on outcomes after single anastomosis gastric bypass procedures. All study designs were accepted. We summarised data for studies with greater than 15 participants, and with greater than 1-year follow-up; however, studies of all sizes and follow-up time frames were collected. Only full text articles were included.

Data Extraction

Information extracted from eligible studies included basic study data (year, country, design, study size), demographic data, surgical technique, follow-up, weight loss, evolution of co-morbidities and complications.

Results

Literature Search

Using the search strategy described, we identified 3936 studies. After 877 duplicates were removed, we screened titles and abstracts for 3059 records. Full text articles for 255 eligible studies were screened, and 168 articles were subsequently excluded. Hence, 87 full length publications were identified for inclusion.

Of these studies, 78 focused on outcomes of OAGB. Only 52 of these studies had reasonable follow-up and study numbers, with 26 having less than 1 year follow-up [8,9,10,11,12,13,14,15,16,17,18,19,20,21,22] or ≤ 15 OAGB patients [23,24,25,26,27,28,29,30,31,32,33]. A further nine studies focused on complications following OAGB (Fig. 1).

Fig. 1
figure 1

PRISMA flowchart

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Overall Summary

A total of 52 reasonable quality (n > 15, follow-up > 1 year) studies were identified. Of these, there were 16,546 patients (excluding 2 studies with significant overlap in patient cohort), with a median of 94.5 (IQR 34.5–203, range 16–2678) patients per study. The average study body mass index (BMI) ranged from 25.3 to 67 kg/m2, with a mean study BMI of 44.6 ± 6.4 kg/m2.

Over a range of follow-up times, the average excess weight loss was 74.8 ± 12.0%. In studies that reported diabetes remission, there was observed resolution of diabetes in 2495 of 2855 diabetic patients (87.4%).

Outcomes from MGB-OAGB

There are currently 4 randomised controlled trials, 34 single-arm cohort studies and 14 multiple-arm comparison cohort studies on MGB-OAGB, which are summarised in Table 1. Sixteen studies reported on just primary MGB-OAGB procedures, 6 on revision operations, 15 analysed a mix of both and 15 did not state whether they were primary or revision operations.

Table 1 Study data
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MGB-OAGB as a Primary Procedure

In total, there are 191 patients who have been enrolled in 4 RCT and a further 8724 patients reported up in retrospective and prospective cohort studies. This number is likely to be an overestimation due to shared patients in multiple series.

Weight Loss

In the four randomised controlled trials, weight loss was reported at 12 months (EWL 66.9 ± 23.7% [35] and EWL 66.9 ± 10.9% [37]), 2 years (EWL 64.4 ± 8.8% [34]) and 5 years (TBWL 22.8 ± 5.9% [36]). Of note, in the Lee trial comparing MGB-OAGB to SG at 5 years, the mean starting BMI was substantially lower than the other trials at 30.2 ± 2.2 and the EWL achieved was over 100% with a mean finishing BMI of 23.3 ± 2.2 kg/m2. These results were not significantly different to comparator operations.

In the prospective cohort studies, weight loss at 12 months was EWL 80.5% (n = 2410; follow-up not reported) [38], EWL 70.1 ± 8.4% (n = 838; 94.8% follow-up) [51] and EWL 70 ± 20% (n = 89; 100% follow-up) [52]; 23 months 68.4% (n = 126; 45.2% follow-up) [20]; 3 years EWL 81.5 ± 5.0% (n = 570; 89.4% follow-up) [51]; 5 years EWL 72.9% (n = 1163; 56% follow-up) [44] and 77.0 ± 5.1 (n = 254; 79.1% follow-up). Two other prospective studies were not included as they failed to differentiate primary or secondary procedures and did not accurately report weight loss as the focus of these papers was health change rather than weight loss [53, 55]. Weight loss reported in the retrospective cohort studies was similar (Table 1).

Change in T2DM Management

Diabetes or metabolic syndrome was reported upon as a co-morbidity of interest in all 4 RCT. In the Lee trial comparing MGB-OAGB to RYGB, there was 100% resolution of the metabolic syndrome at 2 years [34]. No other treatment for T2DM was required at 12 months for 50% of participants with T2DM in-trial (n = 2) [35] and 84% (n = 49) [37]. At 5 years, 60% of participants with T2DM at baseline had a HbA1c < 6.5% without medications in the low BMI trial focusing on change in diabetes [36]. Again, these results were not significantly different to the comparator populations.

There are six prospective cohort studies that addressed change in diabetes status following MGB-OAGB. The change in T2DM management was reported in various ways, but all reported major improvement (Table 1).

Complications

There was one early death in-trial reported in the four RCT (3.3% death rate for that trial [36]; 0.05% for pooled data). A further 15 deaths were reported in the prospective and retrospective cohort studies giving a crude death rate overall of 0.17%. This is likely to be an underestimation due to shared patients between reports.

Early complications were experienced by 17/191 (8.9%) patients in the RCT cohort with 3 patients requiring a return to theatre (1.5%). This is likely to be an underestimation as minor complications were not reported by Darabi [35] and no complications other than the death were reported by Lee [36]. The early complication rate reported in the retrospective and prospective cohort studies was again similar (Table 1). Early complications included anastomotic leak, wound infection, haemorrhage, anastomotic stricture and organ perforation (Table 2).

Table 2 Studies focusing on complications
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There were no late deaths in the RCT cohort, and four in the cohort studies. Late complications included marginal ulcers, bowel obstruction, malnutrition and gastroesophageal reflux including biliary reflux.

MGB-OAGB as a Secondary Procedure

There is one prospective cohort comparator study, one retrospective cohort comparator study and four retrospective studies specifically addressing the use of MGB-OAGB as a revisional procedure with a total of 222 patients enrolled in these 6 studies.

Weight loss overall at each time-point appears to be lower than in the primary procedures, although one retrospective cohort study with a follow up rate of 91% (n = 30) did achieve EWL 66 ± 22% at 5 years [81].

Change in T2DM management was only reported in one retrospective cohort study (n = 30). There were seven patients with T2DM at baseline and at 5 years six patients required no treatment other than surgery for their T2DM giving an 85% resolution rate [81].

One early death has been reported with an in-trial death rate of 3.4% [79] and an overall death rate in these studies of 0.45%. No late deaths have been reported.

Early complication rates range from 2.6 to 21.6%. The wide variation probably reflects differences in reporting. Early complications include anastomotic leak, haemorrhage, anastomotic stricture and organ perforation.

Late complication rates are only reported in two studies (6.6% [81] and 8.1% [83]). They include gastroesophageal reflux disease (bile reflux not specifically reported) and bowel obstruction.

Operative Technique for MGB-OAGB

Operative technique (Table 3) varied among groups in various domains—pouch and bougie size, gastrojejunostomy anastomosis technique, limb length.

Table 3 Operative technique
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Pouch and Bougie Size

The description of the starting point for gastric stapling varied; however, most groups started at the level or just below the Crow’s foot on the lesser curve. The majority of studies used a 36 French bougie; however, the bougie size varied from a 1 cm diameter nasogastric tube to a 42 French bougie.

Gastrojejunostomy

A linear stapler was used in most cases, varying in length from 30 to 60 mm. Only a partial length of the stapler was used in some cases, creating an anastomosis as small as 1.5 cm. Handsewn anastomoses were not commonly used (described in one study).

Limb Length

The most common limb length used was 200 cm, reported by 27 studies. Nine studies reported forming limbs < 200 cm, five reported > 200 cm and five reported the “Rutledge” technique but no length. Ten studies tailored the limb length according to pre-operative body mass index (BMI).

Discussion

The current evidence suggests that MGB-OAGB provides effective weight loss that is durable to 5 years. Weight loss appears to be more effective in primary operations when compared to revisional procedures; however, small numbers limit our ability to completely assess this parameter.

MGB-OAGB appears to have a favourable effect on T2DM, although numbers in the reports are small, and durability of glycaemic effect has not been reported.

There is an acceptable early and late complication rate, and the rates of symptomatic bile reflux are lower than first feared. Complication rates appear to be higher in the revisional setting. There is a lack of long-term nutritional information and rates of bile reflux rely mainly on self-reporting. These are areas of concern and it is imperative that patients who undergo these procedures understand the need for on-going care from their bariatric team.

The ideal operative technique has not been defined. The most common description commences the pouch below the crows-foot with a stapled anastomosis and 200 cm common limb length; however, there is a great deal of variance in each of these elements. This may be an important issue to be addressed by an RCT in the future.

There is a paucity of RCT evidence, with the majority of evidence coming from retrospective cohort studies. There is a need for well-designed large prospective cohort studies as well as RCT in to the future to better define where MGB-OAGB should be placed in the current suite of bariatric procedures.

The term mini gastric bypass/one anastomosis gastric bypass (MGB-OAGB) has been used throughout this position statement as this has been the agreed nomenclature endorsed by the Executive Board of IFSO. Whilst the initial use of the word “mini” reflected the minimally invasive approach used for the procedure compared to a laparotomy, there is a risk that the term will be misinterpreted as meaning the surgery itself is a lesser procedure—both in terms of surgical risk and metabolic benefit. The current systematic review reinforces that the procedure is effective in terms of weight loss and metabolic benefit, but also carries surgical risk that is very similar to RYGB. Therefore, the taskforce recommends that in the future the procedure be referred to as “one anastomosis gastric bypass (OAGB)”.

The need for more RCT’s is paramount to our understanding of our interventions; however, the need for guidance for emerging procedures is the responsibility of organisations, such as IFSO. Professional societies must continue to extrapolate the existing data against the needs of the patients we serve and the availability of current technology on a micro and macro level. Though position statements are not without bias, they are meant to be temporal in nature. Continued re-analysis is necessary in order to remain relevant.

Recommendation of the IFSO MGB-OAGB Taskforce

Based on the existing data, we recommend the following:

  1. 1.

    OAGB should be the identifier for this procedure in future publications.

  2. 2.

    Whilst early results are promising in terms of weight and T2DM management, there is a lack of long-term evidence for durability of effect as well as long-term nutritional complications. Bile reflux is either under reported or does not seem to be a major issue, but remains a theoretical risk. Patients should be encouraged to remain in long-term multidisciplinary care.

  3. 3.

    Patients undergoing OAGB in the revisional setting have less weight loss and more complications than with primary procedures.

  4. 4.

    Surgeons performing this, as well as any other bariatric/metabolic procedure, are encouraged to participate in a national or international registry so that long-term data may be more effectively identified.

  5. 5.

    OAGB is a recognised bariatric/metabolic procedure and should not be considered investigational.