Anastomotic Obstruction

The clinical distinction between anastomotic obstructions and postoperative ileus (POI) is difficult, and each can contribute to the pathogenesis of the other (¹). The first causes greater and more persistent signs of abdominal pain (¹). Mechanical obstruction of a small intestinal anastomosis by anastomotic impaction, hematoma, or constriction, arises from errors in technique (¹). In an overzealous attempt to prevent leakage, some surgeons invert intestinal edges excessively or apply more than one layer (¹). Stromas of marginal size are prone to obstruction because they are further reduced by postanastomotic edema (¹). Small intestinal volvulus may develop in distended jejunum and at points of small intestinal fixation, such as at a jejunocecal anastomosis (¹). Risk of this complication is increased in a jejunocecal anastomosis by failure to decompress intestine during surgery (¹).

The most important point for surgeons to consider is that true POI is rare after abdominal surgery and that most horses with postoperative reflux have a surgical complication that reduces small intestinal function (¹,⁴). The diagnosis of POI is made in horses largely based on reflux through a nasogastric tube. Therefore, postoperative reflux is a clinical finding and should be regarded as such in each horse until a cause is established, rather than simply labeling it as POI. Often overlooked in discussions of POI in horses is the contribution from mechanical factors, such as anastomotic obstruction or stenosis, delayed transit through an anastomosis because of motility derangement or interruption across the anastomosis, or failure to adequately decompress distended small intestine during surgery.

In one study, postoperative ileus was purely a function of the type of anastomosis and did not appear to correlate with other findings (³). Of the 16 horses that had gastric reflux after small intestinal surgery, 9 (56%) had a mechanical obstruction that required repeat celiotomy and/or euthanasia (³). The remaining 7 of 16 (44%) were diagnosed as having a functional POI 10% of total (³). Of these 7 horses, 5 had a jejunocecostomy, 1 had no resection, and 1 had a jejunoileostomy. No horse that had a jejunojejunostomy had POI, despite similar clinical presentations and lesions as horses that had a jejunocecostomy (³).

Postoperative reflux can develop after handsewn anastomosis if the surgeon tries so hard to get a leakproof anastomosis that the lumen becomes constricted, especially if a continuous pattern or more than one layer of tissue is used (²). Even slight luminal constriction is poorly tolerated in equine small intestine, and can increase resistance to flow (²). Although most horses probably do develop some degree of postoperative small intestinal paralysis or POI, the tendency to focus on functional disturbances and treat them with prokinetic drugs runs the risk of overlooking other potential causes (⁵). The most common cause of reflux after small intestinal surgery in the author’s experience is a failure to decompress all distended small intestine at surgery (²). Decompression is accomplished by stripping the fluid contents through the strangulated bowel into a bucket (and not into the cecum) (²). Horses are very sensitive to small intestinal distention, and the concerns about handling the bowel during decompression and causing reflex POI are not valid, provided that good technique is used (²).

If postoperative reflux develops, the patient should enter controlled fasting, a nasogastric tube should pass as needed, and the content received should be evaluated. Disturbances in acid-base balance, hydration, and electrolytes are treated through parenteral hydration, and a prokinetic agent is given (Table 1) (²). Response to prokinetic agents and IV lidocaine is inconsistent, and the author does not use these agents routinely after small intestinal surgery (³,⁴).

Adhesions

Horses are not particularly prone to adhesion formation but are extremely sensitive to them (¹). Foals between the ages of 15 days and 6 months are more likely than weanlings or yearlings for developing adhesions requiring surgical intervention (²³). Adhesions usually cause problems in the first 2 months after surgery. Although they can develop at any time, are more likely after small intestinal resection and anastomosis than other procedures, and are unlikely to develop after large intestinal surgery (¹). Factors that could contribute to adhesions are postoperative ileus, ischemia, violations of Halstead’s principles of surgery, foreign material, serosal abrasion by towels, and use of large suture material (¹). After experimental ischemia-reperfusion of the small intestine in foals, gross adhesions were prevented by treatment with a combination of gentamicin and flunixin meglumine or by systemic administration of dimethyl sulfoxide (²³). In one study 1, prevalence of confirmed adhesions was 6%, although inclusion of deaths from colic yielded an estimated prevalence of 13% (³). Prevention by intraabdominal instillation of sodium carboxymethylcellulose (SCMC) (⁶), or application of a membrane of SCMC and hyaluronic acid holds promise (⁷), but clinical trials are inconclusive (⁴).

Miscellaneous Complications of Small Intestinal Surgery

Other reported complications are anastomotic kinks, persistent distention, and pain from failure to decompress distended bowel, anastomotic stricture, mesenteric rents, anastomotic ischemia, and bleeding from mesenteric vessels (⁴,⁸). Anastomotic dehiscence and peritonitis are rare and usually caused by postoperative ischemia and technical error (¹). Failure to effectively ligate mesenteric vessels can lead to postoperative hemorrhage (¹). Fatal hemorrhage can be caused by tearing of the portal vein during the extraction of strangulated bowel from the epiploic foramen (¹), and this can be prevented by withdrawing the strangulated bowel gently through the plain of the opening rather than upwards against the edge of the portal vein (²). Other techniques are also available such as decompression of the entrapped loop, with or without transection on the proximal side, and then oversewing the blind ends. The decompressed oversewn blind end is easy to pull through the foramen (²). Life-threatening intraluminal hemorrhage is a rare complication of jejunocecostomy, characterized by the passage of tarry feces and declining PCV. It is possibly caused by a large bleeding vessel on the cecal side (¹). A rare complication of jejunocecostomy is obstruction of the cecocolic orifice by an ileal stump that has intussuscepted into the cecum and progressed into the right ventral colon (⁹). The risk of this complication can be reduced by making a short ileal stump (²).

Repeated Celiotomy

Repeated celiotomy is a lifesaving procedure and can be required for 19 % of small intestinal diseases (³). Although the distinction between postoperative ileus and mechanical obstruction can be difficult, horses with the latter usually demonstrate a greater amount of pain and have a progressive increase in heart rate (¹). The disadvantages of a second exploration of the abdomen are the expense and risk of incisional site infection, having as a matter of consideration that the patient’s immune system is compromised after any surgical procedure, which diminishes the effects of antibiotics and other drugs such as NSAIDs (¹). However, survival after a repeated celiotomy can reach 64 %, and the benefits of this procedure can outweigh the risks and disadvantages (¹).

Recurrence of Original Disease

Right dorsal colon displacement and entrapment over the renosplenic ligament can be treated by surgical and non-surgical methods, and have low morbidity and mortality rates, but can be recurrent (¹). Renosplenic entrapment can have a recurrence rate of approximately 8 %, which is low, but readily prevented by laparoscopic closure of the renosplenic space (²). Large colon volvulus has a high rate of recurrence, especially in broodmares (¹⁰), which has significant importance due to the high mortality associated with this disease (¹). Colopexy of the ventral colon to the body wall is designed to prevent the recurrence of colon displacements (¹¹), and the same goal is achieved by resection of most of the colon in horses that have a large colon volvulus and compromised colon (¹⁰). Open or laparoscopic closure of the renosplenic space can be used to prevent the recurrence of colon entrapment in this structure (¹).

Cecal impactation can be treated medically or surgically, the latter by typhlotomy alone or combined with ileocolostomy to bypass the cecum completely (with ileal transection) or incompletely (without ileal transection to preserve some ileocecal flow) (¹). This disease has a high rate of recurrence and carries the danger of cecal rupture, which explains why some surgeons instead use a bypass procedure (¹).

Endotoxemia

Large colon volvulus can rapidly cause ischemia and extensive colon necrosis (¹). If resection is not performed, as in a colon that has suffered a mild enough ischemic insult to survive, progressive mucosal damage after surgery can result from continued vascular occlusion and reperfusion injury (¹). If the colon is resected, all affected tissue might not be accessible to allow anastomosis, and any remaining mucosa that sloughs postoperatively can cause endotoxemia, anastomotic leakage leading to peritonitis (¹). Removal of as much strangulated colon as possible could reduce endotoxin access to the circulation by reducing transmural leakage across a large bulk of necrotic mucosa (¹).

Endotoxemia is treated with intravenous fluids and flunixin meglumine, but additional treatment is often warranted (¹²). Such treatment includes Endoserum (Immvac, Inc, Columbia, Mo), a hyperimmune serum from horses vaccinated with Salmonella typhimurium Re mutant (¹). Polymixin B is a cationic polypeptide antibiotic that can bind and neutralize endotoxins and is given to horses for this purpose at a dose of 1000 to 6000 IU/kg body weight intravenously every 8 to 12 hours (¹). At doses of greater than 6000 U/kg, polymyxin B can cause toxic owing to its ability to disrupt phospholipid membranes (²⁶). The risk of kidney damage with this drug could be increased by existing damage or dehydration (¹). Although a crystalloid fluid, such as lactated Ringer’s solution, Plasmalyte A, or Normosol-R, is the mainstay of treatment for fluid and electrolyte deficits caused by endotoxemia, plasma or Hetastarch might be required to increase colloid oncotic pressure in horses with total plasma protein concentrations below 5g/dl (¹). Complications of endotoxemia are laminitis, disseminated vascular coagulopathy, catheter-related sepsis and thrombosis, renal disease, abortion, respiratory disease and myocarditis (¹²).

Peritonitis

Peritonitis is very rare after colic surgery, but theleakage of an anastomosis in the non-viable colon after resection for large colon volvulus is one of the more common causes (¹). Equine peritoneum can handle intraoperative contamination that is removed at surgery, but even slight leakage from a suture line is poorly tolerated (¹). The most common reported pathogens isolated from horses with peritonitis include E. coli, Staphylococcus, Streptococcus, Rhodococcus, Bacteroides, Clostridium, and Fusobacterium spp (²⁵). Enterotomies are often indicated for large colon diseases, such as removal of enteroliths, impacted foreign materials, and feed impactions, but dehiscence of the suture line is extremely rare and usually results from a surgical error (¹). Intraoperative contamination during surgery is usually well contained and removed by copious lavage, and even severe contamination of exteriorized bowel rarely causes peritonitis (¹). Rectal tears that extend through the mucosa and remaining layers, with or without penetration of the serosa or mesentery, can cause severe peritonitis and even fecal contamination of the abdomen (¹). Although not a direct complication of surgery, it can result from preoperative rectal palpation, and should always be considered as a possible cause of peritonitis in the postoperative period (¹).

The surgical procedure that carries the highest risk of peritonitis is colotomy in the right ventral colon for reduction of a cecocolic intussusception, whether or not the necrotic cecum is resected through the colostomy (¹). The severe contamination from this procedure can be difficult to contain during surgery but can be prevented through careful isolation of the colotomy site by drapes or a sterile plastic sheet sutured around the proposed incision (¹).

A focal small colon impaction with an enterolith or dehydrated feed material can cause transmural pressure necrosis (¹). Although the vascular changes at the impaction site are recognizable, it is not unusual for the impacting material to have undergone repeated impaction and spontaneous correction at more proximal segments of the small colon (¹). These sites can progress to full-thickness mural necrosis after surgery and cause peritonitis (¹). Therefore, a careful intraoperative inspection of the prestenotic segment of the small colon is recommended to prevent this mishap (¹).

Miscellaneous Complications of Large Intestinal Surgery

Complications of enterotomy are very rare, but the most common is hemorrhage from the incision edges, which can be severe enough to cause melena and hemorrhagic shock (¹). There is some evidence that an enterotomy, but not a small intestinal resection and anastomosis, can increase the risk of postoperative incisional infections and other incisional problems in the body wall (¹³). Possibly, the high bacterial burden in the colon increases the chances of contamination to the edges of the body wall incision (¹). Obstruction of an enterotomy is possible if the lumen is reduced by excessive inversion, which is why the author places a pelvic flexure enterotomy in the widest part, closer to the left ventral colon (¹).

Incisional Swelling

Postoperative edema, usually in large plaques to both sides of the midline, is usually most evident at 5 to 7 days after surgery (¹). Although severe cases signify a slowly developing infection, edema alone could be harmful by decreasing local oxygen tension in the incision (¹⁶), putting tension on suture lines, weakening the tissues, reducing blood supply, and separating any bacteria in the incision from the immune system (¹).

Incisional Infection

Focal drainage of serum, fibrin strands, or mucopurulent material from an incision, with or without fever, is evidence of incisional infection (¹⁴). The mean time to incisional drainage is 17 days after surgery (¹⁶). Ultrasonography should be used for early diagnosis because it is sensitive and can be used to evaluate the integrity of the infected body wall and to locate abscesses (¹). Risk factors for incisional infection and related complications are horses older than 1 year and that weigh more than 300 kg (¹⁴), enterotomy, increased fibrinogen concentration in the peritoneal fluid, use of polyglactin 910 to close the linea alba (¹³), use of a U suture pattern in the linea alba (¹⁷), incisional contamination in the recovery stall, high numbers of bacterial CFU obtained after anesthetic recovery, poor intraoperative drape adherence, high numbers of CFU obtained from surgery room contamination, preexisting dermatitis (¹⁶). Surgical site infection is a common and important complication that occurs in 7.4 % to 37 % of horses undergoing abdominal surgery for acute gastrointestinal disease (²⁵). Treatment of infection involves removing some skin sutures to establish drainage, and cleaning the incision as often as needed with a dilute antiseptic soap, with or without systemic antibiotics selected by culture and sensitivity testing of exudate (¹). An abdominal bandage and topical antibiotics can be applied if the infection is extensive, but the bandage must be replaced frequently (¹). There is some evidence that an abdominal bandage applied routinely after surgery might reduce the prevalence of incisional infection (¹⁸), but this is expensive and not used by the author. Short surgery times, attention to proper technique and asepsis, short incisions, and application of a protective adhesive barrier over gauze sponges before placement in the recovery stall can prevent infection (¹⁵). Recent clinical trials have demonstrated that right ventral paramedian incision is at least comparable to and possibly better than a ventral midline approach for colic surgery (¹⁹), that skin staples increase the risk of incisional infection (²⁰), and that horses that develop incisional infections usually culture bacteria from the incision within 12 hours of surgery that are resistant to many commonly used antibiotics (¹⁵).

Dehiscence of Body Wall Incision

Dehiscence of the body wall, with or without eventration, is the most serious wound complication following an exploratory celiotomy (¹⁵). The main reasons for wound dehiscence include loss of strength in absorbable sutures, breakage of sutures, knot failure, and tissue failure (¹⁵). Good surgical technique, decompression of all distended bowel, and smooth anesthetic recovery can reduce the risk of partial or complete wound disruption (¹⁵). Severe incisional infections can delay healing and cause tissue necrosis and dehiscence in as little as 5-7 days following surgery (¹⁴,¹⁸). Delayed disruption of a ventral midline incision (3 to 8 days after surgery) is usually preceded by copious drainage of peritoneal fluid and gap formation in the linea alba, followed by prolapse of omentum or bowel (¹⁵). In such cases, the horse should be anesthetized; all suture material removed, and the incision repaired by secondary closure (¹⁵). Acute dehiscence in the recovery stall is more catastrophic because there is little warning, the horse is not easily controlled, and a large amount of bowel is usually prolapsed (¹⁵). Despite the extensive contamination, intestinal bruising, and venous congestion associated with evisceration, resection is rarely needed and the prognosis for full recovery is good, provided self-inflicted trauma is prevented (¹⁵). However, extensive self-inflicted damage to bowel and disruption of mesentery can require resection and anastomosis or euthanasia (¹⁵).

Hernia Formation

Horses with incisional complications have an increased risk of developing hernias, especially those incisions that become infected (¹⁵). Hernias may appear weeks to months after the initial surgery (¹⁵). Hernia repair should be postponed for approximately 3 to 4 months after the first surgery to allow inflammation and infection to resolve fully and for the hernial ring to become firm and well organized (¹⁵). Large hernias can be repaired by suture closure or by mesh (¹⁵).