Manual of Equine Anesthesia and Analgesia. Группа авторов

is made through the skin, subcutaneous tissue, and cutaneous coli muscle (see Figure 4.14).

       The juncture between the right and left sternohyoideus muscles and the right and left sternothyroideus is incised with a scalpel or scissors. Finding the site of the juncture is often difficult and not absolutely necessary.Avoid inadvertently scoring the tracheal rings when the musculature is incised with a scalpel.

       Retracting the skin and musculature with a Weitlaner or Gelpi retractor helps to expose the trachea (see Figure 4.15).Inserting a retractor into the wound can be omitted if the tracheostomy is being performed with urgency.Figure 4.13 Local anesthetic is instilled subcutaneously at the proposed site of incision in preparation for performing a temporary tracheostomy.Figure 4.14 A cutaneous incision is created on the ventral midline of the neck over the palpable trachea. This incision is extended through the cutaneous colli and the right and left sternothyroideus muscles to expose the tracheal rings.Figure 4.15 The trachea can be better exposed by separating the cutaneous and muscular incision with a self‐retaining retractor.

        The annular ligament between two tracheal rings is identified in the center of the incision, and this ligament is incised with a scalpel blade to expose the lumen of the trachea, being careful to avoid inadvertently incising the mucosa on the dorsal side of the trachea.The ligament and underlying tracheal mucosa are incised to the right or left, and without removing the blade from the incision, the blade is turned over, and the incision is lengthened in the other direction.Ideally, the tracheal incision should be approximately one‐third of the circumference of the trachea if a tracheostomy tube is to be inserted. The incision needs to be larger, if it is created for insertion of an endotracheal tube through which an inhalant anesthetic and oxygen are to be administered.The tracheal incision should not exceed half of the tracheal circumference.Extending the incision beyond one‐half of the circumference risks formation of a restrictive cicatrix and transection of an adjacent carotid artery or a nerve, such as the vagosympathetic trunk or recurrent laryngeal nerve, which lies adjacent to the carotid artery.Note: The scalpel blade should be attached to a scalpel handle, if time allows, so that inadvertent loss of the blade into the lumen of the trachea is avoided.Incision into the tracheal lumen can be recognized by escape of air through the wound when the horse exhales. The horse may cough, because of blood entering the tracheal lumen.

       A finger or the jaws of a large forceps are inserted into the lumen of the trachea, through the incised annular ligament and tracheal mucosa, and the cannula of a tracheostomy tube is inserted between the two separated tracheal rings, adjacent to the finger or jaws of the opened forceps, into the lumen of the trachea.

       The tracheostomy tube is secured to the site of tracheostomy. Each side of the faceplate (or neck flange) of a J‐tube has a slot through which rolled gauze can be threaded and tied around the neck.To ensure that a J‐tube does not become dislodged, it can be sutured to the neck through the slot on each side of the faceplate or secured to the neck with elastic adhesive tape.Dyson tubes are self‐retaining and need not be secured.

       To ease replacing the tube, a long suture can be placed around each ring adjacent to the tracheal incision. Traction on these sutures widens the tracheal incision for easy insertion of the cannula of the tube and prevents the cannula of the tube from being inserted subcutaneously.The cannula is easily replaced, without the use of sutures, after the wound has developed granulation tissue, usually by day 6.

       Some clinicians, when anticipating a lengthy period of tracheal cannulation, such as for maintaining a tracheal stoma for a working season, remove a crescent‐shaped section of cartilage from the distal aspect of the ring proximal to the incision in the annular ligament, and a similar section from the proximal aspect of the ring distal to the incision in the annular ligament (see Figure 4.16).Although removing sections of cartilage may ease daily insertion of the tracheostomy tube, removing cartilage is seldom necessary.

      VI Post‐operative care

       The horse should be administered a tetanus toxoid vaccination, if it has not received one within the previous year.It should be administered a tetanus toxoid vaccination and tetanus antitoxin if it has never been vaccinated against tetanus.

       The horse should be administered a broad‐spectrum antibiotic until the tracheal wound begins to develop granulation tissue, usually at five to six days.

       Compressing the tissue at the site of tracheostomy by securing the tracheostomy tube with an elastic adhesive bandage applied around the neck and faceplate, leaving the entrance to the cannula uncovered, may decrease the severity of subcutaneous emphysema, which frequently develops at the site.Figure 4.16 To ease daily insertion of a tracheostomy tube, a crescent‐shaped section of cartilage can be excised from the distal aspect of the ring proximal to the incision through the annular ligament of the trachea, and a similarly shaped section of cartilage can be removed from the proximal aspect of the adjacent ring.Source: Courtesy of Dr. Peter Rakestraw, VMD, Dip ACVS.Figure 4.17 Compressing the faceplate of the tracheostomy tube against the tracheal incision diminishes the likelihood of the horse developing excessive subcutaneous emphysema adjacent to the incision.

       The tracheostomy tube should be cleaned or replaced with a clean tracheostomy tube, preferably twice daily. More frequent cleaning or replacement may be necessary if the cannula accumulates exudate rapidly.A clean tube should be inserted as soon as the soiled tube is removed, if the horse is totally dependent on the tracheostomy to breath.

       The necessity for maintaining a tracheostomy tube can be evaluated by sealing the opening of the tube with tape and evaluating how the horse breaths. Note: Even if the airway proximal to the tube is no longer obstructed, the horse may have difficulty breathing when the opening is sealed, if the tube is so large that an adequate volume of air cannot move around it. This is more likely to happen if the patient is a foal or a miniature horse.

       The wound heals rapidly by second intention after the tube is removed.A tracheostomy that has developed granulation tissue is likely to be healed between two and three weeks after the tube is removed.A thin epithelial scar is often present at the healed site of the temporary tracheostomy.

       The wound should be cleaned of exudate once or twice daily. Petroleum jelly should be applied to the skin around the wound, after the wound has been cleaned, to make subsequent cleaning easier.Avoid using soap on the wound.Avoid introducing fluid into the tracheal lumen while cleaning the wound.

      VII Complications

       When a tracheostomy is performed with the horse anesthetized, the cutaneous and tracheal incisions are sometimes found to be mismatched when the horse stands, because when the horse is recumbent and in dorsal recumbency, with its neck extended, the trachea shifts in relation to the overlying skin.

       Incising the annular ligament more than 180° of the circumference of the trachea may result in an obstructing cicatrix when the tracheal incision heals, and the procedure risks transection of a carotid artery or adjacent nerve, such as the vagosympathetic nerve, which lies dorsal to the carotid artery, or the recurrent laryngeal nerve, which lies ventral to the carotid artery.

       The site of tracheostomy may develop a stricturing cicatrix if the mucosa on the dorsum of the trachea is incised inadvertently when the tracheostomy is created.This complication is most likely to occur when tracheostomy is performed on a small equid.A tracheostomy tube can be accidentally inserted into the inadvertently‐created