Small Animal Surgical Emergencies. Группа авторов

are relatively fixed in position due to their attachments to the mesoduodenum and mesocolon. The descending colon is the longest and most mobile segment of the large intestine [2].

The colon receives its blood supply from branches of the cranial mesenteric artery, except for the aborad half of the descending colon which is supplied by branches of the caudal mesenteric artery (Figure 10.1) [3]. The blood supply to the colon is distinct from that of the small intestines in that arteries enter the colonic wall via short branches known as vasa recti. Venous drainage is by way of the portal vein [2].

Signalment and Clinical Presentation

      Colonic torsion has been infrequently described in dogs. The majority of patients are large breeds and young to middle aged [1]. The most common clinical signs associated with the disease include vomiting, depression, inappetence, and diarrhea, with or without tenesmus. Less commonly, dogs can present in hypovolemic shock with marked abdominal distension and/or pain [1, 4, 5, 6]. Colonic torsion has been described in dogs with previous gastric dilatation‐volvulus that underwent gastropexy. In approximately half of these cases, large intestinal entrapment and strangulation around the previous gastropexy site was found at the time of abdominal exploratory surgery [7].

Diagnostics

Radiographs are the most readily available and useful imaging modality for diagnosing colonic torsion. Common findings include segmental distension of the colon, focal narrowing of the colon, displacement of the cecum, and/or displacement of the descending colon [4]. Typically, there is mild to no small intestinal distention. Barium enema can be useful in making a diagnosis of colonic torsion, as it more clearly highlights focal colonic narrowing when compared to survey radiographs (Figure 10.2).

Computed tomography (CT) has also been used to diagnose colonic torsion in canine patients. Displacement of the colon and cecum, segmental distension and focal narrowing of the colon, and distension of the mesenteric vasculature were common findings. The presence of a “whirl sign” (rotation of the mesentery around its vessels) was another consistently reported CT finding [8].

Figure 10.1 Blood supply to the colon. The majority of the colon receives its blood supply from branches of the cranial mesenteric artery. The most aborad descending colon receives its blood supply from branches of the caudal mesenteric artery. Note how arterial branches penetrate the colonic wall via short, irregular branches (vasa recti).

Figure 10.2 Right lateral abdominal radiograph following barium enema. Coning and complete attenuation of the barium column at the level of the mid‐descending colon can be seen. No barium was noted to reach the transverse or ascending colon which are gas dilated. This is diagnostic for a colonic torsion.

Emergency Stabilization

Successful management of colonic torsion requires prompt diagnosis and aggressive pre‐operative stabilization. At the time of intravenous catheter placement, blood should be collected for a complete blood count and serum biochemistry panel. A coagulation profile should be considered in patients with signs of sepsis. Acid–base status, electrolytes, and serum lactate concentration should be measured and used to guide resuscitation efforts. In addition to the abdominal imaging used to make a diagnosis of colonic torsion, thoracic radiographs are recommended, particularly in older patients (to rule out nodular pulmonary disease) or patients with a history of vomiting (to evaluate for aspiration pneumonia). Patient heart rate, respiratory rate, and pulse quality should be frequently assessed; and blood pressure and electrocardiography monitoring should be initiated.

      Hypovolemia is corrected with intravenous crystalloid therapy (20–30 ml/kg given over 15–20 minutes, repeated as necessary based on patient clinical status). Early pain control should be considered in patients with abdominal discomfort. The author prefers an opioid analgesic (methadone 0.1–0.2 mg/kg intravenously, IV, or fentanyl 2–5 μg/kg IV). A combination of cefazolin (22 mg/kg IV) and metronidazole (10 mg/kg IV) or cefoxitin (30 mg/kg IV) is recommended in anticipation of colonic surgery due to the likely contaminants in this region of the intestinal tract (coliforms, anaerobes). The first dose of antibiotics should be administered approximately 30 minutes before the surgical incision is made; dosing should be repeated every 90 minutes intraoperatively. For patients diagnosed with colonic perforation and septic peritonitis preoperatively, broad‐spectrum antimicrobial therapy should be initiated as soon as possible (ampicillin and sulbactam 30 mg/kg IV, enrofloxacin 10 mg/kg IV, and metronidazole 10 mg/kg IV is a common protocol).

Surgical Management

Emergent exploratory surgery is necessary to reestablish blood flow to the affected region of the colon. A ventral midline abdominal incision is made from xiphoid to pubis. Balfour retractors are placed to improve visualization. A full abdominal exploration should be done, to rule out concurrent abdominal pathology, and the entire gastrointestinal tract should be run to locate the site of colonic disease. The vascular pedicle supplying the affected region of the colon should be carefully untwisted, after which colonic viability must be assessed. Findings may range from mild colonic distension and hyperemia (Figure 10.3) to colonic necrosis with perforation. Careful assessment of colonic wall color and thickness, together with the presence or absence of mesenteric pulses, will help the surgeon to determine whether resection is indicated.

      Any ischemic or non‐viable region of colon should be resected. The colon should be carefully packed off from the remainder of the abdomen using moist laparotomy sponges. Any feces present within the lumen of the colon should be milked orad and aborad, away from the resection site, and kept in place by non‐crushing forceps (Doyens) to minimize the risk of contamination during the procedure. The author recommends placing the non‐crushing forceps approximately 3 cm orad and aborad to the line of transection to facilitate the anastomosis procedure. Crushing (Carmalt) forceps are placed to isolate the length of colon to be resected. Ligation of individual vasa recta supplying the wall of the colon to be resected, rather than ligation of the main vascular branches, is recommended to help preserve blood supply to the remaining bowel. This can be done with small monofilament suture material, a vessel sealing device, or hemoclips. After resection of the non‐viable colon, anastomosis is performed. The author prefers a sutured anastomosis with either 3‐0 or 4‐0 polydiaxonone. Simple interrupted sutures should be placed at the mesenteric and antimesenteric borders, making sure to engage the submucosa which serves as the holding layer. Due to mesenteric fat obscuring the view of the bowel wall, it is recommended that all sutures along the mesenteric border be preplaced prior to tightening. Subsequently, the sides of the anastomosis are sutured with a simple interrupted or simple continuous, appositional suture pattern. The site should be leak tested with a 25‐gauge needle and sterile saline to assess for any overt suturing errors. The rent in the mesocolon is sutured closed with 4‐0 monofilament absorbable suture material in a simple interrupted or continuous pattern.

Figure 10.3 Intraoperative photograph of a colonic torsion. A 180‐degree torsion of the mesocolon was identified (white arrow). The colon orad to the torsion was gas dilated but