Introduction

Since its inception in the mid-1950s, gastrointestinal surgery to treat excess adiposity and associated medical conditions has significantly changed [1]. Weight loss surgery, in its early history, lacked regulation, was associated with a high risk of adverse events, and had a high rate of recurrent weight gain (RWG). There were no uniform guidelines for patient selection, preoperative work-up, procedure selection, and long-term follow-up. These deficiencies contributed to the high rates of suboptimal outcomes.

To create uniform criteria for bariatric surgery, in 1991, the National Institute of Health (NIH) in the USA held a consensus conference on gastrointestinal (GI) surgery for the treatment of severe obesity [2]. A multidisciplinary panel of “experts” reviewed the available peer-reviewed literature and patient experience and created the first criteria for the practice of metabolic bariatric surgery (MBS). However, since 1991, there have been dramatic changes in the field of MBS, including fellowship training, accreditation of MBS centers of excellence, development of MBS registries, the introduction of minimally invasive surgery, and new procedures such as sleeve gastrectomy (SG), and dramatic improvements in perioperative and long-term patient care and safety. Despite these improvements in surgical techniques and perioperative care for patients undergoing MBS, the reliance on the 1991 NIH criteria for determining patient candidacy for surgery remained unchanged, and surprisingly, it is still in wide use more than 33 years later.

In 2022, a group of metabolic bariatric surgeons and other clinicians caring for people with obesity recognized that the 33-year-old guidelines based on expert opinion in the era of open surgery did not reflect the current published literature or state of the field. There was a growing interest in revisiting the 1991 NIH criteria and revising it to reflect MBS’s current practice.

The two largest MBS organizations in the world, the American Society for Metabolic and Bariatric Surgery (ASMBS) and the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO), agreed to partner to create new guidelines that would be evidence-based and rely on the most up to date high quality published literature along with current expert global practice. The group searched the literature for high-level evidence using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [3]. Without supportive literature, a Delphi survey of experts in the field was performed [4]. Systematic reviews were performed on 13 topics highlighted in the recently published MBS guidelines. This study aimed to determine the level of evidence and the grade of the recommendations of these 13 previously published criteria [5, 6]. Tables 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and 13

Table 1 MBS Indications for Individuals with BMI 30-34.9
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Table 2 IFSO/ASMBS Delphi Results of MBS indications individuals with class II obesity with no associated medical problems
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Table 3 BMI thresholds in the Asian population for MBS
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Table 4 MBS in the older population
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Table 5 MBS for the pediatrics and adolescents
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Table 6 MBS prior to joint arthroplasty (as a bridge)
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Table 7 MBS and abdominal wall hernia repair
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Table 8 MBS prior to organ transplantation
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Table 9 MBS for BMI ≥60 kg/m2
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Table 10 MBS in patients with liver cirrhosis
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Table 11 MBS in patients with heart failure
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Table 12 Multidisciplinary care
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Table 13 Revisional surgery
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Methods

In order to methodologically support the previously published ASMBS/IFSO guidelines, two international teams of writers were created.

One team of seven researchers (MDL, GM, AI, GP, ST, SC, AV) performed a systematic search of high-level evidence for different items, according to the PRISMA (see PRISMA Prospect). Two independent researchers analyzed each article, first by title and abstract and subsequently by the full text, and extracted the relevant data. In case of disagreement, a third researcher (MDL) was consulted.

Eventually, 12 different systematic reviews from the 13 PRISMA were carried out. PRISMA on item 2 (BMI 35–40 kg/m2 without obesity-associated medical problems) produced no studies.

The level of evidence and grade of recommendation are categorized in Table 14.

Table 14 Grade of recommendation and level of evidence
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The second team (MDL, MK, ST) was tasked to resolve any issues not answered by the systematic reviews. For these situations, a Delphi survey was constructed and consisted of two consecutive rounds. Forty-nine recognized MBS experts from 18 countries participated in this Delphi survey to address nine statements that did not have strong backing from the literature search (Table 2 and Table 15). Consensus was reached when the agreement/disagreement rate was equal to or greater than 70%. An online platform (Survey Monkey on https://www.surveymonkey.com/r/MBS-Criteria) was used. Seven statements reached consensus in the first round, and two reached consensus in the second round of voting (Table 2 and Table 15). Statements 1 to 5 referred to item 2 (body mass index [BMI] 35–40 kg/m2 without comorbidities), and statements 6 to 9 referred to item 6 (joint arthroplasty).

Table 15 IFSO/ASMBS delphi results on MBS in individuals need joint arthroplasty
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Results

BMI criteria for MBS

1. MBS for BMI 30–34.9 kg/m2 [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35]

PRISMA Appendix 1 [PubMed, Cochrane, Embase]

Systematic Review Table 1

Forty-three articles were included in the present review, 29 (69%) were conducted on non-Asian patients [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35] and 13 (31%) on Asian patients.

Nine retrospective (31%) and 20 (69%) prospective studies reported MBS results. All articles had a good/fair quality. Two articles investigated the effects of surgery on patients with BMI <30 kg/m2, four papers compared outcomes in low BMI with results in patients with severe obesity, and three other studies made a comparison with lifestyle intervention.

Seventeen articles reported results after Roux-en-Y gastric bypass (RYGB), 11 after SG, 1 after one anastomosis gastric bypass (OAGB), 2 after biliopancreatic diversion (BPD), 7 after adjustable gastric banding (AGB), and 2 after revisional surgery from AGB to RYGB with an overall medium follow-up of 29.3 [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120] months.

Operative time and length of stay (LOS) appeared comparable to available data in the literature for MBS in BMI ≥35 kg/m2. All articles reported satisfactory weight loss with no mortality. Clavien–Dindo complications grades 3–4 ranged from 0 to 40% (40% in a paper on BPD complications). A higher complication rate was reported after revisional surgery. Remission from type 2 diabetes mellitus (T2DM) and hypertension (HTN) ranged from 33 to 100% and from 28 to 100%, respectively.

Recommendation

  • MBS is recommended for patients with T2DM and a BMI of 30–34.9 kg/m2.

  • MBS is recommended for patients with a BMI of 30–34.9 kg/m2 and one obesity-associated medical problem.

  • MBS should be considered in patients with a BMI of 30–34.9 kg/m2 who do not achieve substantial or durable weight loss or co-morbidity improvement using nonsurgical methods.

Level of Evidence 2a

Grade of recommendation B

2. MBS for BMI 35–40 kg/m2 without obesity-associated medical problems

PRISMA Appendix 2 [PubMed, Cochrane, Embase] not enough studies

No Systematic Review Delphi Table 2

Although previous studies support the superiority of MBS compared to non-surgical therapy in patients with BMI ≥35 kg/m2 with no obesity-associated complications, there is a lack of high-grade evidence to support this item. Considering the lack of data from the literature, the leaderships of IFSO and ASMBS have convened a Delphi survey. According to the survey results of 49 experts, MBS is indicated in patients with class II obesity, a BMI of 35–40 kg/m2, with no associated medical problems in all groups of ages following a comprehensive multidisciplinary team (MDT) assessment. The consensus also supported the fact that MBS is cost-effective in patients with class II obesity when compared to non-surgical therapy.

Recommendation

  • MBS is recommended for patients with a BMI ≥35 kg/m2 regardless of the presence, absence, or severity of obesity-related complications.

Level of Evidence 5

Grade of recommendation D

3. BMI thresholds in the Asian population [36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54]

PRISMA Appendix 3

Systematic Review Table 3

Seven retrospective (54%, 2 multicenter) and 6 (46%) prospective studies reported the results of MBS on the Asian population. All articles have a good/fair quality. The articles investigated the effects of surgery on patients with BMI <30 kg/m2.

Eight articles reported results after RYGB, 5 after SG, 2 after OAGB, and one study after SADI-S with an overall medium follow-up of 33.4 [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84] months. Operative time and LOS appeared comparable to data already published in the literature for MBS in patients with a BMI >35 kg/m2.

All articles reported satisfactory weight loss with no mortality. Clavien–Dindo complications grades 3–4 ranged from 0 to 7.3%. Higher long-term nutritional complications were recorded after hypoabsorptive procedures. Remission from T2DM and HTN ranged from 38 to 100% and 30 to 83%, respectively.

Recommendations

  • Clinical obesity in the Asian population is recognized in patients with BMI ≥25 kg/m2. Access to MBS should not be denied solely based on the traditional BMI criteria.

Level of Evidence 2a

Grade of recommendation B

Extreme of Age

4. MBS in the older population [55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72]

PRISMA Appendix 4 [PubMed, Cochrane, Embase]

Systematic Review Table 4

Eighteen papers have been retrieved [55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72] for qualitative analysis. One RCT [56] and one prospective multicenter paper [62] have been found. Papers were categorized as comparative [55, 56, 62,63,64,65, 68, 69, 72] and non-comparative [57,58,59,60,61, 66, 67, 70, 71]. In the comparative group, two subgroups have been identified: older [age ≥ 65 years old] versus younger age [55, 65, 68, 69, 72]. SG, RYGB, and AGB were more representative surgical operations in these studies [56, 62,63,64]. The other studies were not comparative.

Five studies compared the intra- and post-operative complications of MBS between the elderly and non-elderly populations [55, 65, 68, 69, 72]. Despite the high-risk populations evaluated, the studies found no differences in postoperative complications, weight loss, and comorbidities resolutions.

Five studies evaluated the efficacy of AGB [57, 60, 61, 65, 71]. Despite its low peri-operative complication rates, all studies concluded that other procedures, such as SG or the RYGB, have better post-operative outcomes regarding weight loss and comorbidity resolution or improvement.

According to Gondal et al. [73], rather than age alone, frailty is independently associated with higher rates of postoperative complications following MBS. Furthermore, when considering MBS in older patients, the risk of surgery should be evaluated against the morbidity risk of obesity-related problems. Thus, there is no evidence to support an age limit on patients seeking MBS, but a careful selection that includes an assessment of frailty is recommended.

Two systematic reviews that included studies with elderly groups aged more than 60 years were found in the literature [74, 75]. Both supported MBS in the elderly with a careful selection of patients.

According to the literature, although there was only one RCT, we could state that MBS is a safe and effective treatment of the elderly in carefully selected cases. In this patient population, attention must be paid to patient selection and procedure selection, considering the chance of comorbidity resolution and post-operative follow-up compliance.

Recommendation

  • MBS has been performed successfully in increasingly older patients, including patients ≥70 years of age. In septuagenarians, compared with a younger population, MBS is associated with slightly higher rates of postoperative complications but still provides substantial benefits of weight loss and co-morbid disease remission.

  • Frailty, cognitive capacity, smoking status, and end-organ function have an important role in the indications for MBS.

  • There is no evidence to support an age limit for older patients seeking MBS, but a careful patient selection that includes a frailty assessment is recommended.

Level of Evidence 2a

Grade of recommendation B

5. MBS for the pediatrics and adolescents [76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117]

PRISMA Appendix 5 [PubMed, Cochrane, Embase]

Systematic Review Table 5

Forty-two papers have been retrieved for qualitative analysis [76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117]. One RCT [76] and 14 comparative papers [83, 88, 90, 93, 94, 96,97,98, 101, 104,105,106,107, 115] were found.

Seven studies about MBS versus lifestyle modifications [76, 88, 90, 94, 97, 105, 115] were evaluated. The surgical approach was more effective and durable than lifestyle modification regarding excess weight loss (%EWL), total weight loss (%TWL), and comorbidity resolutions.

Ten papers used the teen-LABS database [92,93,94,95,96,97,98,99,100,101], comparing different laparoscopic MBS procedures (AGB, RYGB, SG) to assess many aspects of MBS in pediatric and adolescent patients. All papers demonstrated an acceptable lasting %EWL with a good resolution of obesity-related complications.

Sixteen papers evaluated the efficacy of RYGB in adolescent patients [78, 85, 92, 95, 97,98,99, 101, 103, 105, 107, 108, 113, 115,116,117]; only six of them were comparative [97, 98, 101, 105, 107, 115]. All studies concluded that RYGB achieved good weight loss, improvement, and/or resolution of comorbidities in the pediatric and adolescent population with an acceptable complication rate.

A matched-control study evaluated the outcomes of MBS in Prader Willi syndrome (PWS) compared with a non-PWS group of patients and concluded that the SG is a well-tolerated, effective treatment option for PWS patients with obesity. In both groups, the weight loss and the resolution of the comorbidities were similar [96].

Alqathani et al., in a retrospective study with 10 years of follow-up, suggested that MBS would not negatively impact pubertal development or linear growth, and therefore, a specific Tanner stage and bone age should not be considered a requirement for surgery [96].

According to a literature review, the AGB seems to be a safer procedure. However, it achieved a lower weight loss, which was less durable than the RYGB or the SG.

Recommendation

  • MBS does not negatively impact pubertal development or linear growth.

  • MBS is safe in the population younger than 18 years and produces durable weight loss and improvement in comorbid conditions.

Level of Evidence 1b

Grade of recommendation A

Bridge to other Treatments

6. MBS prior to joint arthroplasty [120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141]

PRISMA Appendix 6 [PubMed, Cochrane, Embase]

Systematic Review Table 6 (some studies not in favor) Delphi Table 15

Twenty-two articles were chosen to be included in the present review.

Several studies have shown that patients with severe obesity (BMI ≥40 kg/m2) were at increased risk of major and minor complications after joint surgery. The American Association for Hip and Knee Surgeons (AAHKS) provided a consensus opinion recommending delaying elective surgery when the BMI exceeds 40 kg/m2, and in 2023, adherence to these recommendations was evaluated [142]. Pre-operative health optimization programs, including weight loss with MBS before joint surgery, have been implemented to reduce postoperative complications.

However, the current literature is unclear whether persons undergoing MBS have a lower risk of postoperative complications and need for revisions after joint surgery when compared to people with obesity who have not had MBS. This systematic review (Table 6) demonstrated that only one RCT was available. Additional results were obtained from cohort studies. Some studies have demonstrated the benefits of preoperative MBS, while others have highlighted the risks of prior MBS. In addition, it seems that MBS should be performed within 2 years before joint arthroplasty to decrease the negative impact of metabolic bone disease. Furthermore, given the setting of these studies, there is the possibility of bias due to the selection of patients.

In an RCT on 82 patients with obesity and osteoarthritis, 39 were randomized to AGB 12 months prior to total knee arthroplasty (TKA), and 41 patients were randomized to receive the usual nonoperative weight management prior to TKA. In a median follow-up of 2 years after TKA, 14.6% of patients in the MBS group incurred the primary outcome of composite complications, compared with 36.6% in the control group (difference 22.0%, P = .02). The incident TKA decreased by 29.3% in the MBS group because of symptom improvement following weight loss, compared with only 4.9% in the control group [133].

MBS can be performed safely before joint arthroplasty. However, further data are needed with specifically designed trials to clarify the causal role of MBS on the outcomes of subsequent joint arthroplasties.

Considering the conflicting data obtained from the literature, the IFSO and ASMBS decided to conduct a Delphi analysis on the topic of joint arthroplasty in patients with obesity (Table 15). This included the role of MBS as a bridge to joint arthroplasty and the proper time to arthroplasty after MBS.

During the two rounds of the Delphi analysis, the 49 experts reached a consensus on 5 statements concluding that MBS is indicated in patients with class II and III obesity (BMI of ≥35 kg/m2) even with no other medical conditions and in all age groups following a comprehensive multidisciplinary team assessment. In this survey, consensus was reached in four statements. First, MBS can be considered a bridge to joint arthroplasty in patients with a BMI ≥30 kg/m2. Second, MBS can decrease the operating time, risk of readmission, and short-term complications of subsequent joint arthroplasty in patients with a BMI ≥30 kg/m2. Third, MBS can decrease the need for joint arthroplasty in patients with BMI ≥30 kg/m2. Fourth, the experts also reached a consensus that joint arthroplasty in patients with a BMI ≥30 kg/m2 should be done 6 months to 1 year after MBS, depending on the severity of the joint disease, if there is weight loss stabilization and if the patient has good muscle mass and nutritional status.

Recommendation

  • Obesity is associated with poor outcomes after total joint arthroplasty. Orthopedic surgical societies discourage hip and knee replacement in patients with BMI ≥40 kg/m2, mainly due to the increased risk of readmission and surgical complications, such as wound infection and deep vein thrombosis.

  • Before total knee and hip arthroplasty, MBS has decreased operative time, hospital LOS, and early postoperative complications.

  • According to experts, MBS can be considered a bridge to joint arthroplasty in patients with BMI ≥ 30 kg/m2.

Level of Evidence 2b

Grade of recommendation B

7. MBS and abdominal wall hernia repair [143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165]

PRISMA Appendix [PubMed, Cochrane, Embase]

Systematic Review Table 7

Twenty-three studies were included [143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165]. Five studies were extracted from national registers, including the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) [144, 151], the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) [159], and the French hospital discharge summaries database system [154]. The other 18 studies were single-cohort retrospective studies. The studies were heterogeneous regarding timing and technique. Timing is mainly divided into ventral hernia repair (VHR) before MBS (symptomatic, low- or high-grade intestinal obstruction), concomitant VHR, and VHR after MBS. Some authors presented treatment algorithms regarding timing in their studies [147, 158, 161]. Of the 23 studies, 18 studies included a concomitant VHR and 5 studies a staged procedure [143, 147, 155, 162, 163]. Ventral hernias included epigastric, incisional, umbilical, paraumbilical, and Spigelian hernias, and one study reported the multistep approach in complex hernias with loss of domain [162]. Studies included primary and recurrent incisional hernia repair. VHR included open and laparoscopic techniques, with and without mesh. MBS included AGB, SG, and open and laparoscopic RYGB.

The studies analyzed postoperative morbidity and mortality, long-term complications, and recurrence rates. Abdominal wall hematoma, seroma, and surgical site infections were the most reported complications associated with all types of VHR. Small bowel obstructions (SBOs) and mesh dehiscence were reported in some studies, with the highest incidence of SBO at 37.5% in one study with deferred treatment [153].

Early mortality was reported in four register studies that analyzed concomitant VHR and was reported to be 0.3% [144], <1% [151], 0.2% [157], and 0.1% [159].

The literature presents a large amount of heterogeneous data regarding VHR in patients with obesity, and only five studies evaluated a staged approach. Due to the higher risk of reoperation for recurrence, VHR would be avoided in bariatric patients before MBS.

Recommendation

  • Obesity is a risk factor for the development of ventral hernias.

  • In persons with obesity and an abdominal wall hernia, MBS-induced weight loss is suggested before ventral hernia repair in order to reduce the rate of postoperative complications.

Level of Evidence 2b

Grade of recommendation B

8. MBS prior to organ transplantation [166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189]

PRISMA Appendix 8 [PubMed, Cochrane, Embase]

Systematic Review Table 8

Generally, extremely high or low BMI is considered a contraindication to solid organ transplantation (SOT) due to poor outcomes. Class III obesity may prevent access to transplantation since it is considered a relative contraindication and poses specific technical challenges during surgery [190, 191]. MBS, despite worldwide recognition as the most effective treatment for obesity, may be overlooked as an option in patients with severe end-stage organ disease. Nonetheless, MBS has been described in patients with end-stage organ disease to improve their candidacy for transplantation.

A systematic review of 2241 papers identified 24 thoroughly analyzed studies. The studies included different SOT summarized as heart/lung, kidney, and liver.

The literature search considered several variables, such as surgical procedures, disease status, patient age, and follow-up time. In many studies, specific data points such as weight loss, operative time, and complication rates were missing. In addition, there were differences between patients and studies, including different transplant timing and surgical techniques.

Recommendation

  • Obesity is associated with end-stage organ disease and may limit access to transplantation. Obesity is also a relative contraindication for solid organ transplantation and poses unique technical challenges during surgery.

  • Published data supports considering patients with end-stage renal disease and obesity grade 3 being able to be listed for kidney transplant after MBS.

  • MBS is shown to be safe and effective as a bridge to liver transplantation in selected patients who would otherwise be ineligible.

  • MBS can also improve heart transplants outcomes.

  • Limited data suggest that MBS could improve eligibility for lung transplantation.

  • MBS can be performed post-SOT or concomitantly to reduce complication rates and mortality.

Level of Evidence 2b

Grade of recommendation B

MBS in the High-Risk Patients

9.MBS for BMI ≥60 kg/m2 [192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238]

PRISMA Appendix 9 [PubMed, Cochrane, Embase]

Systematic Review Table 9

Forty-seven papers have been retrieved for qualitative analysis [192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238].

Twelve studies were focused on the safety and feasibility of MBS among patients with severe obesity at 30 days of follow-up after surgery with no reported data on weight loss or obesity-related comorbidities. Thirty-five studies analyzed MBS’s safety, feasibility, and medium to long-term results in patients with obesity and BMI ≥60 kg/m2.

Concerning weight loss, the mean initial BMI was ≥66.64 kg/m2 (SD ± 3.05). After a mean follow-up of 28 months, the mean %EBMIL was 51.5 (SD ± 16) with a mean ΔBMI of 21.64 kg/m2 (SD ± 7.16). Improvement or resolution of the obesity-related complications were reported in 17 studies, including patients with BMI ≥60 kg/m2. The mean percentage of improvement/resolution of T2DM was 67.35% (SD ± 24.79). The mean percentage of improvement/resolution of HTN was 54.01% (SD ± .93). The mean percentage of improvement/resolution of obstructive sleep apnea (OSA) was 63.61% (SD ± 21.51), while the mean percentage of improvement/resolution of dyslipidemia was 70.95% (SD ± 10.31).

Early complications (within 30 days from surgery) were reported in 45 studies.

The overall mean percentage of early complications was 7.57% (SD ± 6.28), and the mean percentage of early complications requiring reoperation was 4.9% (SD ± 3.48). The overall mean mortality was 1.61% (SD ± 2.29).

Long-term complications were reported in 13 studies. The mean percentage of long-term complications was 13.56% (SD ± 10.93).

Recommendation

  • MBS is safe and effective in patients with BMI ≥60 kg/m2.

  • Evidence suggests a higher rate of perioperative complications after MBS in patients with BMI ≥60 kg/m2.

  • According to the literature, MBS appears safe in patients with initial BMI ≥70 kg/m2.

Level of Evidence 2a

Grade of recommendation B

10 MBS in patients with liver cirrhosis [239,240,241,242,243,244,245,246,247,248,249,250,251,252,253]

PRISMA Appendix 10 [PubMed, Cochrane, Embase]

Systematic Review Table 10

Fifteen studies were included in this systematic review. Some studies differed between compensated and decompensated liver cirrhosis.

The early mortality was reported as 0.6 and 0.8% in the Metabolic Dysfunction-associated Liver Disease (MAFDL) or compensated liver cirrhosis, and 19.4 and 22.1% in decompensated liver cirrhosis. Mumatz et al. and Are et al. [245, 246] underlined the higher mortality of patients in low-volume centers (<50/year). Miller et al. analyzed 3032 patients undergoing SG (n = 1168) and RYGB (n = 1864) with compensated liver cirrhosis and reported early mortality in 21 (1.1%) of patients after RYGB and 10 patients after SG (<1%). Late mortality occurred in 42 patients after RYGB (2.2%) and under 10 patients after SG (<0.8%) [247].

Based on the current systematic review, patients with MAFLD or compensated liver cirrhosis have acceptable perioperative morbidity and mortality. However, patients with obesity and decompensated liver cirrhosis are at much higher risk for perioperative complications and perioperative mortality following MBS. Those patients should only be considered for surgery on a selective basis after a comprehensive risk assessment and only in high-volume centers. The risk of postoperative liver decompensation is low but should not be underestimated. Weight loss and remission of comorbidities are similar to the general bariatric surgical population. Careful patient selection and consideration of the choice of surgical procedure are important to ensure the best outcomes.

Recommendation

  • Obesity is a significant risk factor for MAFLD and liver cirrhosis.

  • MBS has been associated with histologic improvement of MAFLD and regression of liver fibrosis.

  • MBS is associated with a risk reduction of progression of MAFLD to liver cirrhosis.

  • MBS in patients with “decompensated” cirrhosis is associated with high perioperative mortality.

  • Careful patient selection and consideration of the choice of surgical procedure are important to ensure the best outcomes.

Level of Evidence 2b

Grade of recommendation B

11. MBS in patients with heart failure [254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271]

PRISMA Appendix 11 [PubMed, Cochrane, Embase]

Systematic Review Table 11

Thirty-one full-text articles were assessed for eligibility. Eighteen studies are included in the qualitative synthesis [254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271].

MBS is associated with a lower risk of major adverse cardiovascular events (MACE), including myocardial infarction, ischemic heart disease, or heart failure (HF) in patients with severe obesity [255,256,257].

The overall risk for early (less than 30 days) and late (30 days or more) complications was similar for patients with cardiovascular disease and the matched group that did not have cardiovascular disease [258,259,260,261,262]. Some studies reported an increased risk for early cardiovascular complications as well as a higher 90-day mortality rate (still within an acceptable range) for patients with heart disease, such as HF [263,264,265,266].

Current data suggest that MBS can be a useful adjunct to treatment in patients with obesity and HF before heart transplantation or placement of a left ventricular assistance device (LVAD) [266,267,268]. Patients who underwent MBS were observed to have improvement in cardiac function [269, 270]. This had several beneficial effects, such as a reduction in re-hospitalization for HF, and improvement in their left ventricular ejection fraction (LVEF). MBS could increase the patient’s likelihood of receiving a heart transplant. On the other hand, some patients had enough improvement in their cardiac function to no longer require a heart transplant [269, 270].

Recommendation

  • MBS in patients with obesity and HF is associated with improvement of LVEF, improvement of functional capacity, and higher chances for receiving heart transplantation.

  • In patients with obesity and HF, MBS has low morbidity and mortality and can be a useful adjunct before heart transplantation or placement of LVAD.

Level of Evidence 2b

Grade of recommendation B

Patient Evaluation

12. Multidisciplinary care [272,273,274,275,276,277,278,279,280,281,282,283,284]

PRISMA Appendix 12 [PubMed, Cochrane, Embase]

Systematic Review Table 12

The search screened 95 papers, but only 6 were thoroughly analyzed. There were guidelines or consensus statements, including those from the European Association for the Study of Obesity (EASO) and the European Association for Endoscopic Surgery (EAES) [272, 279]. Standardized pre-operative multidisciplinary evaluations have been reported to reduce major complications and reoperation rates.

The studies of this systematic review support the protective role of the multidisciplinary team (MDT) to ensure patient safety.

Registered experts in nutrition in MBS can assist in the management of post-operative patients who may experience issues such as food intolerances, malabsorption, micronutrient deficiencies, dumping syndrome, hypoglycemia, and RWG. Licensed mental health providers with specialty knowledge and experience in MBS behavioral health are necessary to assess patients for psychopathology and determine the candidate’s ability to cope with the adversity of surgery, the changing body image, and the lifestyle changes required after MBS.

Based on the EAES guidelines, scheduled multidisciplinary post-operative follow-up should be provided to every patient undergoing MBS [279].

Recommendation

  • MDT has an important role in MBS patients’ pre- and post-operative management.

Level of Evidence 2c

Grade of recommendation B

Revisional Surgery

13. Revisional MBS [285,286,287,288,289,290,291,292,293,294,295,296,297,298,299,300,301,302,303,304,305,306,307,308,309,310]

PRISMA Appendix 13 [PubMed, Cochrane, Embase]

Systematic Review Table 13

Twenty-six studies were selected for this systematic review. All studies were retrospective with a good/fair quality.

Recent articles report conversion from AGB and SG and revision of RYGB and OAGB. Revisional MBS is currently performed laparoscopically and robotically, with a growing trend toward a robotic approach. Operative time and LOS of revisional surgery were reduced with time and experience, which could be comparable to those reported in the literature for primary surgery.

All revisional and conversional interventions lead to additional weight loss. Clavien–Dindo complications 3–4 ranged from 0.9 to 26%. Mortality was lower than 1% for conversions from restrictive procedures, and up to 11.9% was reported after revisional stapling procedures. Revisional surgery appeared to induce further remission from T2DM and HTN.

Recommendation

  • Indication for revisional surgery after MBS varies among patients but may include insufficient weight loss, weight regain, insufficient remission of comorbidities, and management of complications (e.g., gastroesophageal reflux).

  • Due to its complexity, revisional MBS may be associated with higher rates of perioperative complications. However, revisional MBS induces satisfactory metabolic outcomes with acceptable complications and mortality rates.

Level of Evidence 2b

Grade of recommendation B

Discussion (see Criteria Table 16)

Table 16 Summary of recommendations with their grade and level of evidence
Full size table

The indications for MBS have not changed since the NIH proposed them in 1991. In other words, the indications have not kept up with the evolution of surgical technique from open laparotomy to minimally invasive, the changing procedure types, the improved safety of MBS, and the emerging evidence on numerous health benefits of weight loss.

IFSO and ASMBS joined forces to tackle this major problem, and the new MBS guidelines were published in October 2022. Updated guidelines based on current literature and data are vital as access to this life-saving surgery is still very low despite the available evidence—in most countries, access to MBS is less than 2% of eligible candidates.

This study systematically reviewed the best literature available for the outcomes of MBS for various populations with differing demographics and obesity-related complications. Eleven of the 13 criteria were supported by the literature. Where there was a lack of evidence, a Delphi process was employed to achieve expert consensus. PRISMA Prospect summarized the findings.

From these data, MBS impacted positively a range of populations and settings. The majority of examined populations had Grade B recommendations for the indications of surgery. Expert opinion (Grade D) was only relied upon to strengthen the evidence for the role of MBS in a few unique circumstances. This includes patients with a BMI of 35–40 kg/m2 who have no comorbidities, patients with a concurrent need for arthroplasty, and the role of the multidisciplinary team. Particularly in the pediatric and adolescent populations, the strength of the available data supported a Grade A recommendation. Improved access to surgery in adolescents was one of the two major new emphases of the new IFSO/ASMBS guidelines.

This systematic review highlights the need for well-designed RCTs or large prospective cohort studies to enable better-informed decision-making for clinicians and patients. Clinicians working in the field innately understand the benefit of multidisciplinary teamwork. However, it has yet to be proven in high-quality studies.

Just as the NIH indications from 1991 became outdated as surgical techniques, with a better understanding of the pathophysiology of obesity and improved perioperative safety, these current guidelines should be regularly revisited when new evidence emerges to inform treatment decisions.

List of Delphi consensus Experts

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