Sleeve gastrectomy is a simple and straightforward surgery to perform. The stomach is mobilized along the greater curvature and cut longitudinally with a linear stapler. The purpose of surgery is to modify the interaction between ingested food and stomach to alter certain neuro-hormonal signals. Signals as Ghrelin, GLP-1 and PYY affect metabolism, appetite, satiety and ultimately result in weight loss. Many bariatric surgeons have difficulty accepting the fact that metabolic surgery is more about altering these neuro-hormonal signals than mechanically restricting the stomach. Consequently, when gastric sleeve surgery was first introduced several years ago, the debate about bougie size dominated our metabolic and bariatric surgery field. Whole sessions in Obesity Week and other bariatric surgery conferences were devoted to discussing the optimal sleeve lumen diameter. The assumption, of course, was that the smaller the bougie diameter the better is weight loss. This assumption was proven wrong. Many published studies have shown that the smaller the bougie size the higher is the leak rate with no improvement in percent excess weight loss.

Knowledge about sleeve gastrectomy mechanism of action, predictors of weight loss and optimal surgical technique is still not established. As John Naisbitt said: “We Are Drowning in Information but Starved for Knowledge”. We will continue to be bombarded by studies that will not advance our practice or improve our skills. This newly published article: “Is a retained fundus seen on postoperative upper gastrointestinal series after laparoscopic sleeve gastrectomy predictive of inferior weight loss?” is a perfect example. It is a single center, retrospective study that includes 149 sleeve gastrectomy patients. Patients were divided into 4 groups depending on the ratio of fundus to more distal sleeve lumen diameter, measured on postoperative upper gastrointestinal series (UGI). The authors found no difference in mean percent excess weight loss at one year following sleeve gastrectomy in all 4 groups. Of note, a single surgeon performed all 149 sleeve gastrectomies using a 34 French bougie. A 1 cm distance from GEJ was left at the angle of His.

I should mention that a postoperative UGI is not an accurate measure of sleeve lumen. The resected stomach is edematous, blood clots may be present along the staple line and sleeve lumen contrast filling is not homogeneous. Accepting this limitation, the study doesn’t show a difference in weight loss even when comparing the most optimally resected gastric fundus to the severely retained fundus. So how much gastric fundus should be resected to achieve the best weight loss? The answer to this question depends on the sleeve mechanism of action. If pure restriction is the dominant mechanism of action then the smaller the sleeve volume the better is weight loss. This however is not the case. Indeed, I preserve most of the antrum to prevent narrowing at the incisura angularis and to maintain the gastric pump that promotes gastric emptying. Most importantly, I preserve the antrum to maintain the Magenstrasse gastric emptying pathway. I believe that sleeve gastrectomy mechanism of action relies on restoring the Magenstrasse pathway of gastric emptying. This allows for rapid delivery of ingested food particles into the distal intestines stimulating the neuro-hormonal signals that result in weight loss. The Magenstrasse emptying pathway depends on antral wave contractions. Accordingly, mutilating the gastric antrum along a 34 French bougie is not necessarily associated with the best weight loss results. Discussing optimal gastric fundus resection in the setting of a resected antrum is not likely to yield any meaningful results. Preserving the antrum and optimally resecting the gastric fundus seem to be the best approach for sleeve gastrectomy. But what is optimal gastric fundus resection? The fundus can be completely resected flush at the GEJ. Part of the fundus may also be left unresected leaving a gastric bubble. At Houston Weight Loss Surgery center, we have found that aggressive gastric fundus resection is not associated with better long-term weight loss results. Rather, aggressive gastric fundus resection results in severe restriction and very limited gastric capacity. Patients typically reports uncomfortable restriction during the first 6 months of surgery without the benefit of increased weight loss. I have learned from observing such patients that mechanical restriction is not the dominant mechanism for weight loss. Excessive restriction following sleeve gastrectomy is not associated with better weight loss. I leave one cm of gastric tissue at the GEJ to prevent narrowing in that area and avoid patient discomfort. I resect most of the posterior gastric fundus by applying proper retraction during surgery. does leaving a larger unresected fundus lead to poor weight loss? The answer to this question maybe a yes but the cause is not poor restriction. Leaving a larger fundus may result in slower gastric emptying and poor Magenstrasse wave formation. Studies are needed to prove or disprove these observations. One thing for sure, we have had plenty of studies demonstrating that mechanical restriction by itself is not the underlying cause for weight loss. Yet, many still believe, like the authors of this article that “restriction is considered to be one of the most important mechanisms for weight loss in stapled procedures”.