Etiology

Primary choke is most often caused by impaction with common feeds that are of poor quality, are eaten excessively fast, or are poorly masticated because of bad teeth or oral ulcers (such as might develop secondary to equine herpesvirus 2 infection). In addition, ingestion of foreign bodies, carrots, apples, corncobs, shavings, or medicinal boluses can lead to esophageal obstruction. Other predisposing factors are eating too early after sedation or general anesthesia, consumption of pelleted or cubed feed, and inadequate water intake. Secondary esophageal obstructions are caused by anatomic abnormalities that mechanically impede feed passage. Intraluminal obstructions might be caused by esophageal strictures, diverticula, inflammation, ulcerated mucosa (from a previous obstruction), congenital disorders (megaesophagus, stenosis, cysts, and vascular ring abnormalities), and neoplasia. Extraluminal causes include mediastinal or cervical masses, such as tumors or abscesses. In a study of 61 horses with esophageal obstruction, feed material was the cause in 27 horses, stricture in 18, esophageal perforation in 11, and diverticulum in 5. In another study, feed impaction caused the obstruction in 28 of 34 horses.

Esophageal obstruction may arise at any age; however, older horses and foals are more vulnerable because of poor dentition and predisposition to ingest foreign materials, respectively. Sequelae of esophageal obstruction include esophageal ulcer formation, rupture, and stricture, all of which lead to recurrent episodes of choke.

Clinical Signs

Clinical signs of esophageal obstruction include nasal discharge of feed material and saliva, hypersalivation, coughing, and frequent attempts to swallow. In a study of 34 horses with esophageal obstruction, nasal discharge containing ingesta and saliva was observed in 74%, coughing in 50%, gulping in 44%, and hypersalivation in 41%. Other less frequently seen signs include extension of the neck, abnormal lip movements, sweating, restlessness, and apathy. In some cases, distension of the cervical portion of the esophagus may be evident at the site of the obstruction. Complications associated with prolonged obstruction include dehydration, electrolyte disturbances, weight loss, aspiration pneumonia, and esophageal rupture.

Diagnosis

Because esophageal obstruction can be considered an emergency, diagnosis is initially made on the basis of clinical signs of nasal discharge containing feed material and saliva, hypersalivation, coughing, and palpation of the larynx and pharynx. Palpation of the left cervical area may reveal a mass associated with the impaction. The veterinarian’s inability to pass a nasogastric tube or endoscope is consistent with a complete obstruction. Careful passage of a nasogastric tube is a valuable method of confirming the location of an obstruction but provides little information about its nature or the condition of the esophagus. Endoscopic examination can help in determination of the nature and material of the obstruction, but depending on the material, the endoscope is usually not a good instrument to use in resolving the obstruction. Ultrasonography may reveal the location and extent of the impaction and the integrity of the esophageal wall. It may also help define any extraluminal masses and cellulitis in case of rupture. However, these ancillary diagnostic methods are frequently undertaken after the obstruction is resolved.

Radiographs of the cervical portion of the esophagus are easily taken with portable equipment and can reveal gas accumulation proximal to the retained fluid and food. For the best assessment of the obstruction, sedation and manipulations of the esophagus should be avoided before radiographs are taken. Double-contrast studies, obtained by insufflating air after barium has been administered, are useful for revealing strictures, diverticula, rupture, or masses. Barium can be given either in a food bolus to evaluate peristalsis or through a nasoesophageal tube to outline the esophagus and any possible anatomic defects.

To definitively determine the nature and extent of the obstruction, endoscopic examination is often required. An endoscope of 1.6 to 3.0 meters’ length may be necessary to reach the thoracic inlet and terminal segment of the esophagus. Transendoscopic forceps may be used to remove feed and foreign bodies and resolve the obstruction, but given the small cup size of most biopsy instruments, this can be time consuming and unrewarding. If a motility disorder is suspected and peristaltic movements need to be assessed, endoscopy should be performed without sedation, if possible. Esophagoscopy after removal of the obstruction best predicts the prognosis because it can reveal the cause of the impaction (e.g., whether caused by a diverticulum or a mass) and complications of the esophageal insult, such as ulceration or rupture.

After the obstruction is resolved, auscultation and ultrasonographic examination of the thorax are important to assess for secondary pneumonia and pleural fluid accumulation. Radiographic identification of an alveolar pattern in the cranioventral lung regions suggests aspiration pneumonia, which can develop acutely, within a few days of the initial episode, or can be chronic when choke is recurrent, especially in cases of esophageal stricture and diverticula. If aspiration pneumonia is suspected, a complete blood count (CBC) and plasma fibrinogen measurement can be used to assess the severity of inflammation. Bacterial culture and determination of antimicrobial sensitivity can be performed, but usually multiple species of bacteria are involved.

Management

Most horses can tolerate obstruction for 24 hours or more without significant esophageal damage. Nevertheless, the potential for dehydration and electrolyte disturbances, aspiration pneumonia, and esophageal ulceration make emergency treatment essential.

Treatment of choke initially consists of sedating the horse and providing supportive care because, in many cases, the obstruction will resolve spontaneously if the horse is rehydrated by intravenous fluid administration and the esophageal muscles are relaxed. Sedation with xylazine (0.25 to 0.5 mg/kg, IV) or detomidine (0.01 to 0.02 mg/kg, IV), in combination with acepromazine, (0.05 mg/kg, IV) or butorphanol (0.01 to 0.02 mg/kg, IV), will cause relaxation of the esophageal muscles and promote a lower head carriage, which assists drainage of feed and saliva from the nostril and prevents aspiration of feed material into the trachea. Oxytocin (0.11 to 0.22 IU/kg, IV) can be given for obstructions in the cervical portion of the esophagus to relax striated esophageal muscles.

If sedation alone does not result in clearance of the obstruction, the mainstay for the treatment of feed impactions remains the gentle introduction of a nasogastric tube. Esophageal irrigation with lidocaine (30 to 100 mL of 2% solution) provides local anesthesia of the esophageal mucosa and reduces esophageal spasm. The horse should be kept sedated with the head lowered during irrigation. Slow and gentle irrigation with warm water will soften most feed impactions and allow feed and water to drain around the tube and exit through the mouth and nostrils. The nasogastric tube should be gently advanced as the obstruction clears.

If gentle lavage does not relieve the obstruction, the horse can be stalled and sedated and rehydrated with intravenous fluids for several hours before another attempt is made. If continued attempts are unsuccessful, more vigorous lavage can be done, with the horse either under general anesthesia or standing and sedated. In both situations, the airway must be protected by placing a cuffed nasotracheal tube in the trachea or a cuffed large tube in the esophagus with a smaller inner tube used to irrigate the obstruction. General anesthesia with tracheal intubation provides excellent protection of the airway and optimal relaxation of the esophageal musculature. The horse should be positioned with the head in a dependent position to promote drainage. To prevent aspiration, a cuffed endotracheal tube should be left in place while the horse recovers from anesthesia. Lavaging the esophagus with fluids containing mineral oil or dioctyl sodium succinate must be undertaken with caution because aspiration of these substances will complicate pneumonia. Surgical relief of the obstruction through esophagotomy is rarely indicated and should be reserved for cases in which repeated medical treatment fails to resolve the obstruction.

Aspiration pneumonia should always be considered a complication of esophageal obstruction, and broad-spectrum antimicrobials should be administered, especially when the condition lasts for more than 12 hours. Flunixin meglumine (1.1 mg/kg, PO or IV, every 12 hours) or phenylbutazone (4.0 mg/kg, PO or IV, every 12 hours) should be administered to reduce pain and inflammation, which can lead to stricture formation.

Follow-Up Evaluation and Diet Reintroduction

In the first 24 hours after resolution, an endoscope should be passed to determine the severity and extent of esophageal damage. If there is minimal or no damage to the esophagus, the horse should be allowed access to water. In horses with a simple obstruction and when minimal to no esophageal damage is present, feed (mash made of soaked pellets) or grass can then be slowly reintroduced. In more complex cases, in which the esophageal mucosa has become ulcerated, the horse should be held off feed for 48 hours and then cautiously reintroduced to feed and water. Easily digested pelleted feeds can be made into a mash or gruel with water. The horse can be grazed on grass for 15 minutes every few hours. Soft feeds minimize trauma to the esophagus and are easily swallowed by the horse if the esophagus is painful. Postobstructive esophagoscopy can help direct the feeding regimen by revealing the extent of damage. Hay and large-stem feedstuffs should be reintroduced slowly over the course of several days to weeks, depending on esophageal damage. Small, frequent feedings minimize esophageal irritation and scar formation and help prevent stricture formation. Administration of sucralfate (22 mg/kg, PO, every 6 to 8 hours) can be helpful in coating esophageal ulcers and facilitating healing.

Complications and Prognosis

Complications are common after esophageal obstruction, with a 51% complication rate reported in a recent study. The most common were aspiration pneumonia, esophageal stenosis, stricture formation, fever, and diverticula. Esophageal perforation, cellulitis, mediastinitis, pleuritis, left laryngeal hemiplegia, and laminitis were less common. Factors associated with development of complications included being a stallion, age greater than 15 years, undergoing general anesthesia, radiographic signs of aspiration pneumonia, total plasma protein higher than 7 mg/dL, severe esophageal lesion, and duration of esophageal obstruction longer than 48 hours. Respiratory rate higher than 22 breaths/minute and moderate or severe tracheal contamination significantly increased the risk for aspiration pneumonia.

Endoscopic reevaluation should be performed with 24 hours of relief of the obstruction and then every 2 to 4 weeks if esophageal dilation or mucosal injury is observed. If the mucosal integrity is maintained but the mucosa is discolored or bruised, a follow-up endoscopic examination should be performed within a week of the initial exam. Additional radiographic evaluation may be warranted to assess motility and transit times.