TABLE 1
How size is classified using the body mass index
| BMI | Classification | Risk of illness and comorbidity |
|---|---|---|
| <18.5 | Underweight | Increased |
| 18.5–24.9 | Normal | Average |
| 25–29.9 | Overweight | Increased |
| 30–34.9 | Obese (class I) | Moderate |
| 35–39.9 | Obese (class II) | Severe |
| ≥40 | Morbid obesity (class III) | Very severe |
| ≥50 | “Severe morbid obesity” | !!! Severe |
Most agree that bariatric surgery originated nearly 60 years ago with the jejunoileal bypass, a purely malabsorptive procedure in which the proximal jejunum was anastomosed to the distal ileum.7-9 This operation was based on the observation of dramatic weight loss following major small-bowel resection. The procedure was thought to allow obese patients to eat with abandon, thanks to the limited absorptive ability of the small intestine’s mucosal surface, which would impede digestion. However, the operation was fraught with complications, including protein calorie malnutrition, bacterial overgrowth, and even death. In addition, despite the dramatic reduction in the absorptive surface of the small intestine, some patients eventually regained weight.
One may still encounter patients who underwent jejunoileal bypass many years ago. One particular complication of this procedure is worth mentioning: hepatic cirrhosis. Any patient who has a history of jejunoileal bypass should have her liver function assessed before undergoing procedures that require general anesthesia.
At present, bariatric surgery may incorporate a component of malabsorption, but no other procedures are purely malabsorptive ( TABLE 2 ).
TABLE 2
Bariatric procedures for weight reduction, past and present
| Mechanism of action | Procedure |
|---|---|
| Malabsorptive | Jejunoileal bypass* |
| Restrictive | Vertical banded gastroplasty Gastric banding (Lap-Band) Laparoscopic sleeve gastrectomy Magenstrasse and Mill operation |
| Combination (malabsorptive and restrictive) | Roux-en-Y gastric bypass Biliopancreatic diversion Duodenal switch |
| Other | Gastric pacing† |
| * No longer performed | |
| †Experimental | |
Restrictive procedures
Vertical banded gastroplasty (VBG). This procedure is one of the earliest successful restrictive procedures ( FIGURE 2 ). Although it was originally performed via laparotomy, it is easily carried out laparoscopically. However, a risk of complication, such as severe reflux, and a low long-term success rate have decreased its widespread application.
Laparoscopic adjustable silicone band. The most common restrictive procedure performed today is the laparoscopic adjustable silicone band (Lap-Band) ( FIGURE 2 ). Among its benefits are:
- easy insertion, especially in comparison with the gastric bypass
- ability to adjust the amount of restriction (not possible with VBG)
- elimination of the need for supplemental nutrition
- reversibility.
Long-term results from a US population are not available because FDA approval did not occur until 2001. However, some centers outside the United States have reported unfavorable long-term outcomes. (See “Lap-Band complications may be pervasive,”.)
Laparoscopic sleeve gastrectomy (LSG). This operation was originally devised as the first stage of a duodenal switch. However, weight loss with this stage alone made LSG a bariatric procedure in its own right ( FIGURE 2 ).
Although this operation is categorized as restrictive, gastric sleeve resection eliminates the gastric fundus, the major site where ghrelin—“the hunger hormone”—is produced. This hormonal alteration may contribute to weight loss that occurs after LSG.
Magenstrasse and Mill operation. This operation converts the stomach into a long tube similar to the gastric sleeve. The greater curvature of the stomach is separated from the newly created tube but remains attached to the rest of the stomach at the antrum. (The greater curvature of the stomach is resected in the gastric sleeve procedure.)
Many insurers refuse to reimburse for restrictive operations other than the VBG and Lap-Band.
FIGURE 2 Three common surgeries
These restrictive procedures decrease the size of the stomach reservoir without impairing absorption of calories.
Combination procedures
Biliopancreatic diversion, duodenal switch. Despite the risk of protein malnutrition, these two procedures attempt to produce selective malabsorption of fat and carbohydrate as a means of treating the most severely obese patients. These operations carry the highest mortality rate and are therefore less likely to be offered routinely.
Roux-en-Y gastric bypass (RYGB). In the United States, the RYGB is performed more frequently than other procedures that combine malabsorption and restriction. It is considered by most to be the “gold standard” bariatric operation ( FIGURE 3 ).
The RYGB may induce weight loss through one or more of the following mechanisms:
- a decrease in the size of the gastric pouch. After the procedure, this pouch has a capacity of about 30 cc (size of a thumb)
- the small diameter of the gastrojejunal anastomosis, which is usually 1 cm
- glucose intolerance. About 50% of patients experience dumping symptoms when they ingest refined carbohydrates
- subclinical malabsorption. Food does not encounter the majority of digestive enzymes until it reaches the jejunojejunostomy anastomosis
- suppression of ghrelin production. Ghrelin is a hormone produced primarily in the gastric fundus and secondarily in the duodenum, both of which are bypassed with the RYGB. Plasma ghrelin levels peak before meals and are suppressed with food intake. After RYGB, patients demonstrate a flattening of this pattern, which appears to correlate with a suppression of appetite.10
