Anatomy - Anastomosis technique, gastrointestinal, with circular stapler

Large and small intestine have a very similar wall structure. The reduced mechanical strength of strictly mucosal sutures stems from the small amount of connective tissue and collagen fibers in the mucosal layer.
Comprising connective tissue with a three-dimensional collagen fiber lattice and elastic meshes, the submucosa constitutes the “load-bearing” part of the intestinal sutures in all parts of the digestive tract. The muscularis layer is also a reliable suture line, and the serosal covering allows for a gas- and fluid-proof seal as a result of fibrin exudation within just 4-6 hours after intestinal suturing.

The large intestine plays a special role here. Its complication rate is higher because of various characteristics. This is due to low collateral circulation, the lack of serosal covering on parts of the ascending and descending colon and on the entire extraperitoneal rectum, and a lower mural collagen concentration in the large intestine with higher collagenase activity. In addition, since the concentration of bacteria increases by a factor of 10 million, there is a greater risk of infection. And anaerobes are 1,000 times more common in the large intestine than aerobic bacteria.

Leak-proof anastomosis by secure suturing is an indispensable part of abdominal surgery. All gastrointestinal sutures have two objectives: First, to restore a liquid- and gas-proof inner layer with the least ischemic effect possible on the transection margins. And secondly, to ensure resistance to all physical stresses and strains such as fluctuating intraluminal pressure, peristalsis, longitudinal tension and external pressure from adjacent organs. All of this should take place using a simple and rapid technique with the goal of minimizing contamination of the surgical field and implanting as little of the best tolerated foreign body material as possible.

Suture material causes foreign body reactions in the tissue; it supports and impairs healing at the same time. Animal studies on burst pressure confirm that the strength of an anastomosis decreases until the fourth day and then increases once again until normal levels are reached at around day 10.

Nevertheless, the suture material still acts as a foreign body that delays healing and increases the risk of pathogen infection. There are various options for decreasing this foreign body irritation Minimizing the mass of suture material to be implanted, use of absorbable substances persisting only for the duration of the actual load bearing function, and use of materials with only a low potential for irritation.

As with other wounds, intestinal anastomoses heal in three phases, . Lasting until day 4, the first phase is characterized by exudation of fibrin and blood components. During this time, the mechanical strength of the suture depends on the suture material used. In the second phase from day 4 to 14, vessel and fibroblast proliferation dominate. During the next phase of several months, the layers of the intestinal wall will reorganize.

In surgery of the esophagus, stomach and rectum, the use of machine suturing devices has proven its effectiveness Here, the principle of layer-specific adaptation is deliberately avoided. The key to success lies in the primarily secure air-tight and fluid-tight suture line.

Since Ravitch and Steichen improved the technique and instruments (1979) with the introduction of the EEA stapler, stapled gastrointestinal anastomoses have become more and more common.
Stapled anastomoses implement a double-layered full-bite suture and benefit from an atraumatic, uniformly adapted seam suture line. The stainless-steel staples cause only mild tissue reactions. The staples become encapsulated, and their risk of migrating during MRI studies can almost be ruled out and is irrelevant.
All EEA cartridges have the same staple dimensions. They only differ in the number of staples which depends on the selected cartridge diameter. Within the cartridge the staples are staggered in two circles. Firing reshapes the staples to a “B” and always fashions a double-layered suture line penetrating all layers. After firing, the staples may be reshaped into a fully closed B-shape, or may vary in height and shape within a given tolerance range to account for uneven tissue thickness.
The B-shape does not compress the intramural blood vessels and preserves the capillary blood supply to the suture line.
Anastomoses created with circular staplers are inverting. After the staples have been reshaped a circular blade within the staple housing resects any intraluminal tissue protruding from the suture line. The anastomosis can be fashioned with various staplers and cutters because they are available in various sizes.

The benefits of mechanical versus handsewn anastomosis are mainly due to the following criteria: Greatly speeded up anastomosis process, tension-free and better uniform suture, maintenance of tissue perfusion as a result of the B shape of the closed staples, less tendency for swelling, small non-septic working volume, greater potential for standardization, high reproducible suture security, and broadened surgical indication.

This is offset by:

• In  emergent procedures, staplers and cutters are of only limited use, as in such cases the intestinal wall is usually thickened by edema and exceeds the tolerance limit of tissue approximation. Mechanical sutures are also not recommended in chronic inflammatory bowel disease (Crohn disease, ulcerative colitis).
• The use of staplers and cutters requires special knowledge of the technique and a personal training program prior to clinical application.
• Staplers cannot be “customized” to every surgical situation. In challenging technical situations, handsewn sutures are preferred.

Therefore: As temptingly easy staplers might seem, the surgeon must have mastered both handsewn and mechanical suturing techniques. Since hand suturing will always be the last resort in critical situations, it is therefore a basic technique in surgical residency training!