Abstract
Anastomotic techniques have greatly improved over the past two centuries, and postoperative complications have fallen accordingly. Factors contributing to anastomotic failure include location and systemic diseases such as sepsis and hemorrhagic shock. Factors that have not demonstrated any difference in outcome include stapled versus hand sewn anastomosis, continuous versus interrupted sutures, and single versus two layer anastomosis. Successful intestinal anastomosis necessitate adequate exposure and access, gentle tissue handling, absence of tension and distal obstruction, hemodynamic stability with adequte tissue oxygenation, and meticulous surgical technique.
INTRODUCTION
An intestinal anastomosis becomes necessary when a segment on the gastrointestinal tract is resected for benign or malignant indications and gastrointestinal continuity needs to be restored. The art of bowel anastomosis dates back into the 19th century. Nicholas Senn's review (1844–1908, Chicago) performed in 1893 detected approximately 60 different techniques for intestinal suture, which he attributed to the “ancient and modern methods,” followed by an additional 33 “recent methods” of suturing bowel (1). Within the past 200 years, gastrointestinal anastomosis has been transformed from a life-threatening venture into a safe and routinely performed procedure. Among these advances was the transition to scientifically-based medicine, chiefly the knowledge of the importance of serosa apposition introduced by Antoine Lembert (1802–1851) in 1826 (2) and the concept of asepsis proposed by Lord Joseph Lister (1827–1912) in 1867 (3). Additional modern advancement in bowel anastomosis included the advent of stapling device. Although the Murphy Button described in 1892 was the first popular stapling prototype (3), further progress was not remarkable until the early 1960's when the Institute for Experimental Apparatus and Instruments in Moscow developed a group of instruments capable of performing gastrointestinal tract anastomosis (4). However, these instruments were cumbersome and required individual staples be inserted by hand prior to each use. Several further engineering feats, including Ravitch's introduction of a modified form of the Russian stapling device and advent of biofragmentable anastomosis rings in 1985 led to the resurgence of sutureless anastomosis around the world (4–5). Even today, intestinal anastomosis can be performed in a variety of ways; the specific technique is usually a function of surgeon preference.
FACTORS IN ANASTOMOTIC HEALING
In 1882, Halsted was already drawing attention to the idea that the collagen content in the submucosal layer was the main factor responsible for the resistance of anastomosis (6). The process of intestinal anastomotic healing is similar to wound healing elsewhere in the body and can be divided into (A) acute inflammatory (lag) phase, (B) proliferative phase, and (C) remodeling or maturation phase. A critical stage in collagen formation is the hydroxylation of proline during maturation phase to hydroxyproline, which gives the molecule its structural strength. The bursting pressure of an anastomosis is often used to gauge the strength of the healing process. This pressure has been found to increase rapidly in the early postoperative period, reaching 60% of the strength of the surrounding bowel by three to four days and 100% by one week (7). For the purpose of a bowel anastomosis, it is important to keep in mind that the serosa (i.e. the visceral peritoneum) holds suture better than the musclar layers of bowel. The absence of a peritoneal layer makes anastomosis of the thoracic esophagus and the rectum below the peritoneal reflection technically more difficult than anastomosis of the intraperitoneal segments of the intestine. In addition, the stomach and the small bowel are more vascularized than the esophagus and the large bowel and consequently tend to heal more rapidly.
FACTORS IN ANASTOMOTIC FAILURE
Failure of an anastomosis with leakage of intestinal contents is one of the most significant surgical complications. Reported failure rates range from 1 to 24%, depending on what type of anastomosis was performed and whether the operation was an elective or an emergency procedure (8). An anastomotic leak increases the morbidity and mortality associated with the operation: it can double the length of the hospital stay and increase the mortality by threefold (9). Signs and symptoms suggestive of an anastomotic leak include postoperative (usually between days four to seven) abdominal pain or peritonitis, fever, leukocytosis, and tachycardia, all of which can point to developement of systemic inflammatory response syndrome (SIRS) or sepsis. In the elderly, chest pain and new-onset arrhythmias may be the first sign of leak. An abdominal X-ray showing free air or a CT scan with pneumoperitoneum and significant free fluid or inflammatory changes around the anastomosis are suggestive of an anastomotic failure. A localized anastomotic leak that is not associated with peritonitis or significant systemic sepsis can be managed with percutaneous or open drainage of the abscess, however anastomotic leaks associated with peritonitis or systemic manifestation of sepsis require a laparotomy and either revision of the anastomosis if feasible or fecal diversion proximally or at the site of the anastomosis.
Factors contributing to anastomotic failure include location and systemic factors. As a rule, for any given technique the location of the anastomosis does not significantly influence the overall leakage rate. There are two exceptions to this general rule. First, low anterior rectal anastomosis are associated with higher leakage rates ranging from 12–19% (10). Second, esophageal anastomosis are associated with leakage rates of about 3% when stapled technique is used (11). Systemic factors including sepsis, anemia, diabetes mellitus, previous irradiation or chemotherapy, malnutrition, vitamin deficiencies, steroid use, and certain disease conditions like Crohn's disease are associated with poor anastomotic healing and increased anastomotic leak rates. Septic shock can lead to impaired tissue perfusion, decreased collagen systhesis, and eventual anastomotic disruption. Severe malnutrition has also been shown to decrease tissue collagen and thus decrease bursting pressure. Resections for Crohn's disease appear to carry a significant risk of anastomotic dehiscence from 2–12% (12). Smoking was found to be associated with an increased risk of anastomotic leakage, as was heavy alcohol consumption (13). Inverting the cut edges of bowel in colorectal surgery is also of importance. In one study, the rate of fecal fistula formation was far higher in the group that had everted suture anastomosis (43%) than in the group with inverted suture anastomosis (8%) (14). In animal studies, everted anastomosis have increased leaks and adhesion formation (15). Recent studies have also suggested that hypothermia can result in vasoconstriction, tissue hypoxia, and reduced bacterial killing — all of which can lead to increased infection and leakage rates (16).
For elective anastomosis of the colon and rectum, it is traditional to cleanse the large bowel prior to surgery. The rationale being that decreasing the bacterial load in the large bowel facilitates anastomotic healing and minimizes the consequences of anastomotic leakage. Recent studies have questioned this approach, and there is increasing evidence that a bowel preparation may not be essential and that it may actually be harmful. A Finnish randomized prospective study published in 2000 was first to indicate that patients with bowel preparation had no benefit in leak, infection, or restoration of bowel function rates (17). Subsequent studies have showed that rates of both anastomotic leakage and wound infection were actually significantly higher in the patients receiving bowel preparation compared to those that did not (18). This may be related to the change in native intestinal flora after bowel preparation.
ANASTOMOTIC TECHNIQUES
The two most commonly used anastomotic techniques are: (A) handsewn sutured anastomosis and (B) stapled anastomosis. Prospective, randomized trials have not demonstrated any differences between stapled and hand-sewn anastomosis in terms of in leakage rates, length of hospital stay, or overall morbidity (19). However, controversy remains regarding which of the two methods of creating an anastomosis yields better clinical outcomes. Intestinal segments can be sewn together with various suture materials. The ideal suture material is one that causes minimal inflammation and tissue reaction, while providing maximum strength during the lag phase of wound healing. Popular choices include polyglactin, polydioxanone, and silk. There is little difference between absorbable and nonabsorbable sutures with respect to the strength of the anastomosis. Either continuous and interrupted sutures can be used in performing an intestinal anastomosis. No randomized trials have addressed the question of whether interrupted sutures have a significant advantage over continuous sutures; however, retrospective reviews have not demonstrated any advantage of one method over the other (20). Double layered anastomosis typically consist of an inner layer of continuous or interrupted absorbable sutures and an outer layer of interrupted absorbable or nonabsorbable sutures. Single layered anastomosis consist of one layer of interrupted or continuous absorbable sutures. A 2006 meta-analysis analyzing 670 patients concluded that there was no evidence that two-layer anastomosis yielded a lower rate of postoperative leakage than single-layer anastomosis (21).
CONCLUSION
Anastomotic techniques have greatly improved over the past two centuries, and postoperative complications have fallen accordingly. The principles of successful intestinal anastomosis are: well nourished patient with no systemic illness, no fecal or purulent contamination, adequate exposure and access, gentle tissue handling, well vascularized tissues, absence of tension and distal obstruction, approximation of well vascularized cut ends of the bowel, and meticulous surgical technique. After any anastomosis a close visual inspection of the entire circumference of the anastomosis should be performed. One of the most important determinants of outcome after intestinal anastomosis is careful attention to detail.