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Surgical Options and Prognosis for the Colicky Foal
V.L. Cook
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Take Home Message
The gastrointestinal tract of foals is fragile and great care should be taken to follow Halstead’s principals when performing colic surgery in a foal. Outcome is directly related to the age of the foal and the type of lesion, with young foals and ischemic lesions having the worst prognosis. These results are likely to be directly attributable to postoperative adhesion formation. Laparoscopic adhesiolysis should be routinely considered as a follow up technique in foals that have had strangulating intestinal lesions.
Special Considerations for Celiotomy in Foals
Tissue Handling
The intestinal tract of foals requires extremely gentle handling and the intestine should be kept moist at all times. This is critical to reduce serosal friction and hence reduce intestinal inflammation. Attention should be paid to remove all powder from the gloves by rinsing prior to entering the abdomen. Supple plastic sleeves should be used rather than stiffer plastic ones commonly used in adults. Hyaluronic acid provides excellent lubrication for handling the small intestine. One or two vials can be placed in a bowl and the surgeon’s finger tips periodically coated with it to reduce friction while running the small intestine. The gastrointestinal tract is extremely friable and jejunal mesenteric tears occur easily and are difficult to repair as the mesentery tears during suturing. Therefore care should be taken when handling distended small intestine in foals to reduce mesenteric tension.
Adhesions
It is estimated that approximately 33% of foals that have colic surgery develop adhesions.1 Adhesions form when there is inflammation of the peritoneal mesothelial cells, which occurs from surgery, ischemia or peritonitis. This results in the exudation of serum containing fibrinogen onto the surface of the intestine. Fibrinogen is converted to soluble fibrin by thrombin, and then to insoluble cross linked fibrin by clotting factor XIIIa (fibrin stabilizing factor) to form fibrinous adhesions. Normally, fibrinolysis occurs in which fibrin is broken down into fibrin degradation products by plasmin. Thus, most fibrinous adhesions are resolved by this mechanism. However, if fibrinolysis is reduced, as occurs in sepsis and inflammation, an influx of fibroblasts occurs and collagen is deposited, resulting in a permanent fibrous adhesion forming. The reasons that foals are more prone to adhesions than adults are unclear but preliminary data from Cornell suggests that foals with gastrointestinal disease have much higher levels of fibrinogen and decreased fibrinolysis in the abdomen than healthy foals (S. Fubini, personal communication).
In addition to careful tissue handling, several techniques can be used which may reduce the incidence of adhesions in foals. First, and most importantly, simply ensuring that the foal is treated with broad spectrum antibiotics and an NSAID may reduce inflammation and abdominal sepsis and hence reduce adhesion formation. In an experimental study no adhesions were formed in foals treated with potassium penicillin, gentamicin and flunixin meglumine compared to adhesions forming in 5/6 foals if no treatments were given.2 The effect of a COX-2 selective NSAID has not been evaluated. Additionally, the same study showed benefit of low dose (20mg/Kg) DMSO IV BID. Subcutaneous heparin and intraperitoneal carboxymethylcellulose were not as effective in preventing adhesions from forming.2 In addition because of the possibility of omental adhesions, it is advised to remove as much of the omentum as possible before closing the abdomen.
Foal Specific Surgeries
Ruptured Inguinal Hernia
Although performed on an emergency basis, these surgeries have an excellent prognosis. Resection of the small intestine is usually not necessary because the inguinal rings are large and rarely cause strangulation the intestine. The key to correcting these is to reduce the hernia prior to making an incision or even prepping the foal. It is best achieved once the foal is anesthetized and placed in dorsal recumbency. The hind legs are then lifted and then gently shaken until all the intestinal contents have returned to the abdomen. Surgery is then very straightforward and consists of a unilateral closed castration of the affected side and careful closure of the superficial inguinal ring. If the hernia is irreducible a midline laparotomy incision must be made in order to return the affected intestine into the abdomen. In these situations a resection is more likely.
Strangulating Umbilical Hernia
This problem is usually seen in slightly older foals. Diagnosis is easily made based on the presence of a painful non-reducible umbilical hernia. Distended small intestine may also be seen on the ultrasound examination due to outflow obstruction. It is usually the anti-mesenteric surface of the ileum that is entrapped in the hernia and this is called a Richter’s hernia. If such a hernia is left untreated it can rupture and dissect subcutaneously or form an enterocutaneous fistula. However, if treated promptly these cases have an excellent prognosis because it is rare for the blood supply to the entrapped ileum to be compromised and so these cases usually do not require an intestinal resection. Correction is easily achieved by incorporating the hernia ring into the midline incision to release the entrapped intestine and then decompressing the small intestine into the cecum. The hernia is then corrected during routine midline closure.
Gastroduodenal Outflow Obstruction
Surgery to correct an outflow obstruction is not usually performed as an emergency. An excellent understanding of the anatomy is essential to ensure correct orientation of the bypass. A nasogastric tube should be placed prior to induction of anesthesia. Surgical preparation should be done so that the incision can be created up to the xyphoid. The suspected site of the obstruction can be confirmed by palpating and visualizing the duodenum and pylorus once the abdomen is opened. The small intestine is decompressed into the cecum and gas removed from the stomach with a needle and suction. If the pylorus or very proximal duodenum is involved, a gastroduodenostomy is performed between the stomach and distal duodenum using a 2-layer hand sewn side to side anastomosis.3 If the duodenum is involved more aborally, a gastrojejunostomy is performed between the stomach and the jejunum oriented with the oral jejunum on the left side of the abdomen and the aboral portion to the right of the abdomen.3,4 Again a 2-layer hand sewn side to side anastomosis is performed. Additionally, a jejunojejunostomy is usually performed to prevent a stagnant loop forming.3 [...]
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