Page 666 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.2 Surgical conditions of the respir atory tr act 641

VetBooks.ir found in flat racing, followed by National Hunt, then 3.79
eventing, show jumping and dressage. A grade of II.1
or lower is usually considered within normal limits,
and treatment for RLN is only indicated if further
diagnostics determine a more serious problem (i.e.
marked muscular atrophy or preferably dynamic
endoscopy evidence). Grade II.2 and III.1 RLN usu-
ally have normal exercise tolerance and treatment for
vocal cord collapse may be used if clinical signs are
compelling (see Vocal cord collapse, p. 654). Grades
III.2 and higher are usually significant and result in
collapse of the arytenoid cartilage during strenu-
ous exercise. There is a poor correlation between
the degree of RLN observed at rest, and the ability
of the horse to maintain abduction of the arytenoid
cartilage at exercise. Thus, treatment should always
be guided by careful assessment of the clinical signs,
the degree of muscular atrophy, the character of Fig. 3.79 Collapse of the left arytenoid cartilage
the respiratory noise at exercise and, if possible, by over to the right side of the larynx during exercise.
endoscopy during exercise.
Grades III.3 and IV RLN are usually associated The complications of tie-back surgery are impor-
with severe respiratory obstruction at exercise and tant. A permanent implant is used and if infection
surgery is necessary for all but the most sedentary were to localise on the suture then removal would be
horses. the only effective treatment. Infection may be asso-
Many surgical procedures have been tried for ciated with poor surgical technique or, more likely,
RLN. Hobday/Williams procedure (ventriculec- penetration of the airway during placement of the
tomy /cordectomy) is reviewed under Vocal cord ligature, particularly at the cricoid. Multifilament
collapse (p. 654). Only laryngoplasty (tie back) and materials are much more prone to infection than
neuromuscular pedicle grafting will be reviewed monofilament materials such as nylon (Fig. 3.80).
here (permanent tracheotomy is also appropriate in Postoperative dysphagia is a frequent complication.
some cases and is discussed under Emergency air- It has been shown that sham surgery with removal of
way obstruction, p. 661). Arytenoidectomy is also the ligature results in some dysphagia, thus surgical
advocated in some situations and is reviewed under scarring and neural damage from the dissection will
Arytenoid chondritis (p. 643). have some effect on deglutition. The fixed abduction
The laryngoplasty or tie-back procedure has been of the arytenoid cartilage is a likely cause of dyspha-
used for over 30 years, and for all the many failings gia. The degree of dysphagia is very variable and is
of the surgery, there are few more practical alter- not directly correlated with the degree of abduction.
natives. The procedure involves the placement of a It is recommended always to feed horses from the
suture on the dorsal surface of the larynx between ground following laryngoplasty, and to feed damped
the cricoid cartilage and the muscular process of the food with a more ‘sticky’ consistency. Fresh grass is
arytenoid. It is intended that the suture mimics the one of the most difficult materials to swallow and
action of the cricoarytenoideus dorsalis muscle in a any horse suffering significant postoperative dys-
partially contracted position. Two sutures are usu- phagia should be prevented from grazing. Following
ally used, to mimic the action of the two separate a tie back almost all horses will cough occasionally
bellies of this muscle. It is usually combined with a during eating. Occasional horses will develop inter-
ventriculocordectomy. It may be performed under mittent pyrexia and occasionally frank pneumo-
general anaesthesia or in the standing sedated horse. nia (Fig. 3.81). Removal of the implant is usually