Laparoscopic sleeve gastrectomy is a bariatric surgery procedure. As its name implies, it is performed laparoscopically - rather than opening a large incision, the surgeon instead makes small slits through which a laparoscope can be passed. 'Sleeve gastrectomy' decribes the type of operation. Gastrectomy means, roughly, 'gastric removal' - in this case it is the removal of a portion of the patient's stomach. It is called a sleeve because the point of the operation is to convert the stomach from an oblate pouch to more of a cylinder. This has the primary effect of lowering the capacity of the stomach, which is the means by which the surgery helps the patient lose weight.
Other forms of bariatric surgery are either malabsorptive — meaning that they change the way the body absorbs nutrients, either as a primary or secondary effect — or they introduce foreign objects into the body cavity. Gastric bypass and duodenal switch, two other types of gastric surgery, both change the shape of the alimentary canal. In the case of the bypass, it removes the pyloric valve, making it more difficult for the body to retain any food in the resultant tiny stomach pouch. This method thus changes how long food is held at each point, and changes the rate of absorption of nutrients and may change the types of nutrients that can be absorbed normally. For example, nutrients or other substances absorbed through the stomach lining will be lessened due to the limited stomach area and much lowered retention time. The duodenal switch involves bypassing part of the digestive tract below the stomach to deliberately limit the amount of nutrients that can be extracted. While leading to more effective weight loss, it can also lead to issues with nutrition as certain vitamins and other necessities are best absorbed by the portion of the gut which is resected.
The third option is the Lap-Band. This method involves placing a restrictive band around the stomach to limit its capacity. Although it has the benefit of not requiring any surgical compromise of the organs, it also means placing a permanent foreign body into the body cavity - and in addition, since it works by pressure rather than physical attachment, it can slip out of place or allow bulging of the stomach to occur, both of which require surgical intervention to correct.
The gastric sleeve, while not as effective as the two malabsorptive methods and involving more surgical compromise the Lap-Band, is nevertheless a happy medium. The stomach is stapled along its length to create a cylinder of useful space as opposed to a sac, and the excess stomach is then removed. This has the advantage of retaining the pyloric valve as well as much more absorptive area in the stomach, and not touching the rest of the alimentary canal.
Leakage from the stomach in the several weeks post surgery is the primary risk, as it can lead to peritonitis. This risk is shared with the switch procedures, and is actually much less in this case as the stomach is a much sturdier organ than the duodenum, small intestine, colon, etc. As a result, leakage is much less likely, and since it is higher in the process, does not generally involve nearly as much intestinal flora if it does occur.
Loss of between 55% and 75% of the 'excess body weight' — that is, above the notional normal for a patient's height — is typical, sometimes much more if the patient is able and willing to make or sustain lifestyle changes in addition to the surgery.