Definitions
Bariatric surgery refers to operative procedures intended to achieve, through sustained weight reduction, an improvement in comorbidities or their prophylaxis and an improvement in quality of life. When the primary aim of the operative procedures is to improve the glycaemic metabolic state in pre-existing type 2 diabetes mellitus, this is referred to as metabolic surgery.
The WHO classification of obesity 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 in origin; ultimately, a positive energy balance leads to storage of excessively supplied energy mainly in the adipose tissue and the liver. Weight reduction is associated, among other things, with an improvement in insulin resistance, blood glucose, blood pressure, blood lipids, gastro-oesophageal reflux, urinary incontinence, gonarthrosis, spinal complaints, intertrigo, infertility, obstructive sleep apnoea syndrome, asthma, and a reduction in the risk of certain cancers.
Indications for bariatric or metabolic surgery
Sustained weight reduction to improve comorbidities and quality of life is possible in higher-grade obesity through nutritional, exercise, behavioural, and pharmacotherapy, alone or in combination, but is frequently not achieved [1 - 4]. Compared with conservative measures for weight reduction alone or in combination, surgical therapy is considerably more effective and, as a rule, achieves the intended treatment goal [5 - 12].
The indication for a bariatric surgical procedure is given under the following conditions [13 - 16]:
1. BMI ≥ 40 kg/m² without accompanying diseases 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, hyperlipidaemia, arterial hypertension, nephropathy, obstructive sleep apnoea syndrome, obesity hypoventilation syndrome, Pickwick syndrome, non-alcoholic fatty liver or non-alcoholic steatohepatitis, gastro-oesophageal reflux disease, asthma, chronic venous insufficiency, urinary incontinence, immobilising joint disease, fertility restrictions or polycystic ovary syndrome.
3. Primary indication for a bariatric surgical procedure without prior conservative therapy attempt if one of the following conditions is present:
- BMI ≥ 50 kg/m²
- Conservative therapy attempt is assessed by the multidisciplinary team as not promising or futile.
- In patients with particular severity of concomitant and secondary diseases that do not allow postponement of a surgical procedure.
A primary indication in the sense of metabolic surgery can be made for BMI ≥ 40 kg/m² and coexisting type 2 diabetes mellitus if the treatment goal is to improve the glycaemic metabolic situation more than weight reduction. To establish the indication for surgery, proof of exhausted conservative therapy in the sense of bariatric surgery is not required for these patients [17, American Diabetes Association 2017].
Contraindications for bariatric or metabolic surgery
For the following diseases and conditions, bariatric or metabolic surgery is considered contraindicated—despite currently lacking evidence:
1. Unstable psychopathological conditions, untreated bulimia nervosa, active substance dependence.
2. Wasting/consumptive underlying diseases, malignant neoplasms, untreated endocrine causes, chronic diseases that worsen due to a postoperative catabolic metabolism.
3. Existing or imminently planned pregnancy.
If the aforementioned diseases and conditions can be successfully treated, a re-evaluation should be carried out.
The following do not constitute contraindications:
- advanced age (≥ 65 years) [18]
- chronic inflammatory bowel diseases such as Crohn's disease and ulcerative colitis [19]
- existing desire to have children [20]
- type 1 diabetes [21]
Surgical procedures
The effective surgical procedures for treating 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 surgical procedure that can be recommended across the board for all patients; rather, the choice of procedure should be based individually on the patient's medical, psychosocial and general life circumstances [22]. The current evidence does not permit the definition of a surgical "gold standard" as a primary procedure in bariatric and metabolic surgery.
In patients with extreme forms of obesity (BMI > 50 kg/m²) and/or significant comorbidity, staged concepts can 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 established as 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, if required, be readily converted into a Roux-en-Y gastric bypass, an omega-loop gastric bypass or a post-pyloric bypass [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 around 50%, and the remission rate of type 2 diabetes mellitus is 58% [26 – 30]. Compared to gastric bypass, the SG shows in part significantly fewer perioperative complications. The morbidity after SG is reported as 7 - 8% [15, 29, 31, 32, 33]. In large centres, the mortality is well below 1% [15]. The most common complications are fistulas of the staple line, abscesses or postoperative bleeding.
There are currently no clear contraindications for the SG. Only in the case of preoperatively demonstrated symptomatic and/or therapy-refractory gastro-oesophageal reflux should the indication be viewed critically [29].
2. Proximal Roux-en-Y gastric bypass (pRYGB)
The pRYGB was in the past referred to as the gold standard of bariatric and metabolic surgery and was first described in 1967 and 1969 by Mason and Ito, initially with a relatively large pouch volume. Nowadays, 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 regarding 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 on average to remission of pre-existing type 2 diabetes in 75% [16, 37]. In the meta-analysis by Chang et al. [36], a mortality of under 1% is reported for the pRYGB, the morbidity is 21%, and the reoperation rate is 3%. Thus, the pRYGB has a higher postoperative morbidity and reoperation rate compared to the SG, 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, abbreviated MGB, was first performed in 1997 by Rutledge and is considered a safe and effective procedure in bariatric or metabolic surgery. The principle of the MGB is the formation of a long lesser curvature gastric pouch combined with a biliary small intestine loop, whose length can vary. Usually, it has a length from the ligament of Treitz to the gastrojejunostomy of 200 cm. Depending on the severity of obesity, longer biliary limbs (250-300 cm) are also chosen. For severe obesity, a length of 250 cm is recommended, for older patients and vegetarians a length of 180-200 cm, and for type 2 diabetics without massive obesity a length of 150 cm.
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 (0.2 - 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 in the 1970s by Scopinaro [40, 41] and, similar to the pRYGB, separates the passage of food and digestive secretions while bypassing the duodenum. Internationally, the BPD is regarded as a standard procedure, however it has hardly become established in terms of numbers in Germany.
In the meta-analysis by Panunzi et al., it was shown that this malabsorptive surgical procedure has the highest remission rates for pre-existing type 2 diabetes mellitus among all bariatric surgical procedures [16]. Diabetes remission could be 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 there are no high-quality data on this.
The perioperative mortality rate is reported as 0.8% for the BPD in the meta-analysis by Panunzi et al. The BPD is based predominantly on the mechanism of malabsorption with severe steatorrhoea, which inevitably leads to reduced nutrient absorption, such as of fat-soluble vitamins. In various studies, a significant decrease in vitamin A and E was observed in up to 40% of patients. Vitamin D deficiency states occur 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 could be demonstrated that bone density can decrease considerably after BPD, which carries a considerable risk for the development of spontaneous fractures [44].
Malabsorptive surgical procedures also lead to a restricted absorption and to a reduced effect of therapeutically relevant medications [45].
The overall complication rate after laparoscopic biliopancreatic diversion is up to 25% (leaks of the gastric staple line, duodenal stump insufficiencies, incisional hernias, strictures of the duodenojejunostomy) [46]. In a retrospective observational study, a considerably higher percentage of necessary postoperative intensive care stays and orotracheal intubation treatments (30.5%) was found after BPD than after gastric bypass and sleeve gastrectomy (12%). The mortality rate for the BPD was 6%, whereas no death was reported for SG and pRYGB [47].
4.2 Biliopancreatic Diversion with Duodenal Switch (BPD-DS)
The BPD-DS is a complex operation that combines a restriction (sleeve gastrectomy) with a 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 could establish itself and was first performed laparoscopically by Michael Gagner [49].
In the meantime, however, the BPD-DS is a procedure that is rather rarely performed worldwide and accounts for at most 2% of all bariatric or metabolic procedures [50]. The cause is likely to be the considerably increased perioperative morbidity and mortality compared to other procedures, as well as postoperative deficiency states which, despite substitution, can occur in a high percentage owing to the pronounced malabsorption [15, 51, 52, 53].