Definitions
Obesity surgery refers to surgical interventions aimed at achieving sustainable weight reduction to improve comorbidities or their prevention and enhance quality of life. When the primary goal of surgical interventions is to improve glycemic metabolism in pre-existing type 2 diabetes mellitus, it is referred to as metabolic surgery.
The classification of obesity according to WHO is based on the Body Mass Index (BMI): body weight divided by height squared (kg/m²). For Europeans, obesity is classified into
- Grade I (BMI 30–34.9 kg/m²
- Grade II (BMI 35–39.9 kg/m²
- Grade III (BMI ≥40 kg/m²
Obesity is multifactorial; ultimately, a positive energy balance leads to the storage of excess energy primarily in adipose tissue and the liver. Weight reduction is associated with improvements in insulin resistance, blood sugar, blood pressure, blood lipids, gastroesophageal reflux, urinary incontinence, gonarthrosis, spinal complaints, intertrigo, infertility, obstructive sleep apnea syndrome, asthma, and a reduced risk of certain cancers.
Indications for Obesity and Metabolic Surgery
Sustainable weight reduction to improve comorbidities and quality of life in severe obesity is possible through dietary, exercise, behavioral, and pharmacotherapy alone or in combination, but is often not achieved [1 - 4]. Compared to conservative weight reduction measures alone or in combination, surgical therapy is significantly more effective and generally achieves the desired therapeutic goal [5 - 12].
The indication for an obesity surgery procedure is given under the following conditions [13 - 16]:
1. BMI ≥ 40 kg/m² without comorbidities and without contraindications after exhaustion of conservative therapy.
2. BMI ≥ 35 kg/m² with one or more obesity-associated comorbidities such as type 2 diabetes mellitus, coronary heart disease, heart failure, hyperlipidemia, arterial hypertension, nephropathy, obstructive sleep apnea syndrome, obesity hypoventilation syndrome, Pickwick syndrome, non-alcoholic fatty liver or non-alcoholic steatohepatitis, gastroesophageal reflux disease, asthma, chronic venous insufficiency, urinary incontinence, immobilizing joint disease, fertility restrictions, or polycystic ovary syndrome.
3. Primary indication for an obesity surgery procedure without prior conservative therapy attempt if one of the following conditions is present:
- BMI ≥ 50 kg/m²
- Conservative therapy attempt is deemed unpromising or hopeless by the multidisciplinary team.
- In patients with particularly severe comorbidities that do not allow delay of surgical intervention.
A primary indication in terms of metabolic surgery can be made with BMI ≥ 40 kg/m² and coexisting type 2 diabetes mellitus if the treatment goal is more focused on improving glycemic metabolism than weight reduction. For these patients, proof of exhausted conservative therapy in terms of obesity surgery is not required [17, American Diabetes Association 2017].
Contraindications for Obesity and Metabolic Surgery
In the following diseases and conditions, obesity and metabolic surgery is considered contraindicated despite currently lacking evidence:
1. Unstable psychopathological conditions, untreated bulimia nervosa, active substance dependence.
2. Consuming underlying diseases, malignant neoplasms, untreated endocrine causes, chronic diseases that worsen due to postoperative catabolic metabolism.
3. Existing or immediately planned pregnancy.
If the mentioned diseases and conditions can be successfully treated, re-evaluation should occur.
Not considered contraindications are:
- older age (≥ 65 years) [18]
- chronic inflammatory bowel diseases such as Crohn's disease and ulcerative colitis [19]
- existing desire for children [20]
- Type 1 diabetes [21]
Surgical Procedures
Effective surgical procedures for the treatment of obesity and its comorbidities include:
- Sleeve gastrectomy (SG)
- proximal Roux-en-Y gastric bypass (pRYGB)
- Omega-loop gastric bypass (MGB)
- biliopancreatic diversion with/without duodenal switch (BPD or BPD-DS)
There is no universally recommended surgical procedure for all patients; rather, the choice of procedure should be individually tailored to the patient's medical, psychosocial, and general life circumstances [22]. Current evidence does not allow the definition of an operative "gold standard" as a primary intervention in obesity and metabolic surgery.
In patients with extreme forms of obesity (BMI > 50 kg/m²) and/or significant comorbidity, staged concepts may be considered, e.g., initially sleeve gastrectomy, then gastric bypass, to reduce perioperative risk [23]. All procedures should ideally be performed laparoscopically.
1. Sleeve Gastrectomy (SG)
The SG was initially established in biliopancreatic diversion with duodenal switch (BPD-DS) for additional food restriction and ulcer prophylaxis. It has since become an independent surgical procedure. The SG was first described in 1993 by Marceau [24]. The SG is also very well suited as the first operation of a staged concept in extreme obesity, as the sleeve stomach can be easily converted into a Roux-en-Y gastric bypass, an Omega-loop gastric bypass, or a postpyloric bypass if needed [25].
The excess weight loss 2 years after SG does not differ significantly from the weight loss after pRYGB. After 5 years, the weight loss after SG is about 50%, and the remission rate of type 2 diabetes mellitus is 58% [26 – 30]. Compared to gastric bypass, the SG has significantly fewer perioperative complications. The morbidity after SG is reported to be 7 - 8% [15, 29, 31, 32, 33]. In large centers, the mortality is well below 1% [15]. The most common complications are staple line leaks, abscesses, or postoperative bleeding.
Currently, there are no clear contraindications for the SG. Only in the case of preoperatively proven symptomatic and/or therapy-resistant gastroesophageal reflux should the indication be critically assessed [29].
2. Proximal Roux-en-Y Gastric Bypass (pRYGB)
The pRYGB was previously referred to as the gold standard of obesity and metabolic surgery and was first described in 1967 and 1969 by Mason and Ito with relatively large pouch volume. Today, it is performed in the laparoscopic modification by Wittgrove from the 1990s with a very small pouch (< 15 cm³) [34, 35].
The pRYGB offers very good long-term results in terms of weight reduction and remission of pre-existing type 2 diabetes mellitus. In the meta-analysis by Chang et al., the average weight reduction after pRYGB compared to conservatively treated controls was 14 BMI points, Yu et al. determined 12.6 BMI points [36, 37]. After 5 years, an excess weight loss of 60 - 65% can be expected. The procedure leads to remission of pre-existing type 2 diabetes in an average of 75% [16, 37]. In the meta-analysis by Chang et al. [36], a mortality of less than 1% is reported for the pRYGB, morbidity is 21%, and the reoperation rate is 3%. The pRYGB thus has higher postoperative morbidity and reoperation rates compared to the SG, but the incidence of severe complications is comparable. Regarding effectiveness in T2DM, the pRYGB is superior to the SG.
3. Omega-Loop Gastric Bypass (MGB)
The Mini Gastric Bypass, or MGB, was first performed by Rutledge in 1997 and is considered a safe and effective procedure in obesity and metabolic surgery. The principle of the MGB is the formation of a long lesser curvature gastric pouch combined with a biliary intestinal loop, whose length can vary. Typically, it has a length from the Treitz ligament to the gastrojejunostomy of 200 cm. Depending on the severity of obesity, longer biliary limbs (250-300 cm) are chosen. In severe obesity, a length of 250 cm is recommended, in older patients and vegetarians a length of 180-200 cm, and in type 2 diabetics without massive obesity a length of 150 cm is recommended.
The conversion rate from laparoscopic to open procedure is between 0 and 1.23% [22]. The weight loss of the MGB is a reduction in BMI of 11.3 kg/m² or an excess weight loss between 61 and 69% after 12 months and 72.9 and 77% after 5 years [22, 38, 39]. For type 2 diabetes, remission rates between 51 and 100% are reported [39]. Weight loss and type 2 diabetes remission rate are greater after MGB than after a pRYGB [39].
The number of postoperative complications after MGB is between 0-28.6%. The most common are bleeding requiring endoscopic or surgical intervention (02, - 28.6%), and anastomotic ulcers (1 – 14.3%). The mortality rate is 0 - 0.5% [38].
4.1 Biliopancreatic Diversion (BPD)
The BPD was developed by Scopinaro in the 1970s [40, 41] and separates, similar to the pRYGB, the passage of food and digestive secretions bypassing the duodenum. Internationally, the BPD is considered a standard procedure, but it has hardly gained traction in Germany.
In the meta-analysis by Panunzi et al., this malabsorptive surgical procedure showed the highest remission rates for pre-existing type 2 diabetes mellitus among all bariatric surgical procedures [16]. Diabetes remission was achieved in 89% of patients after BPD, in 77% of patients after pRYGB, and in 60% of patients after SG. Similar results were also described by Müller-Stich et al. and Mingrone et al. [12, 42]. The same applies to excess weight reduction, although no high-quality data exist on this.
The perioperative mortality rate is reported in the meta-analysis by Panunzi et al. as 0.8% for the BPD. The BPD is predominantly based on the principle of malabsorption with strong fatty stools, which inevitably leads to reduced nutrient absorption such as fat-soluble vitamins. Various studies have observed a significant drop in vitamin A and E in up to 40% of patients. Vitamin D deficiency occurs in up to 61% of cases after BPD, iron and ferritin deficiencies in up to 16%, and zinc deficiency in 40 - 68% [43]. In a systematic review by Rodriguez-Carmona et al., it was shown that bone density can decrease significantly after BPD, posing a significant risk for the development of spontaneous fractures [44].
Malabsorptive surgical procedures also lead to impaired absorption and reduced efficacy of therapeutically relevant medications [45].
The overall complication rate after laparoscopic biliopancreatic diversion is up to 25% (gastric staple line insufficiencies, duodenal stump insufficiencies, incisional hernias, strictures of the duodenojejunostomy) [46]. In a retrospective observational study, a significantly higher percentage of necessary postoperative intensive care stays and orotracheal intubation treatments (30.5%) was found after BPD compared to gastric bypass and sleeve gastrectomy (12%). The mortality rate for the BPD was 6%, whereas no deaths were reported for SG and pRYGB [47].
4.2 Biliopancreatic Diversion with Duodenal Switch (BPD-DS)
The BPD-DS is a complex operation that combines restriction (sleeve gastrectomy) with malabsorption (postpyloric Roux-en-Y reconstruction).
It was first performed as an open operation in 1988 by Douglas Hess [48]. Due to the good results (sustainable weight reduction, high remission rate of pre-existing type 2 diabetes), the procedure became established and was first performed laparoscopically by Michael Gagner [49].
However, the BPD-DS is now a rarely performed procedure worldwide, accounting for at most 2% of all obesity and metabolic surgeries [50]. The reasons are likely the significantly increased perioperative morbidity and mortality compared to other procedures, as well as postoperative deficiencies that can occur in a high percentage despite substitution due to pronounced malabsorption [15, 51, 52, 53].