33rd Annual Scientific Meeting proceedings

Complications from surgical intervention to the upper airway can be rapid and fatal in dogs and cats. They include swelling from edema and inflammation, regurgitation hemorrhage, voice change, nasopharyngeal reflux, intranasal obstruction, epiglottic retroversion, laryngeal collapse, laryngeal webbing, aspiration pneumonia and pharyngeal collapse. Transient or permanent, unilateral or bilateral laryngeal paralysis can also occur following tracheal surgery and thyroidectomy, in both dogs and cats.

One of the best ways of dealing with upper airway complications is to anticipate them – always assume that the patient could develop complications and always have a plan to avoid or mitigate these occurrences in the post-operative period. If you are doing upper airway surgery regularly, you must have access to 24-hour, continuous, post-operative monitoring. Attentive post-operative monitoring is critical in upper airway patients - and in all brachycephalic patients regardless of the surgical intervention performed. Observe the animal closely until the animal is ambulatory – this means that someone should be physically present with the animal from the time of pre-medication until it is walking around in the post-operative period.

An accurate upper airway examination is important to ascertain the issues, their severity, what procedure(s) is indicated, and the likelihood of complications. Trying to examine the larynx and pharynx of the conscious animal is unrewarding – it needs to be done under a light plane of anesthesia, often with incremental small boluses if using propofol or alfaxalone. Following induction, sling the maxilla, have nothing touching the ventral neck area, pull the tongue a little rostrally, but not too much tension as it distorts the hyo-laryngeal anatomy. A Weider tongue blade can depress the tongue base effectively to improve visual access. Do most of the upper airway examination with cotton tipped applicators and small wooden tongue depressors. Take your time and be thorough, have an endotracheal tube close by. Most of the upper airway exam can be done with a laryngoscope, although small videoscopes have a better light source and the advantage of being able to assess trachea, mainstem bronchi and nasopharynx with retroflexed view, as well as recording the examination. All airway structures should be assessed for symmetry, function, mucosal condition, phlegm. Consider using a standardized upper airway examination sheet.

Additional imaging is extremely useful for assessing the upper airway. An extubated head and neck CT with hanging head gives an evaluation of the nasal turbinates, choanae, nasopharynx, palatal thickness and infraglottic lumen. Including thorax and abdomen in the scan can assess the trachea, bronchi and lungs and evidence of chronic gastroesophageal reflux or hiatal hernia.

It is important to realize that if we fail to recognize the full extent and severity of upper airway anomalies, then we will not address them completely and appropriately, and thus will be faced with complications. For example - dogs can have several (related or unrelated) conditions, such as tracheal collapse and pharyngeal collapse, pharyngeal collapse and epiglottic retroversion, or brachycephalic airway syndrome (BAS) and an intranasal epidermoid cyst. The other advantage of a thorough assessment is providing accurate prognosis for owners and managing their expectations.

Edema and Inflammation
The respiratory tract is extremely prone to edema when subjected to traumatic or surgical disruption.  Most surgical interventions within the upper airway should receive intravnenous dexamethasone 30 minutes before surgery (unless contraindicated due to concurrent NSAID administration or other issue), usually at 0.25 mg/kg. A smaller, lubricated ET tube (we always use guarded tubes) will be less traumatic to the laryngeal aditus, infraglottic lumen and trachea. Laryngotracheal swelling results in exponential resistance to airflow (Poiseuille’s Law) causing significant post-operative stridor and obstruction.

Following surgery to the larynx and pharynx, packing the pharynx completely with mannitol-soaked gauze for 45 minutes minimizes immediate post-operative swelling. If swelling becomes significant after 6 -12 hours, this can be repeated in an effort to avoid temporary tracheostomy tube placement.

If allowed to recover in a quiet environment without stimulation, the animal will generally tolerate the endotracheal tube until fairly conscious. Physical maintenance of an airway should extend until the dog will absolutely no longer tolerate an ET tube; by then it can then employ its pharyngeal musculature to keep the oropharynx open and be conscious enough to protect its airway from aspiration if it regurgitates. Recovery for 2 hours in a climate-controlled oxygen cage (40% oxygen) is routine at our institution.

If post-operative edema is causing respiratory embarrassment, racemic epinephrine can be nebulized, while animal is still being recovered and the maxilla is slung. Always be prepared to re-intubate, with intravenous anaesthetic agents drawn up and the IV catheter still in place. If still no improvement after 30 minutes, reintubate and repack the pharynx with mannitol-soaked sponges again. Call the owners to discuss temporary tracheostomy placement for 2-3 days. After placing the temp trach tube and the ET tube has been removed, examine the upper airway again before recovery to assess the degree of compromise. Swelling usually resolves within 24 - 48 hours, depending on the size of the airway. Occasionally, a temporary tracheostomy stays in for longer. Familiarize yourself with tracheostomy tube maintenance, as your team is now responsible for this animal’s airway.

Whenever you experience significant post-operative edema, review your surgical technique to determine if it could be modified. Atraumatic surgical technique will minimize post-operative edema – using sharp incisions (with scalpel or sharp scissors), gentle tissue handling (using stay sutures or atraumatic forceps for retraction), fine suture material with a swaged needle, CO₂ laser and needle-tip electrocautery have less collateral damage than vessel-sealing devides.

Regurgitation
It is always worth asking the owner if their dog has a history of regurgitation – consider a standardized upper airway history questionnaire. Bulldogs (and dogs with geriatric onset laryngeal paralysis polyneuropathy) are particularly prone to gastroesophageal reflux and regurgitation, and we routinely prescribe anti-reflux and prokinetic medications to be started a week or so prior surgery. These medications can be extended into the post-operative period for several weeks, especially if the soft palate has undergone surgery, as stimulation of the soft palate and pharyngeal roof can result in a tendency to gag. Avoid drugs that can lead to regurgitation or vomiting, such as hydromorphone, especially in the pre-operative period. After surgery but before pharyngeal packing, suctioning the pharynx and esophagus with a whistle-tip catheter can sometimes yield a significant amount of fluid, and is recommended.

Hemorrhage
Hemorrhage is a rare complication of upper airway surgery but can be serious due to direct aspiration, or swallowing, regurgitation then aspiration of blood. The most common sites of hemorrhage are the tonsillar crypts, the thick soft palate, and the vocal folds. With this awareness and the availability of modern hemostatic devices, attention to technique will eliminate this complication. The use of tonsillar balls (or gauze) to pack the pharynx during surgery and ensuring that the ET tube cuff is adequately inflated will prevent tracheal aspiration or swallowing of any blood. The meticulous use of needle-tip electrocautery along with gentle suctioning will facilitate hemostasis also protect intraoperative aspiration of blood. Secure suturing of thick palates will also minimize hemorrhage. Any significant bleeding from the oral cavity or vomiting of blood in the immediate post-operative period is an indication for immediate re-exploration of the operative site, and attenuation of the vessels.

Voice change
A changed (hoarse) bark is an indication that the vocal folds have likely been damaged, and this occurs during ventriculectomy (sacculectomy). It reflects poor technique, so worth learning from this if it happens. The use of fine-tipped Reynolds scissors, or Sweet pituitary scissors makes accurate resection of ventricular tissues much easier, and can be done with ET tube in place. If the vocal cord has been damaged, the animal is placed on a 3-week taper of prednisone. If both vocal cords have been damaged, the risk of cicatrix (scarring) formation is higher, and a ventral web of tissue may cause permanent obstruction. If this occurs, a ventral laryngotomy and resection of scar tissue and obtaining good mucosal apposition is indicated. There is also a voice change and some stridor when one of the recurrent laryngeal nerves has been damaged, but will typically not cause respiratory distress and will resolve in time unless the nerve has been transected or severely retracted causing a permanent neuropraxia.

Other complications that can be sometimes avoided and will be discussed pending time include:

• Nasopharyngeal reflux & dysphagia
• Intranasal obstruction – failure to recognize
• Epiglottic retroversion
• Pharyngeal collapse