The duodenal switch (DS) is a variation of the biliopancreatic diversion and also works primarily by malabsorption.
The operation can be performed as an open operation through a midline incision from the base of the breastbone, or laparoscopically. Technically it is a complex operation which can take 5–7 hours to complete, and will usually require a post–op hospital stay of 4–6 days.
A large portion of the stomach is removed by dividing it lengthways along the inner curve (called a sleeve gastrectomy) and the pyloric valve at the bottom of the stomach (which regulates how quickly to stomach contents empty into the small intestine) is left intact. This means that although the food holding capacity of the stomach is reduced, its function remains intact.
A short segment of the duodenum at the base of the stomach is left but the remainder cut and the second half of the small intestine bought up and joined to the duodenum (this part of the operation is very similar to a RNY gastric bypass but is slightly lower down in the digestive tract).
Then, as in the BPD operation, the bypassed section of small intestine is then rejoined to carry bile and pancreatic juices to the latter part of the small intestine near where it joins the large intestine (colon).
Digestion and absorption of fat depends on it mixing with bile (from the liver and normally entering the duodenum). As this mixing does not occur until much further on in the intestine after a DS, the body's ability to digest and absorb calories from fat is severely reduced. As a result weight drops, even when eating quite normally.
Of all the operations, DS is associated with the greatest weight loss (after 2 years 80% of patients have achieved normal weight). However, the risks and side effects are also higher with a DS than with other operations.
The risk of death from surgery is the same as a RNY gastric bypass at 1 in 100 operations. However, about 30% of patients experience major problems with offensive wind and diarrhoea, resulting from the undigested fat and the upset to the normal balance of bacteria in the intestines. This can be minimised by following a low fat diet.
As well as preventing the absorption of fat and calories, the DS also hampers absorption of protein and essential minerals and vitamins such as iron, zinc and Vitamins A, D E and K. This can lead to a life threatening condition called protein–calorie malnutrition. Unfortunately, without regular follow up this condition can creep up and overwhelm the patient before anything can be done to correct it.
To avoid this happening, as well as taking vitamin and mineral supplements, DS patients need to take double the normal intake of protein in their diet for the rest of their life. For this reason a good multi–disciplinary team, and a patient committed to complying with diet, supplement instructions and to attending appointments are both vital ingredients to successful outcomes with this surgery.