The gastric bypass was introduced by Mason and Ito in 1966. It consists of separating the upper part of the stomach (fundus) from the remaining lower stomach (reducing stomach volume = restriction).The fundic pouch created in this manner (stomach pouch approx. 1/3 of total stomach volume) was then connected to a pulled up small bowel sling (jejunum). Because of extension of the pouch and the resulting larger meal sizes and the unfavourable effect on the weight-losing process, the gastric bypass was modified by successive reduction of the stomach pouch volume as well as stricture of the stomach-small bowel passage (delayed passage of chyme).
The procedure is laborious, changes the anatomy of the gastro-intestinal tract extensively, and is irreversible. In terms of patient comfort and weight control, good results were achieved. The percentage loss of weight may vary depending on author and sling length between 50 and 70%. Long-term complications may be deficiencies of iron, calcium, vitamin B and folic acid, as well as of liposoluble vitamins (A, D, E). While this method has experienced a renaissance in the German-speaking world since the end of the 90s, the gastric bypass is still the prevalent surgical bariatric procedure in the USA. This method has enjoyed particular popularity as it can be applied using laparoscopic techniques ("Keyhole techniques").
Compared to the intestinal bypass, complications are less common with this procedure. Lethality is between 0.8% (post-operative years) and 0.4% (Scopinario), provided the procedure is performed in an experienced medical centre and the after-care plan is strictly adhered to. The procedure includes extensive modifications to the normal anatomy of the gastro-intestinal tract and requires lifetime patient monitoring for deficiencies such as mineral (iron, calcium), vitamin (mainly liposolubles and vitamin B complex) and protein deficiencies, which immediately need to be countered by supplementation. Because of its efficiency in terms of weight loss, this method has gained popularity over the last view years, and except for Italy and some other European countries is also performed in the USA.
When applying gastric bypass procedures, in addition to restrictions (stomach volume reductions) a small bowel bypass is part of the Roux-Y-technique (see Fig. 3) for an additional malabsorptive effect. The limb originating from the duodenum contains the bile and pancreatic juices (digestive ferments) and is also called "biliopancreatic limb". The limb originating from the stomach contains chyme and is therefore also called the “alimentary limb”. By selecting different lengths for both limbs the malabsorptive effect may be changed.
The proximal gastric bypass, for example, produces a rather short re-routing distance for the digestive juices (Fig. 3), and in the long run there is an almost complete absence of severe deficiencies. Mostly iron supplements are required. Because of the lowest occurrence of long-term side effects and relatively high patient comfort the gastric bypass is considered the standard, and is the bypass procedure applied most often.
Bypass procedures with strong malabsorptive effects utilising diversion of digestive juices (bile and pancreatic secretions) over a long distance are called "biliopancreatic diversion" (Surgery according to Scopinaro (Fig. 2), distal (lower) gastric bypass, duodenal switch (Fig. 4)). The bile and pancreatic secretions entering the upper small bowel through the duodenum are diverted into the lower small bowel only 50 to 100cm above the colon opening. Thus the digestive path of fats, starches and proteins is shortened significantly. Paths of less than 50cm cause extreme deficiencies, and are therefore no longer applied. The laying of blind slings, as was performed in the jejuno-ileal bypass methods applied in the past (see also Bypass), is no longer performed because of occasionally even lethal complications caused by chronic liver failure. Severe deficiencies are very seldom thanks to optimisation of bypass limb lengths – even for biliopancreatic diversion or in distal gastric bypasses – and can be detected and treated easily from an early stage through periodical after-care. Permanent medication – apart from the prophylactic prescription of a vitamin-B-complex preparation during the first year and temporary supplementation of iron and calcium – is normally not necessary even after the low (distal) bypass or the biliopancreatic diversion.
By selecting different lengths of the small bowel limbs the proximal (high) gastric bypass of low malabsorption distinguishes itself from the distal (lower) gastric bypass of stronger malabsorption (biliopancreatic diversion, diversion of digestive juices).