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Prevention, Diagnosis, and Management of Anastomotic Leak
Incidence and Consequences of Anastomotic Leak
Anastomotic leak is perhaps the most physiologically significant and psychologically devastating complication that commonly occurs following operations for colon or rectal disease. The reported incidence of anastomotic leak following colorectal surgery has varied from 1% to 30%, largely based on the criteria for diagnosis and the length of follow-up; the highest leak rate is seen with anastomoses involving the distal rectum. Leaks account for one-third of all deaths following low anterior resection, with even higher mortality rates observed with intraperitoneal leaks. Anastomotic leaks are associated with dramatically increased perioperative morbidity and mortality, prolonged length of stay, higher readmission rates, the potential need for multiple operative interventions in a hostile surgical environment and unintended permanent stomas. This results in significantly increased hospital costs and resource use, decreased quality of life, and potentially worse oncologic outcomes.
Definition of Anastomotic Leak
Historically, studies of the incidence and etiology of anastomotic leak have been hindered by a lack of a consensus definition of anastomotic leak. There are a broad array of clinical scenarios that could reasonably be described as representing or caused by an overt or occult disruption/imperfection in the anastomotic site (e.g., postoperative abscess). This has often made comparative analyses between institutions and among surgeons a largely arbitrary and unreliable exercise. In 2010 the International Study Group of Rectal Cancer proposed a uniform definition of anastomotic leak as a defect at the anastomotic site leading to a communication between the intraluminal and extraluminal compartments. This communication can be confirmed radiographically, endoscopically, or intraoperatively. A pelvic abscess in close proximity to the anastomosis is also considered an anastomotic leak. The group also defined the severity of anastomotic leaks based upon the clinical management required. Grade A leaks are those managed without an invasive intervention, grade B leaks are those managed with invasive intervention other than a laparotomy (e.g., percutaneous drainage), and grade C leaks are those requiring laparotomy.
Prevention
Discussion of anastomotic leak prevention has generally centered around risk factors associated with anastomotic leak and/or mechanical means to increase anastomotic strength. Both of these areas of inquiry have contributed to only a limited understanding of the actual mechanism by which leaks occur and how best to prevent them. The reported risk factors vary greatly from study to study, and it can be challenging to know which clinical features are simply associated with a greater tendency for a leak and which may serve as a surrogate for some other factor that is of pathogenic importance.
For decades, studies have focused on the technical aspects of anastomotic creation, considering such issues as sutures versus staples versus compression, single- versus two-layer construction, inverted versus everted technique, and the merits of a wide variety of mechanical devices designed to strengthen or protect the anastomosis, usually finding minimal impact on the incidence of anastomotic leaks. This structural framework of understanding has not appreciably moved the needle in preventing this devastating complication; it seems clear that new paradigms are needed. In this light, the possible role of the microbiome and collagenolytic bacteria in causing anastomotic leaks is intriguing. Certainly the historical admonitions of attention to detail, avoidance of tension, and assurance of adequate blood supply seem prudent, but the fact remains that anastomotic leaks still most commonly occur in anastomoses that have no evidence of ischemia, are under no tension, and have been carefully tested for structural defects.
Preoperative and Perioperative Enteral Nutrition
Preoperative malnutrition has been identified as a major risk factor for anastomotic leaks, whether defined generally by low preoperative serum albumin and total protein or more specifically by weight loss of 10% or more, serum albumin less than 3.5 g/dL, and serum protein less than 5.5 g/dL. Identifying those patients with diminished nutritional status and treating them perioperatively with nutritional repletion may reduce the risk of, and the morbidity and mortality from, anastomotic leakage.
Intraoperative Assessment
Laser Fluorescence Angiography
Adequate blood supply has long been highlighted as critical for proper healing of an anastomosis. Less obvious is the amount of blood flow that represents a critical threshold for adequate healing to occur. Traditionally, perfusion has been assessed through visual inspection for color and bleeding of the cut edges, fluorescein dye angiography with a Wood lamp, or presence of pulsatile flow identified by palpation or Doppler ultrasound. More recently, the use of intraoperative laser fluorescence angiography with indocyanine green dye (ICG-FA) has been used by surgeons to assess tissue perfusion. ICG-FA is performed by administering indocyanine green intravenously, then assessing tissue perfusion with a near-infrared imaging system. Perfusion may be assessed before transecting the bowel or after completion of the anastomosis.
Currently, assessment of fluorescence intensity is subjective, and it may be unclear when a change in the surgical plan is appropriate based on the image. This may be no small matter in selected circumstances, such as a low pelvic anastomosis where further resection to an area of “improved” perfusion may require extensive additional mobilization and potentially result in the unintended consequence of increased tension on the anastomosis. A systematic review of 12 different randomized studies suggested that ICG-FA may reduce the risk of anastomotic leakage; however, given the heterogeneity of study designs and lack of high-quality evidence, the review was considered inconclusive for the existence of any actual clinical benefit. Data assessing the potential benefit of ICG-FA will be forthcoming from a randomized controlled, parallel, multicenter study assessing perfusion outcomes in patients with rectal cancer undergoing a low anterior resection (PILLAR III trial).
Air Leak Test
Air leak testing involves filling the pelvis with warm saline followed by distention of the newly created anastomosis with air. A randomized controlled study supports the use of air leak testing; the leak rate was reduced from 14% to 4%, presumably by identifying and remediating technically imperfect anastomoses. Based upon the results of a large cohort study of 825 patients, patients with positive air leak tests treated with suture repair had higher clinical leak rates (12.2%) than patients who received a diverting stoma (0%) or underwent reanastomosis (0%). The key in this setting is a sober and objective assessment of the problem and the prospects for repair. If a well-localized and clearly defined defect is identified in an otherwise healthy anastomosis, suture repair with repeat testing of the anastomosis is appropriate. However, when exposure is suboptimal and the defect cannot be clearly visualized to enable an accurate repair, the anastomosis should be redone and/or the patient diverted.
Dye Test
A dye test can be performed by injecting a mixture of sterile water and blue dye or povdone-iodine (Betadine) through a large-bore catheter placed transanally, while clamping the proximal bowel. A volume of 180 to 240 mL is usually required to adequately distend the anastomosis. One study has shown that the dye test allowed for the easier detection and localization of leaks than air leak testing.
Endoscopy
Intraoperative endoscopic visualization of the anastomosis allows surgeons to assess for mucosal viability, staple line disruptions, or bleeding and provides the ability to intervene immediately if necessary. Although intraoperative endoscopy provides a useful adjunct to air leak testing, there is currently no evidence that its use alone results in fewer anastomotic complications. As with ICG-FA, objective endoscopic criteria are lacking to assess the quality of the anastomosis and guide intraoperative decision making.
Drains
The use of prophylactic intraperitoneal drains has been extensively debated. An accurate assessment of benefit has been difficult due to variation in the types of drains used, their location, and the duration of their use. There is extensive evidence that draining an intraperitoneal anastomosis is of no benefit. However, as compared with the abdominal cavity, fluid is much more likely to accumulate in the dependent area of the pelvis, and using pelvic drains after low anterior resection may be of greater utility because the nonperitonealized pelvic floor fails to absorb fluid efficiently. However, it remains unclear how effectively pelvic drains manage to remove this fluid and whether they really provide any benefit. Current evidence suggests that routine prophylactic drainage does not reduce postoperative anastomotic complications. Another suggested benefit of placing drains near a pelvic anastomosis is the early detection of an anastomotic leak prior to the onset of symptoms. Unfortunately, many leaks do not present themselves through a surgical drain, and surgeons often remove drains early in the postoperative period, before a leak might manifest itself.
Diverting Stomas
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