Approach to the Upper Airway in the Field

Approach to the upper airway in the field Sophie H. Bogers, BVSc, MVSc, PhD, DACVS-LA Session Description: This session will provide a general overview of approaches to the diagnosis of upper airway conditions. The use of endoscopy, radiography and ultrasound to distinguish between commonly confused conditions will be discussed. The indications and techniques for field upper airway surgery including tracheostomy and sinus trephination will be discussed. Speaker Notes: 1. The diagnostic approach to the upper airway case often follows a similar pattern. The results of the history, physical examination and resting endoscopy will allow you to focus more on techniques specific to the sinus or nasal passages or the larynx and pharynx 2. Endoscopy helps you to pin-point what structures in the upper airway are affected. There are exceptions if you don’t have an endoscope e.g. for suspected dental sinusitis that causes foul smelling nasal discharge an oral examination can be done first and if no obvious occlusal abnormalities are seen then endoscopy can be performed after to confirm that the drainage is coming from the paranasal sinuses. a. The endoscopic examination should be thorough with assessment of all of the structures below: i. Larynx (make swallow several times – see EE/subepiglottic cyst/abduction of arytenoid maximal) 1. Assessment of larynx when not sedated (may sedate for remainder) ii. Trachea iii. Dorsal pharyngeal recess and pharynx iv. Guttural pouch 1 v. Ethmoid turbinates vi. Sinus drainage angle vii. Nasal passage 1 – nasal septum, ventral conchal bulla viii. Change sides 1. Guttural pouch 2 2. Nasal passage 2 b. Following the same steps every time for upper airway endoscopy will allow you to detect subtle abnormalities 3. If you detect an abnormality with the larynx or pharyx: a. Some conditions seen at rest easily – left laryngeal hemiplegia, arytenoid chondritis, persistent dorsal displacement of the soft palate b. Other conditions of the pharynx and larynx only occur during exercise – dorsal displacement of the soft palate, aryepiglottic fold collapse, vocal fold collapse, rostral displacement of the soft palate (or any other soft-tissue structures that can be pulled into the airway lumen by the negative pressures of inspiration) i. A dynamic endoscopic examination is needed in a horse with a history of airway noise during exercise or exercise intolerance but a normal endoscopic examination ii. Beware of horses with lower airway inflammation – look for mucus and do re-breathing examination if suspect! c. Ultrasound for the upper airway is helpful if you have a horse with a thickened and paralyzed arytenoid cartilage that you are unsure of the etiology (chondritis vs. hemiplegia). All right arytenoid cartilages that seem to have limited motion should have ultrasound as chondritis is more common than right sided hemiplegia in the absence of right sided vagal nerve damage (e.g. from injection). i. Transverse view of larynx should show a trumpet shaped arytenoid cartilage. Horses with chondritis have a thickened triangular looking cartilage. Some calcification in the arytenoid cartilage body is normal. 4. If you detect an abnormality with the paranasal sinuses: a. Hallmarks are nasal discharge coming from the sinus drainage angle, or foul-smelling nasal discharge with eating problems that may indicate dental disease. Horses with sinus disease may have distortion of the nasal passages or distortion that extends into pharynx in severe or chronic cases. b. Radiographs are the best tool for field diagnosis of sinus disease. Ensure that 4 views (DV, lateral, both obliques) are taken. Putting the side of interest closest to the plate helps. c. When reading the radiographs align it how the horse was standing so that any fluid lines will be horizontal. This makes them easier to see. d. Different angles for the obliques will help to pick off the problem. Sometimes the tooth roots are difficult to assess if there is fluid in the paranasal sinuses. These cases are good candidates for referral (sinus drainage + radiographs, sinoscopy, CT). If referral is not an option sinus trephination for sinus drainage may improve radiographs. Recommend discussing with your referral center. 5. Surgical techniques for the upper airway: a. Laryngeal, pharyngeal and guttural pouch problems that need surgery will need referral. It is very common that dynamic pharyngeal or laryngeal problems in sport horses or back-yard horses are linked to lower airway inflammation. If the results of your endoscopy, re-breathing examination +/- BAL point to lower airway inflammation, medical management can be tried first. b. It is important to know how to do a tracheostomy in the field!! This can give you more time to assess a patient with severe upper airway disease, or allow it to be transported to a referral center for further work-up. It is done standing with a line-block. Often the horses are so compromised that they will stand willingly for it without sedation. If you do need sedation, give small amounts and wait 5 minutes between doses as over-sedation could make the respiratory obstruction worse when pharynx relaxes. i. Video of temporary tracheotomy: https://www.youtube.com/watch?v=Q7U9-AEMF8U c. Sinus trephination techniques are helpful for providing more information for owners who do not want to refer: i. Biopsy to assess if neoplasia ii. Drainage of sinus to aid radiographic contrast (repeat oblique views) iii. Sinus lavage after cheek teeth extraction: 08, 09 = rostral maxillary sinus, 10, 11 = caudal maxillary sinus 1. The conchofrontal trephination site is the easiest and will access the CMS a. Access to the RMS if the maxillary septal bulla is fenestrated 2. Alternatively, for the RMS you can do an RMS trephine. Advantage of chonchofrontal trephination with fenestration of maxillary septal bulla is that you will avoid nerves and soft tissue at the RMS trephination site and establish an alternate route of drainage while the sinus heals. iv. If you have performed a trephination for treatment of sinusitis and the problem does not resolve in 2 weeks then referral recommended – there may be infection in another sinus compartment that is difficult to access or there may be another underlying problem .

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