Diseases of the upper airway such as laryngeal hemiplegia, arytenoid chondritis, subepiglottic cysts, aryepiglottic fold entrapment, and dorsal displacement of the soft palate are commonly encountered in horses. In all of these conditions some abnormality of the upper airway compromises the cross-sectional area of the airway and causes decreased airflow; the condition usually becomes clinically significant only at exercise. In the majority of these cases, surgical correction specifically addresses the area of compromise and corrects the abnormality.
Certain conditions exist, however, in which the lesion causes such severe stenosis of the upper airway that surgical correction of the lesion is met with a guarded or poor long-term prognosis. In this author’s experience and based on literature review, the most common conditions in which less invasive procedures have failed are related to the problem of nasopharyngeal cicatrix. In this syndrome, a circular web of tissue forms in the pharynx, first ventrally over the floor of the pharynx and then dorsally, in which position it extends above the pharyngeal openings of the guttural pouches. Arytenoid chondritis is commonly associated with this generalized inflammatory process. Resection of the diseased cartilage does not seem to be curative because the generalized inflammatory process continues with the subsequent pharyngeal/laryngeal swelling that leads to obstruction of the airway. In these cases, permanent tracheostomy can provide an effective alternative approach by bypassing the obstruction. Other indications for a permanent tracheostomy are neoplasia of the upper airway and severe deformity of the nasal passages.
Although permanent tracheostomy can be performed with the horse under general anesthesia, the technique described here can be readily performed in the standing horse. This provides some advantages because the surgical structures are in a more normal anatomic orientation and create less tension on the tracheostomy closure during the healing period. This position also avoids complications associated with general anesthesia and recovery and reduces the expense of the procedure.
Perioperative antibiotics (procaine penicillin G, 20,000 IU/kg q12h, IM) and antiinflammatories (flunixin meglumine, 1.1 mg/kg IV) should be administered. The horse is restrained in the stocks and cross-tied so that it is positioned forward in the stocks with its head extended in front of the side poles of the stocks. With this restraint, the surgeon has easy access to the surgical area. Maintenance of this position is easier if the horse’s head is suspended from a bar that extends from the top of the stocks over the head. The head is suspended by means of the halter that is placed upside down so that the throat-latch strap is over the horse’s forehead (between the eyes and ears) and not under the throat adjacent to the surgical site. Padding should be placed between the halter and the mandible to prevent facial nerve paralysis. Placement of the horse’s head in a stand similar to a crutch may also help in maintaining the head and neck in an extended position. Sedation and analgesia is provided by administration of detomidine (0.02 mg/kg, half administered IV and half IM) and butorphanol (0.011 to 0.022 mg/kg IV).
The incision is positioned over the second to sixth tracheal rings. Local anesthesia is infiltrated subcutaneously in an inverted U pattern dorsal and lateral to the second through sixth tracheal rings. Starting approximately 3 cm distal to the cricoid cartilage and centered over midline, the surgeon removes a 3-cm wide x 6-cm long rectangular section of skin. The surgeon then continues the incision on midline, separating the paired sternothyrohyoideus muscles to expose the tracheal rings. Dissection is performed laterally around the abaxial borders of the paired sternothyrohyoideus muscle. The muscle bellies are isolated and clamped (Ferguson Angiotribe Forceps; Miltex, Lake Success, N.Y.) at their proximal and distal exposure in the incision. After clamping for several minutes to crush the vessels, the muscle bellies are transected. This author also recommends removal of a section of the omohyoid muscle in a similar fashion. The fascia covering the tracheal rings is carefully removed. A ventral midline incision and two paramedian incisions, approximately 15 mm on either side of the midline incision, are made through the tracheal ring cartilage without penetrating the tracheal mucosa. The tracheal cartilage segments are carefully dissected free from the tracheal submucosa, leaving the submucosa and mucosa intact. Although this may appear very difficult, the mucosa is thick and separates easily from the rings with patient dissection.
Most commonly a total of five tracheal rings (two through six) are removed although removal of four rings is often adequate. To alleviate dead space, subcutaneous tissue is sutured to the tracheal fascia with 0-polydioxane (PDS; Ethicon Inc, Somerville, NJ.) with use of a simple interrupted pattern. In some horses this author inserts a 23-gauge, 2.5-cm needle into the lumen of the trachea and injects 30 ml of 25% lidocaine HCl proximal to the incision to desensitize the tracheal mucosa. The tracheal mucosa is incised in what has been described as a double Y pattern. In this pattern, a central midline incision is made that ends approximately one tracheal ring width before the rostral and caudal ends of exposed tracheal mucosa. The midline incision is extended as a V with each leg connecting to the corners of one end of the exposed rectangular section of tracheal mucosa. In this way, a double Y pattern is formed. The surgeon sutures the tracheal mucosa and submucosa to the skin with simple interrupted sutures of 0-polydioxone, starting at the ends and then suturing along the lateral borders.
Permanent Tracheostomy in Standing Horses: Aftercare
Because the proximal trachea is not a sterile environment, antibiotics should be administered for 5 to 7 days postoperatively. Nonsteroidal antiinflammatory drugs should be continued for 5 to 7 days depending on the amount of postoperative swelling. The stoma should be cleaned once or twice daily until the sutures are removed 10 to 14 days after surgery. The stoma needs to be cleaned daily for the first month after surgery, but usually by 1 to 2 months postoperatively the discharge will decrease and make daily cleaning unnecessary. In the majority of this author’s long-term postoperative cases, cleaning has been necessary only once or twice a week.
In this author’s experience, postoperative swelling with or without partial dehiscence is the most commonly encountered complication. Incisions that develop partial dehiscence can heal satisfactorily by second intention. In some cases the areas of partial dehiscence have had to be surgically repaired, a method that usually involves removing more of the adjacent muscle and resuturing the mucosa and submucosa to the skin. In a small percentage of cases that had insufficient stoma size repairs were made by removing sections of the omohyoid muscle. Because of this experience, this author now routinely removes a portion of the omohyoid when performing a tracheostomy.
Permanent Tracheostomy in Standing Horses: Prognosis
In this author’s experience the long-term prognosis after tracheostomy is good, and more than 90% of owners say that they are pleased with the outcome. Tracheostomy has been performed on many broodmares without causing problems during foaling, although close observation of the mare around the foaling period is still recommended. In some horses the tracheostomies were performed more than 10 years ago and the stoma is still patent and causes no problems. This procedure does not prevent the horse from being used for athletic purposes; some of the aforementioned horses are used for pleasure riding and some used as Western performance horses. Although the tracheostomy bypasses a component of the pulmonary defense mechanism that acts to moderate temperature and humidity and filter inspired air, these horses have not appeared to be predisposed to airway infections. Approximately one fourth cough occasionally during exercise, most likely because of irritation of the trachea from dust particles. Consequently maintenance of the horses in an environment that is as dust-free as possible is recommended.