The more obese a person is, the more risks they face at operation. In some cases, surgery has been denied to those with a BMI of over 60kg/m² (super obese) because of these risks.
If you have read the pages about RNY gastric bypass and duodenal switch, you will see that they are complex operations, sometimes taking a number of hours to do. If a patient is super obese or has severe obesity–related conditions, their health state makes that complexity of operation too risky to proceed with.
So increasingly, surgeons are recommending that for this group of patients, surgery should be considered in two stages; initially a sleeve gastrectomy followed at a later date by a second operation to convert it to either a RNY gastric bypass or to a duodenal switch. However, some patients will lose enough weight with a sleeve gastrectomy alone, so that the second stage of the operation is not required.
The sleeve gastrectomy reduces the size of the stomach by about 75%. It is divided vertically from top to bottom leaving a banana shaped stomach along the inside curve and the pyloric valve at the bottom of the stomach, which regulates the emptying of the stomach into the small intestine, remains intact. This means that although smaller, the stomach function remains unaltered.
Because the patient can only eat a small meal, they will lose weight, especially if they also comply with a low fat, low sugar diet. Because of the reduced stomach size, the patient will also keep the feeling of fullness for longer, helping them to eat just three meals per day. However, they suffer none of the side effects experienced by bypass patients because the digestion is unaltered.
This operation is relatively quick to perform, can usually be done laparoscopically and the hospital stay post–operatively is normally 1–2 days.
Most patients lose 30–50% of their excess weight in the first 12 months after a sleeve gastrectomy operation. The timing of the second stage operation ranges from 12–18 months after the first, depending on the degree of weight loss.