Laryngeal paralysis is a functional disorder of the larynx resulting in decreased abduction of the arytenoid cartilages during inspiration in dogs and cats. This causes airway obstruction, dyspnea and in some cases life threatening hypoxia. Clinical studies of various aspects of the disorder have improved our understanding of laryngeal paralysis. Key elements of some of these studies are listed and briefly described below.
Esophageal Dysfunction
Barium swallow in a dog with significant esophageal pathology |
Idiopathic laryngeal
paralysis is a disorder affecting more than just the larynx. Studies have
conclusively shown that esophageal motility is abnormal in dogs with laryngeal
paralysis.(1) This is a significant finding for many reasons, not the least of
which is the relationship of esophageal dysfunction with aspiration pneumonia that
commonly occurs after surgical correction by arytenoid lateralization. Dogs with esophageal or gastric
disorders that predispose them to regurgitation can increase their chance of
aspirating and developing pneumonia postoperatively.
When evaluating dogs with
laryngeal paralysis, be sure to get a complete history with emphasis on the
animal’s ability to prehend food and swallow normally. Inquire about any regurgitation
and vomiting. Obtain thoracic radiographs to evaluate for aspiration pneumonia
and megaesophagus. If the dog appears to be a significant risk for aspiration,
consider permanent tracheostomy as an alternative to arytenoid lateralization
to reduce the risk of pneumonia. Metoclopramide can be administered to
laryngeal paralysis dogs as a premedication to reduce the risk of regurgitation
during general anesthesia.
Polyneuropathy
More evidence that laryngeal
paralysis is a complicated disorder affecting multiple organ systems are the
studies showing its association with peripheral neuropathy.(2,3) Several clinical investigations have
documented generalized neuropathy in dogs that have laryngeal paralysis,
emphasizing the need to thoroughly evaluate the neurologic status of these
animals. Owners should be educated about this association, particularly in dogs
that are not obviously affected by neuropathy when first presenting for their
upper airway obstruction. Clinical signs of neurologic deficits may become
evident sometime after treatment of the laryngeal paralysis.
Doxapram
An essential part of the
diagnosis of laryngeal paralysis is the sedated laryngeal exam. Laryngeal
function is assessed by watching the arytenoid cartilages abduct during
inspiration. Since laryngeal function may be affected by the sedative drugs
administered for the examination, a false positive result can occur if the
sedation is excessive. Erratic respirations can also occur, complicating the
assessment. Doxapram has been shown to assist in the exam by stimulating
respiration allowing a more consistent and accurate evaluation of function.(4)
The dosage of doxapram is: 1-5 mg/kg IV.
Minimal Dissection
Lateralization
The original surgical
description of arytenoid lateralization included an extensive amount of
dissection that is no longer felt to be necessary. After completely
disarticulating the crico-arytenoid joint, i.e., the muscular process of the
arytenoid from its articulation to the cricoid cartilage, the sesamoid band
connecting the arytenoids' corniculate processes was also severed. This was a
difficult step in the procedure because of poor exposure and in some cases
resulted in perforation of the pharynx.
Satisfactory lateralization is possible
by simply incising the joint capsule of the crico-arytenoid articulation and
leaving the sesamoid band in tact. Low suture tension has also been shown to be an
effective means of opening the rima glottis compared to high suture tension.(5)
I have used this “minimal dissection” technique for several years now. It
provides for adequate arytenoid abduction, helps to prevent over-correction,
and has lessened the incidence of aspiration pneumonia in my experience.
The “Tie-Back” is Not For All Dogs
Although the arytenoid
lateralization procedure continues to provide satisfactory treatment for many
dogs with laryngeal paralysis, it is contraindicated in dogs that are high risk
for aspiration pneumonia. Owners need to realize that the lateralization
procedure does not make the larynx normal. It opens the airway and relieves
obstruction but the larynx is fixed in its position and not capable of closing.
If the epiglottis cannot completely cover the laryngeal opening during
swallowing, aspiration is likely to occur. Also, as discussed previously, esophageal dysfunction or any other
cause of chronic regurgitation or vomiting (megaesophagus, gastric disorder,
etc.) increases the likelihood of aspiration. In these dogs a permanent
tracheostomy should be considered to relieve the airway obstruction.
A recently performed permanent tracheostomy in a dog. |
For
details on permanent tracheostomy in dogs, see
http://drstephenbirchard.blogspot.com/2014/12/permanent-tracheostomy-in-dogs-life.html.
http://drstephenbirchard.blogspot.com/2014/12/permanent-tracheostomy-in-dogs-life.html.
References
1. BJ. Stanley, JG Hauptman, MC Fritz, et. al.
Esophageal
Dysfunction in Dogs with Idiopathic Laryngeal Paralysis: A Controlled Cohort
Study. Veterinary
Surgery Volume 39, Issue 2, pages 139–149.
2. Orla M. Mahony, Kim E. Knowles, Kyle G. Braund, et.al. Laryngeal Paralysis-Polyneuropathy Complex in Young Rottweilers. Journal of Veterinary Internal Medicine Volume 12, Issue 5, pages 330–337.
3. Braund KG, Shores A, Cochrane S, Forrester D, Kwiecien JM, Steiss JE. Laryngeal paralysis-polyneuropathy complex in young Dalmatians. American Journal of Veterinary Research 1994, 55(4):534-542.
4. Tobias KM1, Jackson AM, Harvey RC. Effects of doxapram HCl on laryngeal function of normal dogs and dogs with naturally occurring laryngeal paralysis. Vet Anaesth Analg. 2004 Oct;31(4):258-63.
5. S Bureau, E Monnet. Effects of Suture Tension and Surgical Approach During Unilateral Arytenoid Lateralization on the Rima Glottidis in the Canine Larynx Veterinary Surgery Volume 31, Issue 6, pages 589–595.
2. Orla M. Mahony, Kim E. Knowles, Kyle G. Braund, et.al. Laryngeal Paralysis-Polyneuropathy Complex in Young Rottweilers. Journal of Veterinary Internal Medicine Volume 12, Issue 5, pages 330–337.
3. Braund KG, Shores A, Cochrane S, Forrester D, Kwiecien JM, Steiss JE. Laryngeal paralysis-polyneuropathy complex in young Dalmatians. American Journal of Veterinary Research 1994, 55(4):534-542.
4. Tobias KM1, Jackson AM, Harvey RC. Effects of doxapram HCl on laryngeal function of normal dogs and dogs with naturally occurring laryngeal paralysis. Vet Anaesth Analg. 2004 Oct;31(4):258-63.
5. S Bureau, E Monnet. Effects of Suture Tension and Surgical Approach During Unilateral Arytenoid Lateralization on the Rima Glottidis in the Canine Larynx Veterinary Surgery Volume 31, Issue 6, pages 589–595.
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