Manual of Equine Anesthesia and Analgesia. Группа авторов

and smaller horses to prevent extreme arterial hypertension.

      E Obstruction of the nasal passages due to nasal bleeding

       Bleeding upon removal of a nasotracheal or nasogastric tube can be quite alarming.

       The author's preference is to remove nasogastric tubes approximately 30 minutes before the end of anesthesia, as this will allow time for bleeding to stop prior to the horse being placed in recovery.

       If bleeding is anticipated, or happening while the horse is still tracheally intubated in recovery, the ET tube should be left in place until the bleeding has ceased or perhaps until the horse is standing.

       If the horse has been extubated, it may be necessary to pass a nasotracheal tube down the unaffected nostril to establish an airway.This can be difficult unless the horse is in a relatively deep plane of anesthesia.

       Some cases necessitate deepening anesthesia to facilitate re‐intubation of the trachea and to prevent the horse awakening until the hemorrhage has ceased.

       If the horse is laterally recumbent, the head must be tilted downward to prevent aspiration of blood.

Suggested Reading

      1 Lukasik, V.M., Gleed, R.D., Scarlett, J.M. et al. (1997). Intranasal phenylephrine reduces post anesthetic upper airway obstruction in horses. Equine. Vet. J. 29: 236–238.

      2 Richardson, E. and McMillan, M. (2017). A case of airway obstruction caused by probable nasotracheal tube cuff herniation in a horse. Vet. Anaesth. Analg. 44: 191–192.

      3 Touzot‐Jourde, G., Stedman, N.L., and Trim, C.M. (2005). The effects of two endotracheal tube cuff inflation pressures on liquid aspiration and tracheal wall damage in horses. Vet. Anaesth. Analg. 32: 23–29.

Tracheostomy

       Tanner Snowden and Jim Schumacher

      I Terminology

       A tracheostomy is a surgically‐created opening into the trachea. The terms tracheostomy and tracheotomy are used interchangeably.

       Temporary tracheostomy

       This is performed to temporarily bypass an obstruction of the respiratory tract proximal to the site of tracheostomy.

       The tracheostomy tube is removed when the obstruction has resolved, allowing the tracheostomy to heal.

       A temporary tracheostomy may be an emergency procedure when the obstruction is life‐threatening.

Permanent tracheostomy (see Figure 4.11)

       This is performed to create a permanent tracheal fistula, or stoma. A tracheal stoma can be created when the obstruction to airflow is severe and permanent.

       Creating a tracheal stoma involves removing a portion of four or five adjacent tracheal rings and suturing the tracheal mucosa and submucosa to the surrounding cutaneous incision.

       The term permanent tracheostomy is sometimes used to describe a stoma that is maintained only during a working season for the horse. This is similar to a temporary tracheostomy but is performed because the obstruction to airflow interferes only with the work of the horse. Though termed a “permanent” tracheostomy, this tracheostomy is not actually permanent, because the tracheostomy tube is removed after the working season of the horse, when it is no longer required. The tube is replaced, in preparation for the horse's next working season, after performing another tracheostomy.

Figure 4.11 Permanent tracheostomy performed to bypass laryngeal obstruction causing severe dyspnea.

      Source: Courtesy of: Dr. Peter Rakestraw, VMD, Dip ACVS.

      II Indications

       To bypass an obstruction of airflow proximal to the site of tracheostomy. The horse is an obligate nasal breather, so severe obstruction of the nasal cavity necessitates creating a tracheostomy.

       To provide access to the trachea for administering an inhalant anesthetic and oxygen, so that surgery of the larynx or pharynx (e.g. resection of the nasal septum, arytenoidectomy, repair of a cleft palate) can proceed unimpeded by the presence of an ET tube.

      III Surgical anatomy

       Structures overlying the site of tracheostomy include the skin and cutaneous coli, sternohyoideus, and thyrohyoideus muscles.

       The site of tracheal incision is the annular ligament of the trachea, which attaches one tracheal ring to another.

IV Tracheostomy tubes (see Figure 4.12)

       J‐type tube.

       Dyson tube (self‐retaining).

       Bivona silicone tube.

       A temporary tracheostomy tube can be made, in an emergency, from the handle of a one‐gallon plastic jug or the cut end of a large stomach tube or garden hose.

Figure 4.12 Tracheostomy tubes: Bivona silicon tube (a), Dyson tube (b), a tube made from a gallon plastic jug (c), and a J‐type tube (d).

      V Technique

       Tracheostomy is usually performed with the horse standing, but can also be performed under general anesthesia in anticipation of a post‐surgical obstruction.

       The procedure is performed most easily with the horse restrained in stocks and sedated with an alpha2 agonist, such as detomidine HCl (0.005–0.01 mg/kg, IV) or xylazine HCl (0.2–0.5 mg/kg, IV)Butorphanol tartrate (0.02–0.03 mg/kg, IV) can be administered after the horse is sedated, if necessary, to provide more profound sedation.

       The usual site is the juncture of the cranial and middle third of the cervical portion of the trachea (3rd to 6th tracheal rings).The trachea can usually be palpated easily at this site.If the surgeon anticipates that the horse may later require a permanent tracheostomy, the site of temporary tracheostomy should be far enough distal on the neck that it does not interfere with creating a permanent tracheostomy.

       Hair at the proposed site of incision is clipped, and the site is scrubbed.

       8–12 ml of local anesthetic solution is injected subcutaneously at the proposed site of incision (see Figure 4.13).

       A