Laryngoscopy

• Evaluation of laryngeal structure and function.
• Investigation of:
  • Phonation changes (loss of bark or purr).
  • Gagging or coughing during eating or drinking.
  • Stridor.
  • Increased respiratory effort, noisy breathing or cough.
  • Exercise intolerance.
  • Elongated soft palate Soft palate: elongated : should be anticipated and treated at the time of scoping if possible (resection Soft palate: resection ).
  • Laryngeal mucosal edema.
  • Edematous/everted laryngeal saccules (lateral ventricles).
  • Laryngeal paralysis Larynx: paralysis : may be unilateral or bilateral.
  • Laryngeal collapse Larynx: disease overview : a life threatening complication of chronic upper airway obstruction.
  • Laryngeal neoplasia Larynx: neoplasia : lymphoma, squamous cell carcinoma, other carcinomas are the common types.
  • Epiglottic entrapment: secondary to other inspiratory problems, typically very intermittent.

Advantages

• Technically easy procedure.
• Any combination of instruments can be used as long as adequate illumination of larynx is generated.

Disadvantages

• Risk with general anesthetic recovery and may require tracheostomy tube placement Tracheostomy: temporary.

Preparation

• Induction of a light plane of anesthesia Anesthetic induction: overview.

Procedure

• Laryngoscopy can be performed in a matter of minutes. Depends of experience of endoscopist - approximately 1-2 minutes

Risk assessment

• Low risk unless patient unstable prior to general anesthesia or in respiratory crisis.
• See complications.

Veterinarian expertise

• Medium.

Anesthetist expertise

• Medium.
• Needs to be prepared for potential respiratory complications associated with induction, maintanence and recovery from chemical restraint.

Nursing expertise

• Good level of competence required for assisting with and monitoring anesthetic.

Minimum equipment

• Oral speculum.
• Standard intubating laryngoscope and appropriate sized blades.
• OR overhead examination light, pen light, and common wooden tongue depressor to depress the epiglottis.
• Appropriate sized endotracheal tubes Endotracheal intubation in case required to secure a patent airway during anesthesia or recovery.
• Appropriate sized tracheostomy tubes in case required for respiratory compromised patients on recovery (laryngeal paralysis, edema, or masses).

Ideal equipment

• Oral speculum.
• Standard intubating laryngoscope.
• 2.7 or 2.8 mm or 5 mm rigid telescope or 2.5 or 3.5 mm flexible endoscope Flexible endoscopy.
• video monitor for better visualization and for case documentation (still images and video).
• In larger dogs (>7.5 kg) a 5.2 mm bronchoscope or 5 mm rigid endoscope can be used.

Other requirements

• Know what normal anatomy and normal anatomic variations.

• The patient must be under a light plane of anesthesia when assessing laryngeal function:
  • If too deep, the larynx appears paralysed.
• Best not to give patient a narcotic or synthetic narcotic before laryngoscopy:
  • Can induce panting, hypoventilation, and abolish cough reflex.
• Injectable anesthetics most typically used for laryngoscopy.
• A light plane of anesthesia using intravenous propofol Propofol to effect (1 to 4 mg/kg IV) or alfaxalone 2-3 mg/kg to effect Alphaxalone (Alfaxan) :
  • Given slowly over 30 seconds to 2 minutes, to effect.
  • Supplemental mask oxygen.
• Ketamine and diazepam used in combination is an excellent choice in the cat:
  • Intravenous propofol to effect can be used as an alternative to ketamine and diazepam in the cat.
  • Topical 1% lidocaine Lidocaine may occasionally be needed to decrease reflex responses during the procedure (most common in feline patients).

• Food should be withdrawn for 6-12 hours to minimize risk of aspiration during the examination.

• Light sedation.

• Preanestheic laboratory tests can be performed as indicated by the patient's age and health status.

Step 1 - Anatomic examination

• GENTLY depress the epiglottis from the visual field .
• Gently elevate the soft palate as required.
• Pull tongue forward to aid in visualization.
• Soft palate should not extend to the larynx or interfere with respiration.
• Evaluate the cricoid, thyroid, and arytenoid cartilages.
• Evaluate the vestibular folds, vocal folds, laryngeal saccules, epiglottis, and aryepiglottic folds:
  • Normal mucosa light pink and superficial vessels may be visible.
  • Secretions minimal near the normal laryngeal vault.
  • Abnormal findings:
    • Mucosal hyperemia and edema.
    • Excessive secretions.
    • Redundant pharyngeal mucosa.
    • Elongated soft palate, everting laryngeal saccules and accumulation of salivary secretions are common findings in dogs with brachycephalic syndrome.
    • Laryngeal collapse loss of cartilage rigidity secondary to upper airway obstruction in brachycephalic syndrome Brachycephalic airway obstruction syndrome.
    • Laryngeal webbing and granuloma formation secondary to previous surgery or trauma.
    • Both can result in stenosis of glottic lumen.
    • Less commonly, a pharyngeal or laryngeal rannula, tumor, or foreign bodies.

Step 2 - Functional examination

• Monitoring laryngeal adduction, abduction and symmetry of movement:
  • Normal patients arytentoid cartilages should abduct during inspiration and adduct toparamedian position during expiration.
• If laryngeal motion appears abnormal ruling out laryngeal paralysis:
  • Doxapram hydrochoride Doxapram 0.5-1.0 mg/kg IV administered:
    • Increases rate and depth of inspiration.
    • Overrides the potentially depressant effects of anesthesia on laryngeal motion.
• Important for assistant toannouncephase of respiration with each breath and therefore not confuse normal motion with paradoxical motion which can indicate complete laryngeal paralysis:
  • Left, right, or both arytenoid cartilages may have decreased motion (paresis) or not move at all (paralysis) during inspiration.
  • Unilateral and bilateral laryngeal paresis and paralysis occurs in dogs, rarely in cats.
  • Most dogs with laryngeal paralysis have erythematous vocal folds due to turbulent air flow.
  • Cats with laryngeal paralysis may appear soft and floppy with fluttering on expiration.

Monitoring

• Close observation on anesthetic recovery if anatomic or functional laryngeal disease is diagnosed:
• Breathing rate, effort and depth.
• O2 saturation using pulse oximetry Anesthetic monitoring: pulse oximetry.

Analgesia

• Usually not required.

Antimicrobial therapy

• Rarely required.

Potential complications

• Relatively low risk procedure.
• Stimulation of larynx may provoke a very strong vagal response that may result in profound bradyarrythmias:
  • Administering anticholinergic medication before anaesthesia is induced largely prevents this.
• Manipulation of laryngeal mucosa can cause additional mucosal irritation, edema and potentially further narrowing of the airway (complication more common in cats):
  • It is ESSENTIAL for the operator to be very gentle when manipulating this area thus reducing chances of complications due to laryngeal edema and occlusion.
• Some patients with laryngeal disease may have great difficulty maintaining a patent airway during postanesthetic recovery phase:
  • Endotracheal and tracheostomy tubes and instruments should be available (in suspected cases).

Medication

• As directed by underlying disease process.

Follow up

• As directed by underlying disease process.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Creevy K (2009) Airway Evaluation and Flexible Endoscopic Procedures in Dogs and Cats: Laryngoscopy, Transtracheal Wash, Tracheobronchoscopy, and Bronchoalveolar Lavage. Vet Clin North Am Small Anim Pract 39 (5), 869-880 PubMed.
• Noone K E (2001) Rhinoscopy, Pharyngoscopy, and Laryngoscopy. Vet Clin North Amer Small Anim Pract, 31 (4), 671-689 PubMed.

Other sources of information

• Padrid P A (2011)Laryngoscopy and Tracheobronchoscopy of the Dog and Cat.In: Tams T R, Rawlings C A (eds)Small Animal Endoscopy, St Louis, Elsevier Mosby.
• Levitan D, Kimmel S (2008)Flexible endoscopy: respiratory tract.In: Lhermette P, Sobel D (eds)BSAVA Manual of Canine and Feline Endoscopy and Endosurgery, Quedgeley, British Small AnimalVeterinary Association.