Contributors: Philip Lhermette, Elise Robertson
Species: Canine | Classification: Techniques
Introduction Requirements Preparation Procedure Aftercare Outcomes Further Reading
Introduction
Uses
- 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.
Time Required
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
Decision Taking
Risk assessment
- Low risk unless patient unstable prior to general anesthesia or in respiratory crisis.
- See complications.
Requirements
Personnel
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.
Materials Required
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.
Preparation
Pre-medication
- 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).
Dietary Preparation
- Food should be withdrawn for 6-12 hours to minimize risk of aspiration during the examination.
Restraint
- Light sedation.
Other Preparation
- Preanestheic laboratory tests can be performed as indicated by the patient's age and health status.
Procedure
Approach
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.
- Doxapram hydrochoride Doxapram 0.5-1.0 mg/kg IV administered:
- 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.
Aftercare
Immediate
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).
Long-term
Medication
- As directed by underlying disease process.
Follow up
- As directed by underlying disease process.
Outcomes
Further Reading
Publications
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.