Prevention of Anastomotic Leaks in Bariatric Surgery

| March 22, 2010

by Aydin H. Pooli, MD, and Edward H. Phillips, MD, FACS

Dr. Aydin H. Pooli is Research Fellow, Cedars-Sinai Medical Center, Los Angeles, California. Dr. Phillips is Vice Chair, Department of Surgery, Cedars Sinai Medical Center, Los Angeles, California

Bariatric Times. 2010;7(3):8–13

There was no funding for the development of this article.

Drs. Pooli and Phillips have no financial disclosures relevant to the content of this article.

Abstract
Anastomotic leak is a major problem complicating bariatric surgery and is associated with increased rates of operative morbidities, mortality, and prolonged hospital and intensive care unit stay. This review, after a comprehensive medical data search, discusses pre-, intra-, and postoperative interventions that can possibly decrease leak rate and their level of evidence.

Introduction
Few professional outcomes are as satisfying as seeing your postoperative bypass or sleeve patient in the hall walking, afebrile, pain free, and tolerating liquids the day after surgery. Conversely, nothing is as disappointing as an anastomotic leak after a good operation. Thank goodness leaks do not happen often. When they do, they can be attributed to the preoperative status of the patient, site of surgery, presence of contamination, technique of the procedure, type of sutures, devices used, technical errors, and even the experience of the surgeon.

The incidence of reported anastomotic leaks varies dramatically.[1–6] Anastomotic leak after bariatric surgery has been reported to be between 0.1 to 6 percent for gastric bypass and 0.7 to 3.3 percent for sleeve gastrectomy.[5,7–9] Overall, bariatric surgery can be performed safely with 90-day mortality as low as 0.35 percent;[10] however, once a leak occurs, mortality rate can be as high as 16 percent.[3] But surgeons do not need to read an article to understand the consequences of a leak: increased suffering, morbidity, increased resource utilization, prolonged hospital stay, disability, mortality, and legal exposure.

The question remains: Can preoperative, intraoperative, and postoperative interventions prevent anastomotic leak in bariatric surgery?

Physiology of Anastomotic Healing
Before preventive interventions can be put in perspective, it is important to have a basic understanding of how the body removes injured tissue and creates new tissue to heal an intestinal anastomosis thus re-establishing bowel continuity. These steps have traditionally been separated into three overlapping phases of wound healing to facilitate learning. The three phases are as follows

1.    Inflammation or “lag” phase: This phase starts with clot formation, deposition of platelets, release of cytokines, vasoactive chemicals leading to collagenase activity, permeability of vessels, and migration of inflammatory cells into the wound (first neutrophils and then monocytes and macrophages). The risk of anastomotic dehiscence and leak is greatest during this phase. It is partly attributed to increased collagenase activity, which can be affected by other factors such as infection. Microbial collagenase has been shown to be responsible for dehiscence in some situations.[11] Collagenase activity does not have as significant a role in cutaneous wounds as it does in anastomotic wounds.[12]

2.    Proliferation phase: This usually begins by Day 4 if there are no factors delaying it. It is manifest when fibroblasts predominate at the wound site; collagen rich granulation tissue is produced by fibroblasts and angiogenesis occurs to supply oxygen and essential nutrient material. Tissue oxygenation, vitamin C, iron, and nutrient supplements are key elements for healing in this phase. “Late” anastomotic leak can occur during impairment in this phase.

3.    Remodeling: The number and density of fibroblast and inflammatory cells (macrophages) reduces and granulation tissue undergoes remodeling and thick collagen fibers and contractile units replace thin fibers. Leak does not usually occur during this phase.[13,14]

Anatomy of Healing
Aanastomotic healing can best be understood in the context of the anatomy of intestine. All four layers of the gastrointestinal (GI) tract (mucosa, submucosa, muscularis propria, and serosa) play an important role in restoring continuity following anastomosis. Apposition of mucosa seals the gap and provides a barrier to luminal contents and bacteria. Submucosa contains the blood vessels, lymphatics, nerve fibers, and the bulk of collagen fibers. The stapled or sutured collagen fibers in this layer provide most of the tensile strength of the anastomosis. Decrease in numbers and the integrity of collagen fibers can lead to anastomotic disruption and leak; on the other hand, significant increase of collagen content especially in muscularis mucosa, which is mostly intermixed with smooth muscles, may result in stricture and chronic obstruction.[12,13,15] Good apposition of serosa provides another protective layer of thin connective tissue and minimizes the probability of the leak by providing epithelial cell migration.[12]

Blood Supply, Tissue Perfusion, and Oxygenation
The next piece of the puzzle is the arterial, capillary, venous, and lymphatic system. Microcirculatory blood flow at the level of the anastomosis is critical to healing. It supplies micronutrients, oxygen, inflammatory, anabolic cells, and growth factors. Disruption of blood flow to the anastomotic area has been shown to lead to anastomotic dehiscence and leak. Tissue oxygenation is dependent on vascular supply to the tissue, arterial oxygen pressure (pO2), and integrity of the microcirculation. Tissue oxygen requirements of a gastric anastomosis have been shown to exceed those necessary for gastric viability.[16]

One study compared blood flow to the gastric fundus and mucosa intra- and postoperatively. There was a significantly lower postoperative blood flow volume (tissue blood flow corrected for hematocrit) in those patients with leak compared to those without. Although hypoxia will stimulate angiogenesis, the healing process will not proceed without tissue O2 levels of 35mmHg or greater. The formation of mature collagen fails when tissue oxygen tension falls below 35mmHg. Angiogenesis, growth factors, and epithelialization are all impaired in oxygen levels below 10mmHg.[13] Thus, cardiac output, arterial oxygenation, oxygen carrying capacity, normo-volemia to prevent visceral shunting, normal tension and minimal trauma to the tissue should be maintained to ensure that local perfusion of anastomotic area is the very best possible.[17]

Systemic Factors Influencing Anastomotic Healing
Systemic factors can also prevent anastomotic healing. They work either by interrupting local tissue perfusion or impairing cellular and molecular proliferation.

Comorbidities, such as cardiac failure, peripheral vascular disease, renal failure, and diabetes, may cause hypoperfusion of the anastomotic site while chemotherapy, radiation, and cofactor deficiency (vitamin and trace elements) act on cellular function, proliferation, and the repair mechanism.

Vitamins A, C, and E are essential factors of wound healing.[2,18] Zinc deficiency delays cell proliferation and the quality of wound healing in the GI tract by increasing the matrix metalloproteinase activity and changing collagen-type ratio.[14,18–20] Patients with noncontrolled diabetes have decreased macrophage number and activity that can lead to reduced angiogenesis, lymphatic vessel formation, and collagen synthesis that lead to delayed healing.[21]

Chemotherapy suppresses bone marrow, causes lymphocyte and monocyte dysfunction and deficiency, and impairs cellular proliferation in the inflammation phase. Glucocorticoids inhibit fibroblast collagen synthesis and impair macrophage and neutrophil migration and function. Radiation results in impaired fibroblast function and proliferation in addition to arteriolar fibrosis, which decreases oxygen delivery and diffusion.[2,11] Table 1
Shows the summary of local and systemic factors that adversely influence anastomotic healing.

Measurement of Gastrointestinal Anastomosis Strength
While there are many ways to measure the various elements in the healing process, the GI anastomosis is generally measured by using the surrogate method of measuring anastomotic strength by quantifying bursting and breaking pressure. Bursting pressure is the maximum intraluminal pressure at burst when inflating anastomosed segments. It is lowest during the first 3 to 4 days following the anastomosis. Then, anastomotic strength is restored rapidly.[13,18,22]

Prevention of Leak
Although the incidence of anastomotic leak in bariatric surgery is low, it is still devastating. The cause is probably multifactorial but what can we do to decrease the incidence? Table 2 shows some interventions to reduce leak rate and their level of evidence.

Preoperative measures. Patients who undergo bariatric surgery usually have multiple comorbidities, such as diabetes, hypertension, poor nutrition, less exercise tolerance, and sleep apnea. All factors that improve intestinal blood flow and oxygen carrying capacity should be optimized preoperatively. These include anemia, iron, cardiac function, sleep apnea, peri-operative hydration to prevent hypoperfusion and hypotension during induction and operation. Elements that effect healing, such as dietary support to supply essential nutrients (protein, zinc, copper) and vitamins (A, C, E) should be replaced if there are deficiencies. Poor control of diabetes can also adversely effect healing and HgbA1c should be stable and less than six percent prior to surgery. Also weight reduction prior to surgery may decrease liver size and don’t forget to arrange for a good assistant on difficult cases (e.g., men with high BMI, revisions, prior surgery). If you are still in your learning phase, delay these difficult cases. Also, make sure that you have good working laparoscopic equipment. While this seems obvious, we are going to discuss the level of evidence of these maneuvers.

Obstructive sleep apnea and leak. The risk of leak increases in patients with obstructive sleep apnea (OSA).[3,23] The mechanism is not clear but it may be a pressure-related phenomenon and related to patient characteristics and not OSA per se. For example, OSA is observed more commonly in central (android) patterns of obesity, i.e., in men with high body mass index (BMI). Technical challenges may contribute to the increased risk of leak in this subpopulation of the patients.[3] Managing OSA with continuous positive airway pressure (CPAP) postoperatively theoretically may increase the risk of leak by means of increasing gastric intraluminal pressure.[23] However, studies have demonstrated that the use of CPAP after bariatric surgery does not result in increased risk of leak and is unrelated to the integrity of the anastomosis. Statistical analysis failed to find a correlation between CPAP utilization and the incidence of leak. Therefore, CPAP is considered a useful modality in taking care of hypoventilation before and following RYGB without increasing the risk of postoperative anastomotic leak.[24,25]

Glycemic control and leak. Postoperative complications are significantly more common among those patients with poor glycemic control and high HbA1c levels (HbA1c>6%). In addition, when HbA1c levels were compared with values less than six percent representing ideal glycemic control, no specific HbA1c levels have shown a higher chance for complications.[26] In these studies, leak rate was higher in patients with HbA1c more than six percent, though it did not reach statistical significance due to the power of the studies.[26,27]

Preoperative weight loss. Morbid obesity is frequently associated with steatohepatitis, which can result in an enlarged liver. Nearly one-third of patients with morbid obesity have fatty infiltration in more than 50 percent of the hepatic cells. Two weeks of preoperative low-energy diet can help reduce the size of the liver in both length and depth and, therefore, afford better visualization of the operative field[28] and consequently could result in a technically superior anastomosis. However, there are no randomized controlled data to support this.

Topical decontamination. It is documented that bacterial infection can cause microcirculation failure and increase collagenase activity.[29] A randomized, controlled trial (RCT) of placebo and decontamination of the GI tract with specific antibiotics pre- and postoperatively in patients undergoing total gastrectomy for cancer showed that there was a significant reduction in anastomotic leak in the antibiotic decontamination group (3% vs. 11%, p=0.049).[30] This is an intriguing concept and a well-designed RCT should be performed in bariatric patients.

Intraoperative measures. Choice of operative technique (open, laparoscopic), surgeon’s experience, technique of anastomosis (hand sewn, stapling), implementation of a well constructed gastric pouch, jejuno-jejunostomy or gastric sleeve, staple line reinforcement (buttressing, over sewing the staple line, fibrin sealant), hemodynamic stability, oxygenation, and intraoperative leak tests are factors that can be altered intra-operatively.

Surgeon’s experience. Studies have shown that surgeons with basic laparoscopic skills usually require a learning curve of approximately 100 cases in order to decrease the complication rate and operation time in laparoscopic gastric bypass.[31–34] In a study by Fernandez et al,[23] the overall leak rate for RYGB was reported to be 6.8 percent in their first 102 cases, which dropped to 1.8 percent in their next 164 patients.[23] Others reported a steady reduction of adverse results in consecutive laparoscopic gastric bypasses with zero leak and mortality in the last year of their study.[35] Therefore, outcome of laparoscopic bariatric surgery improves with experience and can be minimized by transferring skills to surgeons in an academic setting.31 The learning curve in laparoscopic bariatric surgery is one of the longest in its category.[32,33,36] By leveling the learning curve and dividing it to stages (assisting, exposure, and sequencing all steps), one can become proficient in bariatric surgery with minimal morbidity and mortality. Our group found a decreasing trend for operative duration, length of stay, and complications across the different stages of learning curve for RYGB (p<0.05).[31]

Obviously, the technical aspects of performing bariatric surgery is paramount in reducing leaks. The procedurally important aspects are too numerous to discuss in this article, but the proper construction of the Roux limb, gastric pouch, and jejunojejunostomy each have their own mechanical challenges. The Roux limb should be well perfused and tension free, which can usually be accomplished by jejunal division further distal to the ligament of Treitz than by just dividing the jejunum at 15cm each time. The utilization of a retrocolic approach may occasionally be necessary in the patients who have severe central obesity. Acute postoperative small bowel obstructions can be limited by properly constructing the jejuno-jejunostomy and closing the mesenteric defects. Ischemia of the pouch can be limited by the type of dissection and energy source used. The proper sizing of the pouch, especially at the gastroesophageal (GE) junction is important as well. In the creation of the gastric sleeve, it is crucial not to narrow the sleeve at the incisura so as to avoid partial obstruction and increase in the intra-gastric pressure proximally. Given the skill set and experience of the operating surgeon, the following factors can also modulate the leak rate:

Training level of the assistant. Among many factors influencing operative outcomes and postoperative complications experience, the training level and skill of the surgical assistant are least considered. Performing bariatric surgery with inexperienced operative assistants increases operative time.[37] A retrospective study[38] analyzed patients undergoing RYGB in an academic center and found that operating with experienced assistants improved efficiency and decreased complications and readmission rates.[38] Hence, getting an experienced assistant, especially in difficult cases, such as higher levels of BMI and patients with several comorbidities, may reduce leak rate. However, a well-designed RCT is needed to prove this point.

Laparoscopic or open technique. Data from the University Health System Consortium on all patients who underwent laparoscopic or open RYGB for treatment of morbid obesity between 2004 and 2006 (n=22,422) showed that laparoscopic gastric bypass patients had a lower overall complication rate, a lower leak rate, and a lower rate of 30-day readmission compared with open gastric bypass patients.[39]

Hand-sewn or stapled anastomosis. The speed, reproducibility, and ease of use of stapling devices have made them the most frequently utilized technique of anastomosis. Proposed benefits from a stapled technique include better blood supply, reduced tissue manipulation, less edema, uniformity of apposition, and adequate lumen at anastomotic site. These factors are believed to facilitate healing of the anastomosis. There are many systematic reviews showing that both hand-sewn and stapled anastomosis are equally effective in different parts of GI tract. Circular stapling devices are associated with a higher incidence of stricture, but otherwise stapled and hand-sewn anastomosis are identical in outcomes.[40–44]

While there are no significant differences in anastomotic complications between hand-sewn and stapled anastomosis other than stricture, stapled anastomosis can be performed significantly faster, and while not reaching statistical significance, there is a decreasing trend in anastomotic complication rate as the surgeon gains experience.[45,46]

Stapling and ischemic points. Intraoperative assessment of blood flow in surgical anastomosis areas have shown low oxygen saturation compatible with ischemia in tissue adjacent to the staple line compared with 2cm away from the staple line. A real time, noninvasive tissue probe can probably assist surgeons in identifying points at increased risk of ischemia and complications.[47] Real time probe in animal studies demonstrated that mucosal ischemia does occur after stapling and is not affected by different staple heights.[47,48] There should be at least a 1cm distance between parallel staple lines and also between the circular stapler and the nearest staple line.
Buttressing or staple alone. While there is no proof that leak pressure plays a significant role in humans, most of the literature is replete with studies. Over the years, the initial studies were undertaken with suturing technique, then staple height, formation, and layering, and now buttress material. It has been shown in animal studies that staple height and its relationship to the thickness of intestine are important determinants of leak pressure. Yet, it is not well appreciated that there is a great amount of variability, both in staple height and in leak pressure, in different applications of the same type of staple cartridge.[49] On average, white loads (2.5-mm staple height) have a better leak pressure profile than the blue loads (3.5mm), which in turn have a better profile than the green loads (4.1mm) in animal intestine, while overlapping staple lines does not affect the leak pressure.[49]

Buttressing the staple line with different materials is a way to increase burst and leak pressure. Peri-Strips Dry® (Synovis Surgical Innovations, St. Paul, Minnesota), a permanent bovine pericardial strip, Peri-Strips Dry® with Veritas® Collagen Matrix (Synovis Surgical Innovations), remodelable, nonpermanent bovine pericardial strips, and Gore Seamguard® Bioabsorbable Staple Line Reinforcement (W.L. Gore & Associates, Inc, Flagstaff, Arizona)  synthetic bio absorbable products, are available materials for buttressing staple lines. There are a few prospective RCTs that favor buttressing the staple line using bovine derived biomaterials. For example, reinforcing the gastric staple line with bovine pericardial strips (Peristrips Dry) appears to result in a significant reduction of operative time and the number of endo-clips used for hemostasis.[50–52] Staple lines buttressed with bovine pericardium have been demonstrated to sustain higher mean burst pressure than the conventional nonbuttressed staple lines. Most of the buttressed segments, if they fail, fail away from the staple line, while the nonbuttressed segments tend to fail at the staple line.[53]

Staple lines reinforced with small intestinal submucosa have shown better durability with regards to leak rate and significantly higher anastomotic burst pressure in animal models.[54] This is a bit different when looking at the results of a biodegradable membrane such as Biodesign™ (Surgisis®) (Cook Medical, Bloomington, Indiana). The results in animal RCTs are disparate. Some studies show increase in burst strength pressure of the bowel segment staple line,[55] while in other studies, it appeared to be less effective than bovine pericardial strips.[56] In fact, in animal studies, the addition of Gore Seamguard Bioabsorbable Staple Line Reinforcement acutely improves the burst strength in a gastrojejunal anastomosis but not after one week. Interestingly, stapled-only anastomosis have been detected to have statistically more collagen content at one week than anastomosis supported by Gore Seamguard Bioabsorbable with no difference  in vascularity, adhesions, or inflammation.[57] In summary, there is no level-one evidence that buttressing decreases clinical leak rate in bariatric surgery.

A retrospective study showed that the diameter of the gastric tube in minimally invasive esophagectomy is related to post operative leak rate.[58] They observed a significantly higher leak rate in smaller diameter gastric tubes (28% in 4cm diameter gastric tubes compared to six percent leak in 6cm diameter tubes).[58] This suggests that intraluminal pressure may well play a role in microcirculation, or leak pressure and leak rate. Again, a well designed RCT is needed in bariatric patients to investigate this effect.

Oversewing the staple line. Oversewing the staple line during bariatric surgery is an inexpensive but time consuming technique. Additionally, there are no data that establishes its superiority. One study suggests it might even increase the risk of staple line failure.[55] Studies on oversewing to maintain staple line integrity are mainly level-three evidence and the results are not uniform. Some have stated that oversewing significantly reduces the leak pressure and, therefore, should be avoided,[59] while others have concluded that oversewing successfully prevents staple line bleeding and diminishes the incidence of leak formation.[60] Meta analysis of 11 studies showed that there is no reason to believe that reinforcement by buttress or over-sewing provides protection against leak and the decision whether or not to use it is at the surgeon’s discretion and experience.[61]

Circular stapler vs. linear stapler for gastrojejunal junction. A RCT compared circular and linear staplers in patients with morbid obesity undergoing RYGB.[62] Eighty patients were randomly assigned to two groups in which the only difference was the type of stapler used in gastrojejunostomy. Leak rate and anastomosis fistula were not different between the two groups but stricture was more common in the circular stapler group.[62] On the other hand, a nonrandomized study has shown fewer postoperative complications and faster performance of anastomosis in linear staplers compared to circular staplers in gastrojejunal anastomosis.[63] Both studies suggest that linear staplers are preferable to circular staplers in gastrojejunal anastomosis in terms of decreased stricture formation.

Fibrin glue. The mechanism of action of fibrin sealant is to create a fibrin matrix resembling the normal coagulation cascade. Its sealing property is related to bioadhesive characteristics of the clots. In addition, it contains a plasmin-inhibiting protein called aprotinin which increases the life span of the clots.[64] The efficacy of fibrin sealant in prevention of leak after bariatric surgery has been shown in nonrandomized studies.[65–69] However, prospective, randomized, multicenter, clinical trials have shown that there is no difference in leak rates between fibrin glue and control groups.[70,71]

Omental wrap. Omental wrap is suggested to aid healing and avoid leak of the gastrojejunostomy during RYGB. It is a relatively simple adjunctive maneuver that may minimize the risk of gastrojejunal leak though there are no data to prove its benefit.[72,73]

Intraoperative endoscopic leak test. Intraoperative endoscopy can be used as a diagnostic test. A RCT was conducted to compare endoscopy with air and methylene blue through an orogastric tube (OG) to identify intraoperative leak. They demonstrated that endoscopy is able to detect more intraoperative leaks than OG. Routine use of endoscopy was associated with less postoperative leaks compared to a retrospective control group after laparoscopic RYGB.[74] These results could be related to surgical experience and other factors. In addition, intra-operative leaks detected by endoscopy may never become clinical leaks. A well-designed RCT is needed to confirm its efficacy.

Intraoperative hemodynamic factors. As mentioned previously microcirculatory blood flow is critical in anastomotic healing;[13,14] therefore, it is important to keep the patient euvolumic and normotensive and avoid acute anemia through blood loss to maintain tissue oxygenation at the level of anastomosis.

Postoperative Measures
Maintaining continuous positive airway pressure (CPAP), avoiding anemia, and checking for oxygen saturation levels postoperatively are as important as pre- and intraoperative measures to make sure that microcirculation and oxygen and micronutrient delivery to anastomotic area are not impaired. Since anastomotic leak after bariatric surgery can lead to serious morbidities, devastating consequences, and even death, early detection and diagnosis is essential. Early suspicion and low threshold to perform diagnostic tests play a key role to early detection and management of possible leaks. Placing nasogastric tube (NGT) and topical decontamination of the GI tract during wound healing have been suggested previously as tools to prevent leaks from happening; other postoperative diagnostic tools, such as methylene blue swallow, upper GI series, drain amylase level, and CT scans are usually applied for early detection of leaks.

NGT. The insertion of NGT following abdominal surgeries is intended to prevent aspiration, nausea and vomiting and to possibly protect against anastomotic leak in the foregut surgery patient. A Cochrane review of 33 studies comparing no NGT decompression with NGT use demonstrated that patients with NGT use had later return to bowel function, more thoracic and pulmonary complications, and there was no difference in anastomosis leak rate.[75]

Intragastric pressure and sleeve gastrectomy. Normal intragastric pressure has been shown to increase with coughing to as high as 233mmHg (37mmHg mean) and with vomiting to as high as 290 mmHg (81mmHg mean).[76] In porcine small bowel, median leak pressure with buttress ranges from 63 to 121mmHG depending on staple height.[49] Yehoshua et al[77] showed that in sleeve gastrectomy the mean intrasleeve pressure was 43mmHG (32–58 mmHg range) and that small additional fluid volumes (150cc) result in significant elevation of intraluminal pressure (58mmHg before fluid refluxed into the esophagus). Thus, as patients swallow saliva and the gastric mucosa secretes mucous, the volume/burst/leak pressure ratio of the gastric sleeve staple line may become clinically significant. Certainly, intrasleeve pressure could affect microcirculation and anastomotic failure. A study randomizing NGT decompression would be important.

Summary
The prevention of anastomotic leak in bariatric surgery patients starts with patient selection, carries through the preoperative preparation period, and enters the most critical phase during the performance of surgery. It is even possible that interventions postoperatively may affect leak rate.

Unfortunately, the evidence supporting our common practices does not meet the highest standards of evidence. Until we have that evidence, we should do what seems logical and, whenever possible, enroll our patients in properly powered, RCTs that can answer these questions.

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