THE MERCK VETERINARY MANUAL
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Other Common Equine Emergencies

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Esophageal Obstruction

(Choke)

Also see Esophageal Obstruction in Large Animals.

Intraluminal esophageal obstruction is a common emergency in horses and is caused by impaction of ingested feed material. The most frequent sites of impaction are the proximal esophagus and just cranial to the thoracic inlet. Predisposing factors include bolting of feed, poor dentition, recent sedation, poor feed quality, recent feed changes, and dehydration.

Clinical signs of choke include nasal discharge containing saliva and feed material, hypersalivation, coughing, retching, signs of colic, or frequent attempts to swallow. The horse may be observed repeatedly stretching and extending the head and neck. Esophageal obstruction is identified by palpation of a foreign body in the neck, passage of a nasogastric tube, or esophageal endoscopy. In refractory cases, radiography and contrast radiography may be used, particularly if a foreign body, stricture, diverticulum, or esophageal rupture is suspected. Ultrasonography may identify thoracic changes consistent with aspiration of feed.

Once the presence of an obstruction has been confirmed, the horse should be muzzled, and feed and water withheld. Acute, simple obstructions may resolve with sedation and consequent relaxation of the esophageal musculature. An α2-agonist such as xylazine or detomidine provides good muscle relaxation. Oxytocin (0.11 mg/kg, IV) has been demonstrated to provide good esophageal relaxation and has been used to resolve esophageal obstructions. Adverse effects may include mild signs of colic, and this drug should not be given to pregnant mares. The obstruction should resolve within 1 hr after administration of a muscle relaxant. If the horse is dehydrated, IV fluids may also help to resolve the obstruction.

If the obstruction has not resolved within ~1 hour after sedation, or if the choke is chronic (>3 hr duration), the horse should be sedated again to allow the head to drop for lavage of the esophagus. A nasogastric tube is passed, and gentle lavage with water is performed to flush the esophagus. Mineral oil should never be used because of the risk of aspiration pneumonia. An esophageal lavage tube (a nasogastric tube with a cuff) is useful to help resolve the obstruction and reduce feed aspiration. Alternatively, a cuffed endotracheal tube can be passed through the nasal passages and into the esophagus, and a smaller nasogastric tube used for lavage. These procedures can be repeated intermittently and can be aided by general anesthesia. If unsuccessful, an endoscope can be used to identify the obstruction and facilitate manual removal using endoscopic forceps.

After the obstruction has been relieved, endoscopy can be used to assess the esophageal mucosa. Circumferential ulceration can lead to stricture formation with recurrence of obstruction. Horses that have been choked are at risk of recurrence in the 2–4 wk after the initial event, even without visible esophageal damage. Feeding a slurried, pelleted diet or grass can prevent recurrence. When the esophagus has been damaged, narrowing is maximal 30 days after the obstruction. Before attempts are made to resolve a potential stricture, the horse should be managed medically with dietary modification for 60 days to allow for remodeling of the scar tissue. Broad-spectrum antibiotics are administered to prevent or treat aspiration pneumonia, along with anti-inflammatory drugs and tetanus prophylaxis. Sucralfate (20–40 mg/kg, PO, tid-qid) has been advocated to facilitate healing of esophageal ulceration.

Rectal Tears

Also see Rectal Tears.

Rectal tears are serious and possibly life-threatening injuries in a horse. Prevention is key, but if a rectal tear occurs, appropriate and timely referral can result in a successful outcome. Rectal tears are classified into four grades based on the number of layers involved. Grade I tears involve the mucosa and submucosa only; grade II involve the muscularis only, with a mucosal-submucosal hernia; grade III involve the mucosa, submucosa, and muscularis, leaving the serosal layer intact; and grade IV involve all layers of the rectum, including the serosa. In the case of grade III tears, further classification is made based on the location of the tear; grade IIIa tears leave the visceral peritoneal intact, and grade IIIb tears are located dorsally in the mesentery. Most tears resulting from rectal palpation are located dorsally and extend into the mesocolon. Retroperitoneal tears are rare but have been reported. Fecal contamination often occurs with grade IV tears, but bacterial translocation and peritonitis is still possible with grade III tears.

A rectal tear is suspected when there is sudden loss of resistance during palpation and when a copious amount of fresh blood is present on the rectal sleeve. Blood-tinged mucus usually indicates mucosal irritation only. If a tear is suspected, the severity should be immediately assessed and measures taken to initiate treatment or referral.

The horse should be sedated for assessment of the tear, and an epidural performed if there is any straining. N-butylscopolammonium bromide (0.3 mg/kg, IV) may be given to decrease peristalsis. A lidocaine enema may also reduce straining. A speculum should not be used, because it can worsen the tear. Digital palpation (preferably bare handed) is then carefully performed. A thin flap of tissue indicates a tear through only the mucosa. If a large cavity with a thin membrane is noted, a grade III tear is present. If intestine can be palpated, the tear is a grade IV. Visual confirmation can be made carefully using colonoscopy.

Grade I and II tears can be medically managed with antibiotics, a laxative diet (mineral oil, mashes of complete pelleted feeds or alfalfa pellets, fresh grass) and analgesics (flunixin meglumine) to facilitate defecation. Select grade III tears can be managed similarly, if necessary because of financial restrictions, but also require daily manual evacuation for up to 3 wk. Peritonitis is a risk, repeat epidurals are required, and the time commitment is substantial. For the best outcome, grade III and IV tears should be referred to a surgical facility. However, it is essential to prevent fecal contamination of the abdomen during transportation; therefore, rectal packing is highly recommended. The horse is sedated and an epidural performed using a combination of xylazine and mepivicaine. A tampon composed of a 7.5-cm stockinette filled with moist, iodine-soaked cotton, coated with surgical lubricant is inserted until it is located at least 10 cm cranial to the tear. The stockinette should be inserted before filling it completely to avoid enlarging the tear. The anus is then temporarily occluded with a purse-string suture or towel clamp. The horse should be given systemic, broad-spectrum antibiotics, NSAIDs, and appropriate tetanus prophylaxis. Prevention of fecal contamination by grade III and IV tears during referral has a direct influence on the success of the outcome.

At the referral facility, the tear is reassessed to identify additional damage sustained during transportation. An abdominocentesis is performed to check for peritonitis. After assessment, several treatment options are available. For grade II tears with no fecal contamination that are at risk of forming a diverticulum, primary repair using a rectal approach can be attempted using one-handed sutures. The horse should be monitored carefully for development of a perirectal abscess, which will require surgical drainage. For retroperitoneal tears with fecal contamination, the tear can be packed with iodine-soaked gauze and the cavity cleaned out daily. In mares, the cavity can be drained into the vagina, and the tear closed primarily. A laxative diet and analgesics are provided to decrease the pain of defecation. The most serious complication of retroperitoneal tears is development of an abscess that migrates forward into the abdominal cavity. This is prevented by ensuring appropriate drainage into the rectum or vagina.

For grade III or IV tears in a caudal location, primary repair using sutures through a rectal approach can be attempted. A successful repair of a grade IV tear using a linear stapling device has been reported. This approach requires that the abdomen has minimal to no contamination. Alternatively, these tears can be treated through a ventral midline approach, followed by an antimesenteric incision in the caudal small colon and repair through the lumen. A celiotomy has the advantage of a large-colon enterotomy and lavage, thus reducing the fecal load on the suture line.

Grade III and IV tears can also be treated by insertion of a rectal liner using a ventral midline celiotomy. Rectal liners are made of a plastic ring glued to a rectal sleeve. The liner is introduced rectally by a nonsterile assistant and sutured to the small colon using an external circumferential suture pattern that allows the ring to slough in ~10 days, resulting in a small-colon anastomosis. The liner diverts the normal fecal passage until the tear has healed. In other cases, a loop colostomy can be performed to maintain patency of the distal segment. The colostomy is performed as the first step; after the tear has healed, colonic continuity is reestablished using a second surgical procedure. In all fecal diversion procedures, an attempt is made to close or approximate the tear. Laparoscopic suturing of rectal tears has been described experimentally.

Postcastration Evisceration

Postcastration evisceration is always a risk after open castrations, but the risk is increased in draft horses, in Tennessee Walking horses and Standardbreds (because of their larger inguinal rings), or after castration of an adult stallion. Evisceration typically occurs within 4 hr of castration, but is a risk for up to 6 days after surgery.

Evisceration of omentum or small intestine is first identified by a structure hanging out of the surgical incision. It is important to instruct the owner to keep the horse quiet and to support the eviscerated structure(s) with a towel to avoid further stretching or damage. Examination quickly reveals what structure is involved, so that treatment can be initiated.

For omental evisceration, the horse is restrained, and rectal palpation performed to ensure that only the omentum is involved. Prolapse of the omentum can usually be managed by sedation and emasculating the omentum as far proximal as possible. For more severe cases, the horse is placed under short-term general anesthesia, and the omentum and scrotum cleaned and sterilely prepared. The omentum is emasculated as proximal as possible, and the scrotum packed with gauze and closed. Systemic antibiotics and NSAIDs are administered, and the packing removed in 2 days. Barring complications, antibiotics are discontinued on day 3.

If the small intestine is eviscerated, a short-term general anesthetic is given. The intestine is copiously lavaged and examined for damage. Avulsion of the mesenteric vessels or intestinal compromise require resection. The scrotum should be sutured closed over the eviscerated bowel, and the horse referred to a surgical facility. If the intestine appears healthy, it is replaced in the abdomen, which often requires dilation of the internal inguinal ring. Care should be taken to replace the intestine within the peritoneal cavity through the inguinal canal, and not through a separate, iatrogenic opening. If the herniation cannot be reduced confidently, the scrotum should be packed, sutured closed, and the case referred.

If the herniation can be reduced, the inguinal canal and scrotum are packed with sterile gauze, taking care to prevent introducing gauze into the abdomen, and the scrotum is sutured closed. A short segment of gauze is left exposed. Alternatively, the external inguinal ring and vaginal tunic can be sutured closed primarily instead of packing. Systemic, broad-spectrum antibiotics and NSAIDs are administered, and the horse monitored closely for development of colic or ileus, which may indicate intestinal devitilization. Should that occur, the horse must be referred for abdominal exploratory surgery. If the horse progresses well, the packing can be removed in 48 hr, and antibiotics discontinued 24 hr after removal. It is advised to perform a rectal examination before removing the packing to ensure herniation has not recurred and the intestine has not adhered to the packing material.

Last full review/revision September 2014 by Amelia S. Munsterman, DVM, MS, DACVS, DACVECC

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