Manual of Equine Anesthesia and Analgesia. Группа авторов

the trachea using the stomach tube as a guide, and the stomach tube is then removed.The stomach tube should be of sufficient diameter and wall thickness that it will not kink as the ET tube is advanced as this will entrap the ET tube and hinder its PASSAGE.

      VI Extubation of the trachea

       Spontaneous breathing should have resumed before the tube is removed in recovery.

       Confirm that the horse is taking regular deep breaths.

       Removal of the tube before the horse has regained the swallowing reflex is generally acceptable, but many advocate waiting until this reflex has returned.

       It is also acceptable to leave an orotracheal or nasotracheal tube in place during recovery and this may be indicated under certain circumstances (see Figure 4.9).This is generally indicated if there is a risk of regurgitation of gastric contents as in some colic cases.Figure 4.9 Horses with orotracheal (a) and nasotracheal (b) tube in recovery. Ideally, the tube should not protrude beyond the lips as this could lead to kinking of the tube if it were to impact the wall of the recovery box.In these cases, it is also prudent to tilt the head downwards in recovery to facilitate pharyngeal drainage.However, if left in place, the tube should not protrude much distance from the mouth to avoid it kinking in the event that it gets impacted against a wall of the recovery stall.

       Horses tolerate orotracheal and nasotracheal tubes well during recovery.

       Since the horse does not produce significant salivary secretions, it is not necessary to drain or suction the oropharynx prior to tube removal. The exception is in cases of reflux of gastric contents into the oropharynx.

      VII Airway obstruction

       The importance of preventing airway obstruction cannot be over emphasized.

       Obstruction in the recovery phase will lead to extreme anxiety in the awakening horse such that it may be impossible to control the horse to establish an airway.

       In extreme cases, airway obstruction may result in negative pressure pulmonary edema (NPPE) which can be fatal (see Chapter 38).

       Thus, it is important to have a plan to protect the airway, and to check for airway patency following ET tube removal.

       Because airway obstruction is most likely to result from nasal edema, administration of phenylephrine intranasally or placement of a nasal tube will greatly reduce the incidence of airway obstruction (see Figure 4.10).Airway obstruction, due to nasal edema is more likely to occur when the horse has been in dorsal recumbency for long periods.

Figure 4.10 Phenylephrine used to resolve nasal edema prior to recovery.

A Signs of airway obstruction include:

       Snoring sounds.

       No evidence of air passage via nostrils or decreased air passage.

       Increased abdominal effort on inspiration and expiration.

       Abnormal abdominal movements (e.g. retraction of abdomen on inspiration).

       Nostril flaring on inspiration.

      B Laryngospasm

       Defined as reflex closure of the vocal cords.

       Is uncommon in the horse.

       Indeed, the larynx of the horse is much less sensitive than in other species.

      C Obstruction of the upper airway

       At induction

       Obstruction is a rare occurrence at induction, unless there is a space‐occupying mass in the pharynx or nasal passages, or the horse has severe recurrent laryngeal neuropathy.

       However, as previously mentioned, overzealous attempts to intubate may cause a partial obstruction either by causing edema or by displacing the epiglottis.

       Management

       If obstruction is anticipated, a plan should be in place to secure the airway. This may involve performing a tracheostomy or having an endoscope available.

       In some cases of partial obstruction, passing a stomach tube of suitable size into the airway (see Sections V–E) to serve as a guide over which the ET tube can be passed, is usually successful.

       Intraoperative obstruction

       Obstruction is an uncommon occurrence in the intubated horse.

       However, extreme flexion of the neck may result in kinking and obstruction of the endotracheal tube.The most likely scenario for this occurrence is during radiographic imaging of the cervical vertebrae, during which extreme flexion of the neck is employed.

       At extubation

       The horse must suddenly change from being a mouth breather to having to resume nasal breathing, so obstruction of the upper airway is more likely to occur following extubation, especially if the horse is still deeply anesthetized.

       Airway patency should be checked after extubation by placing a hand close to the horse's nostrils and checking for airflow, while at the same time observing thoraco‐abdominal excursion. The thoraco‐abdominal movements should be smooth, and not accompanied by inspiratory or expiratory effort or upper airway noises indicative of obstruction.

       The epiglottis needs to be re‐aligned to its normal position, dorsal to the soft palate, for successful nasal breathing to resume.

       Management

       The condition may resolve by flexing and extending the next a few times. Otherwise, gentle passage of a small‐bore nasal tube into the larynx may re‐align the epiglottis.

D Obstruction of the nasal passages due to edema

       Is a common occurrence, especially following a prolonged period of anesthesia with the horse in dorsal recumbency.

       Edema develops because of the increased hydrostatic pressure in the nasal mucosa in dorsal recumbency.

       Passage of a nasal or nasotracheal tube is usually effective in the treatment of nasal obstruction.A 14–16 mm tube will suffice for an adult, and should be left in place for recovery.Routine use of a nasal tube or orotracheal tube in recovery is recommended following long surgeries, especially if the horse has been in dorsal recumbency.

       Phenylephrine instillation, to constrict nasal mucosa, can be used to reduce edema.Phenylephrine can be squirted into the nasal passages via the ventral meatus by elevating the nose and allowing contact with the nasal mucosa.5 ml of 0.15% phenylephrine (adult, full‐sized horse) into each nostril, about 30 minutes before extubation, will