Equine Upper Airway Obstruction Flashcards
1
Q
where does most of the airway resistance come from in the equine airway
A
80-90% in upper airway
2
Q
why are horses obligate nasal breathers
A
the soft palate is tightly opposed to the base of the larynx so there is no communication between the oropharynx and the nasopharynx
3
Q
what are the cartilages that make up the equine larynx
A
- cricoid
- thyroid
- epiglottic
- paired arytenoid cartilages
4
Q
label the cartilages of the equine larynx
A
5
Q
what is each arytenoid cartilage composed of
A
two distinct processes
- corniculate process
- muscular process
6
Q
what are the processes of the arytenoid cartilages
A
7
Q
what are the structures of the larynx
A
the visible portions of the arytenoid cartilages are the corniculate processes
8
Q
what is the function of the arytenoid cartilages during swallowing
A
adduct during swallowing and fully abduct at high intesity exercise
9
Q
what are the intrinsic muscles of the larynx (6)
A
- cricoarytenoideus dorsalis
- cricothyroideus
- cricoarytenoideus lateralis
- vocalis
- ventricularis
- arytenoideus transversus
10
Q
label the intrinsic muscles of the larynx
A
- cricoarytenoideus dorsalis (blue)
- cricothyroideus (red)
- cricoarytenoideus lateralis (orange)
- vocalis (yellow)
- ventricularis (green)
- arytenoideus transversus (purple)
11
Q
what is the function of the cricoarytenoideus dorsalis muscle
A
abducts the arytenoids and tenses the vocal cords
12
Q
what nerve innervates the cricoarytenoideus dorsalis muscle
A
recurrent laryngeal nerve
13
Q
what is the hyoid apparatus composed of
A
- paired stylohyoid bones
- certahyoid bone
- thyrohyoid bones
- central basihyoid bone (which has lingual process)
14
Q
label the structures of the hyoid apparatus
A
15
Q
where does the epihyoid sit
A
at junction between the ceratohyoid and stylohyoid and is fused with the stylohyoid
16
Q
what is the function of the hyoid apparatus
A
connects to the skull at the temporohyoid joint
this joint is where the paired largest bones in the hyoid apparatus (stylohyoid bones) articulate with the base of the skull
17
Q
what are the functions of the muscles that attach to the hyoid apparatus
A
contraction of these muscles atler the shape and position of the apparatus which changes position and shape of the larynx and pharyx
18
Q
what are the muscles of the hyoid apparatus
A
19
Q
what are the extrinsic muscles of the larynx (8)
A
- hyoglossus
- genioglossus
- geniohyoideus
- muscles of tongue
- omohyoideus
- sternohyoideus
- sternothyroideus
- thyrohyoideus
20
Q
what do the extrinsic muscles of the larynx attach to
A
onto the basihyoid bone, the lingual process of the basihyoid bone, the soft palate and pharynx
21
Q
what is the function of the extrinsic muscles of the larynx
A
protracts (brings forward) and depresses the tongue as well as pulls the basihyoid bone rostrally which helps increase nasopharyngeal airway size and helps stabilize the walls of the nasopharynx
22
Q
what are the extrinsic larynx muscles shown
A
hyoglossus (green)
genioglossus (pink)
geniohyoideus (yellow)
23
Q
where do the omohyoideus, sternoihyoideus and sternothyroideus attach to
A
a group of muscles in the neck (accessory resp muscles) attach onto the caudal aspect of the thyroid cartilage, the basihyoid bone and the lingual process of the hyoid apparatus
24
Q
what is the function of the omohyoideus, sternohyoideus and sternothyroideus muscles
A
contraction results in caudal traction of the hyoid apparatus and larynx –> dilation and stabilization of the nasopharynx
25
label the extrinsic laryngeal muscles
26
where does the thyroihyoideus muscle attach to
lateral surface of the thyroid cartilage and inserts on the thyrohyoid bone
27
what does contraction of the thyrohyoideus muscle result in
moves the hyoid apparatus caudally or the larynx rostrally and dorsally
helps maintain tight apposition between the soft palate and larynx --\> maintains the soft palate ventral to the epiglottis
28
how do the muscles of the tongue and accessory respiratory muscles work together
help dilate and stabilze the nasopharynx
29
what are the clinical signs of upper resp obstructions
1. noise occuring only during inspiration or expiration at exercise
2. noise occuring during inspiration and expiration only at exercise
3. noise during inspiration and expiration which is evident at rest
30
how does stride rate relate to respiratory rate
during gallop stride rate and resp rate are coupled
inspiration occurs when the limbs are off the ground (flight phase) and expiration occurs when the limbs strike out
31
what are the clinical signs of a horse in respiratory distress (6)
1. loud abnormal resp noises
2. nasal flaring
3. reduced nasal airflow
4. extended and low head position
5. increased resp rate and effort
6. cyanotic mucous membranes
32
what can severe cases of resp distress result in
dsyphagia, nasal reflux of food material and/or a cough
33
what are the steps in evaluating a patient with an abnormal respiratory noise during exercise and showing exercise intolerance
1. patient history
2. clinical exam
3. resting upper airway endoscopy
4. overground endoscopy
34
what are some questions you could ask when getting a concise patient history
1. what is the intended use
2. c/s: what are they? when do they occur? at rest or only during exercise?
3. does the positioning of the head during work have any influence on the noise
4. has the horse had upper resp surgery, or any prev trauma to the neck or upper resp tract
35
what are important steps in the clinical exam
1. carefully auscultate the heart and lungs to rule out CVS disease and lower resp disease as a cause of poor performance
2. palpate throat latch region and neck carefully to assess for signs of prev surgery, trauma and/or jugular vein thrombosis
3. airflow out of both nostrils and note the colour of nasal discharge
36
what can resting airway endoscopy diagnose
1. subepiglottic cyst
2. foreign body
3. arytenoid chondritis
37
is this a normal upper airway on resting endoscopy
yes
38
what is recurrent laryngeal neuropathy (RLN)
inability to fully abduct the corniculate process of arytenoid cartilage **most often the left side**
results in **inspiratory obstruction** of the upper airway
39
what does progressive loss of large myleinated fibres of the recurrent laryngeal nerve cause
neurogenic atrophy of muscles of abduction especially the **cricoarytenoideus dorsalis muscle (CAD)**
40
what is shown here
atrophy of the left cricoarytenoideus dorsalis muscle (CAD)
41
how does recurrent laryngeal neuropathy (RLN) cause exercise intolerance (6)
1. progressive loss of myelinated axons of the recurrent laryngeal nerve
2. paralysis of CAD muscle
3. inability to achieve max abduction of left arytenoid during exercise
4. rima glottis progressively reduces in size
5. hypoxemia, hypercarbia, metabolic acidosis
6. early fatigue and poor performance
42
what causes recurrent laryngeal neuropathy (RLN) (5)
1. most cases are idiopathic and involve large breed horses
2. may be genetic
3. trauma to recurrent laryngeal nerve (perivascular jugular vein injection of an irritant substance such as phenylbutazone)
4. organophosphate toxicity
5. hepatic encephalopathy (disfunction of both arytenoid cartilages)
43
how is recurrent laryngeal neuropathy (RLN) diagnosed with history
**inspiratory whistling during exercise** with variable degree of exercise intolerance ("roaring")
44
what should you do in a clinical exam to assess recurrent laryngeal neuropathy (RLN)
1. auscultate heart and lungs to rule out CVS
2. palpate throat-latch region and neck to assess for signs of prev surgery, trauma and/or jugular vein thrombosis
45
how is recurrent laryngeal neuropathy (RLN) graded during resting endoscopy
degree of abduction that can be achieved with stimulation of the larynx (swallowing)
four point system
46
what is grade 1 recurrent laryngeal neuropathy (RLN)
full and synchronous abduction of the arytenoid cartilages during resting upper airway endoscopy
47
what is grade 2 recurrent laryngeal neuropathy (RLN)
asynchronous movement of arytenoid cartilages but abduction is achieved with stiumlation of larynx
48
what is grade 3 recurrent laryngeal neuropathy (RLN)
asynchronous movement of arytenoid cartilages and full abduction cannot be achieved with stimulation of the larynx
ex. there is still movement in the left corniculate process of the arytenoid cartilage, but it is asynchronous with the right and full abduction cannot be achieved
49
what is grade 4 recurrent laryngeal neuropathy (RLN)
there is complete immobility of the affected arytenoid cartilage and vocal fold
50
can treatment decisions for recurrent laryngeal neuropathy (RLN) be made based soley on findings during resting endoscopy
ideally no
resting doesn't replicate the function of the larynx during exercise and arytenoid function may change with the intro of exercise
overground is best way to assess upper airway dynamics and should be used in conjunction with resting endoscopy
51
how is recurrent laryngeal neuropathy (RLN) graded in overground endoscopy
four point
the degree of arytenoid abduction observed during resting endoscopy doesn't correlate with the degree of arytenoid abduciton during exercise
52
what does grade A of recurrent laryngeal neuropathy (RLN) during overground endoscopy look like
full abduction of the arytenoid cartilages during inspiration
53
what grade of recurrent laryngeal neuropathy (RLN) during overground endoscopy is this
grade A
normal
54
what does grade B of recurrent laryngeal neuropathy (RLN) during overground endoscopy look like
there is partial abduction of the affected arytenoid cartilage during inspiration to a position between full abduction and its positing during resting endoscopy
55
what grade of RLN on overground endoscopy is this
grade B
56
what does grade C of recurrent laryngeal neuropathy (RLN) during overground endoscopy look like
abduction of the affected arytenoid cartilage during inspiration is equivalent to its position during resting endoscopy
57
what grade of RLN on overground endoscopy is this
grade C
58
what does grade D of recurrent laryngeal neuropathy (RLN) during overground endoscopy look like
collapse of the corniculate process into the contralateral half of the rima glottis during inspiration typically with concurrent vocal fold collapse
59
what grade of RLN is this on overgound endoscopy
grade D
60
how do you use resting and overground endoscopy grade systems together
ex. on resting endoscopy there is grade 4 RLN and on overground endoscopy the grade is D --\> overall this horse would be diagnosed with grade 4D RLN when they are combined
61
how is recurrent laryngeal neuropathy (RLN) managed
based on presenting complaint (abnormal upper resp noise, poor perfromance or both)
age
use of the horse
degree of arytenoid abduction during overground endoscopy
62
what is prosthetic laryngoplasty
tie-back
placement of nonasorbable suture prosthesis between cricoid cartilage and muscular process of the affected arytenoid cartilage
the prosthesis allows for permanent abduction of the corniculate process of the arytenoid cartilage
63
when should a prosthetic laryngoplasty be recommended as treatment for a horse with RLN
reserved for horses in which arytenoid collapse is confirmed with dynamic endoscopy and its having a negative impact on performance
64
what are intraop complications can occur with prosthetic laryngoplasty
1. hemorrhage
2. needle breakage
3. perforation of laryngeal or esophageal mucosa
4. cartilage damage by suture
65
what are post op complications that can occur with prosthetic laryngoplasty
1. seroma formation at surgical site
2. surgical site infection
3. incisional dehiscnece
4. dysphagia
5. coughing
6. mild to excessive loss of surgical abduction of arytenoid over time
66
what other conditions can occur with recurrent laryngeal neuropathy (RLN)
vocal fold collapse
67
how do the vocal folds collapse with concurrent recurrent laryngeal neuropathy (RLN)
when there is loss of CAD muscle function and arytenoid collapse there is decreased tension on associated vocal fold --\> predisposing it to collapse during exercise
68
what is occuring here
concurrent vocal fold collapse with recurrent laryngeal neuropathy (RLN)
69
how is vocal fold collapse managed surgically
surgical removal of affected vocal fold(s) and associated laryngeal saccule(s)
## Footnote
**ventriculocordectomy or hobday**
70
what does a ventriculocordectomy do
stabilize the paralyzed arytenoid cartilage and widen the ventral aspect of the rima glottis and decrease respiratory noise associated with RLN
71
when would a ventriculocordectomy be recommended
performed concurrently with tie-back to help maximize airflow dynamics in horses graded C and D on overground endoscopy
or
on its own to reduce abnormal inspiratory noise where the primary owner complaint is noise and arytenoid collapse is mild (grade B)
72
what are post op management changes with ventriculocordectomy or laryngeal palatoplasty
when the arytenoid cartilages are permanelty abducted and vocal fold(s) and ventricle(s) surgically removed --\> predisposing the patient to aspiration of food content
horses should be fed from the floor permanently post op
73
what is the prognosis following surgical treatment in RLN
50-70% of racehorses have improved performance after sugery
75-90% involved in non-racing activities have imrpoved performance after surgery
74
how does reinnervation of the CAD muscle work
isolating the first or second cervical nerve branches (C1/C2) which innervate the omohyoideus muscle and implanting them into the affected CAD muscle to promote reinnervation and hopefully returning muscle function
75
how long does it take to see success after reinnervation of CAD muscle
4-5 months but in some cases 12 months
76
when would reinnervation of CAD muscle be recommended
younger horses with grade B and C laryngeal movements are the best candidates as there is less atrophy than with horses grade D
not suitable for horses that need a quick return to atheletic performance
77
what are the complications of CAD reinnervation surgery
few complications
most common is seroma formation and incisional infection
78
what is the prognosis of CAD muscle innervation
since its a newer procedures there is little published data
but 80% of racehorses showed evidence of reinnervation but only 45% showed improved performance
79
what is partial arytenoidectomy
removal of the corniculate process and body of the arytenoid cartilage
only muscular process of the arytenoid cartilage is left intact
80
when would i recommend a partial arytenoidectomy
very invasive with a high post operative complication rate
it shouldn't be considered as a first-line treatment for RLN
only exception is if there is a congenital malformation of the laryngeal cartilages which would prevent a prosthetic laryngoplasty from being performed
may be recommended for cases in which a prosthetic laryngoplasty has failed due to fracture of laryngeal cartilages, preventing another suture prothesis from being placed
81
what are the complications of partial arytenoidectomy
1. dysphagia occurs in up to 36% of horses
2. edema and hematoma formation at surgical site --\> dyspnea (temporary tracheostomy)
3. long term coughing esp while eating
82
what is the prognosis of a partial arytenoidectomy
60-78% of racehorses return to racing
75% of non-racehorses return to their prev level of use
83
what is dorsal displacement of soft palate (DDSP)
displacement of the caudal free borded of the soft palate dorsal to the epiglottis
84
what are the two types of dorsal displacement of soft palate (DDSP)
1. intermittent
2. persistent
85
what is intermittent dorsal displacement of soft palate (DDSP)
more common
occuring only during exercise
86
what is persistent dorsal displacement of soft palate (DDSP)
rare
observed in resting horses
likely due to neurologic damage secondary to guttural pouch disease or neoplasia
87
what does intermittent dorsal displacement of soft palate (DDSP) result in
**expiratory airway obstruction**
88
when is intermittent dorsal displacement of soft palate (DDSP) more commonly seen
in 2-3 year old thoroughbred and standard bred racehorses
as well as sport horses exercised with their head and neck in flexed position
89
how does intermittent dorsal displacement of soft palate (DDSP) impair performance (4)
1. flow limiting expiratory obstruction
2. increased tracheal expiratory pressure and impedance
3. reduced minute ventilation
4. hypoxia, hypercarbia, impaired athletic performance
90
how does a flexed head position result in intermittent dorsal displacement of soft palate (iDDSP) (5)
1. head and neck flexion
2. alteration in upper airway dimensions
3. increased airway resistance and negative inspiratory pressure
4. instability of soft palate
5. increased susceptibility to dorsal displacement of the soft palate
91
what is the pathogenesis of intermittent dorsal displacement of soft palate (iDDSP)
unknown
50% of cases have concurrent lower airway disease and in some cases evidence of upper airway inflammation
can occur with other disease (epiglottic entrapment)
several muscles or nerves where dysfunction could lead to iDDSP
92
how is intermittent dorsal displacement of soft palate (iDDSP) diagnosed with history
young performance horses with history of sudden impairement in performance often at max exercise (towards end of race)
gurgling upper resp noise or open mouth breathing
93
what is commonly seen in intermittent dorsal displacement of the soft palate (iDDSP)
50% of cases have concurrent lower resp disease
94
when should resting endoscopy be performed in intermittent dorsal displacement of the soft palate (iDDSP)
evaluate airway for any gross abnormalities
its likely you wont see intermittent dorsal displacement of the soft palate (iDDSP) during rest
but conditions such as persistent DDSP can be diagnosed with resting endoscopy
95
what are the conservative treatments of intermittent dorsal displacement of the soft palate (iDDSP)
1. rest from exercise and admin of systemic anti-inflammatories (NSAIDs) if upper airway inflammation present
2. rest from exercise and treatment of lower airway disease if present
3. improve physical condition
4. tack changes
96
what are surgical managements of intermittent dorsal displacement of the soft palate (iDDSP)
1. palatoplasty
2. staphylectomy
3. myectomy
4. laryngeal tie forward
97
when is conservative management of iDDSP indicated
two year old horses are thought to improve spontaneously as they mature
98
what is pharyngeal lymphoid hyperplasia
small foci of lymphoid tissue spread diffusely over the roof and lateral walls of the pharynx
enlargement of these islands of tissue
occurs in young horses due to a combo of immune response and exposure to infection
99
how is phrayngeal lymphoid hyperplasia treated
rest and admin of systemic NSAIDs
done before resorting to surgery for conditions such as iDDSP
100
what is palatoplasty
reduce flaccidity or "tighten" the caudal free border of the soft palate through fibrosis reducing the likelihood of it displacing dorsal to the epiglottis
the soft palate is cauterized with heated steel rods or a diode laser
101
what staphylectomy
0.75cm of the caudal free border of the soft palate is surgically removed
102
what is myectomy
partial resection of the accessory resp muscles
includes sternohyoideus and sternothyroideus with or without omohyoideus or resection of the insertion of the sternothyroideus alone
103
how does myectomy help iDDSP
by resecting the accessory resp muscles
prevent caudal retraction of the larynx helping increase soft palate epiglottis contact and making it harder for the soft palate to flip dirsal to the epiglottis
104
what is laryngeal tie forward
replaces the action of the thyrohyoideus muscle bilaterally
which is to advance the larynx rostrally and dorsally
a non-absorbable suture prosthesis is placed between the thyroid cartilage of the larynx and the basihyoid bone of the hyoid apparatus
105
how does a laryngeal tie forward assist in iDDSP
advances the larynx 4cm rostrally and dorsally --\> increasing soft palate epiglottis contact and making it harder for the soft palate to flip dorsal to the epiglottis
106
what is the prognosis post conservative management in IDDSP
53-61%
107
what is the prognosis of palatoplasty in iDDSP
28-51%
108
what is prognosis of staphylectomy in iDDSP
60%
109
what is prognosis of myectomy in iDDSP
58-71%
110
what is the prognosis of laryngeal tie forward
80-82% initially
55-65% with recent work
111
what is epiglottic entrapment
aryepiglottic folds are bands of mucosa that run from the arytenoid cartilages of the larynx and attach along the free edge of the epiglottis --\> the folds become abnormally positioned above the dorsal epiglottic surface and encompass the epiglottis, resulting in epiglottic entrapment
112
what is shown here
intermittent dorsal displacement of soft palate during exercise
113
what is shown here
pharyngeal lymphoid hyperplasia
114
what is shown here
top is palatoplasty with diode laser
bottom palatoplasty with heated steel rods
115
what is shown here
laryngeal tie forward
116
what is shown here
epiglottic entrapment
the outline of the epiglottis can be seen, the sharp scalloped edges of the epiglottis are not observed
with DDSP you can't see the epiglottis at all
117
how is epiglottic entrapment treated
surgical transection or excision of entrapping treatment
118
what is arytenoid chondropathy
progressive inflammatory chondritis of the arytenoid cartilages typically originating from infection
119
what is the most common manifestation of arytenoid chondropathy
granuloma formation on axial surface of the arytenoid cartilages
results in abnormal inspiratory noise and exercise intolerance
severe cases it may result in complete upper airway obstruction
120
what is seen here
arytenoid chondropathy
granulomas on the axial surface of the left arytenoid cartilage
121
how are arytenoid chondropathy treated
early + mild cases: may respond to medical management, including rest as well as topical and systemic anti-inflammatories (systemic NSAIDs, topical corticosteroids) and systemic antibiotics
but most require excision through a partial arytenoidectomy
if both cartilages are involved --\> permanent tracheostomy
122
what are the most common location of masses and cysts
subepiglottic cysts
123
how are subepiglottic cysts managed
surgical excision
124
what other epiglottic masses can there be
fungal and bacterial granulomas and neoplasia
125
what is tracheal collapse commonly due to
congenital defect in tracheal cartilages in shetland ponies and american mini horses
126
what are the other causes of tracheal collapse
1. paresis of the trachealis muscle,
2. mineralization of the tracheal cartilages
3. lower airway disease (bacterial pneumonia, recurrent airway obstruction)
127
what is secondary tracheal collapse due to
trauma but is uncommon
128
what are the clinical causes of tracheal collapse
intermittent initially and associated with stressful events, exercise and dust, hot weather
over time freq and severity of clinical signs increase
129
what to mild, moderate and severe cases of tracheal collapse present as
mild cases have increased resp rate and exercise intolerance
moderate to severe: audible upper resp noise and may show signs of acute resp distress
130
how is tracheal collapse diagnosed
1. history, signalment, clinical exam and resting airway endoscopy
2. trachea may be localized to one region or significant portion of trachea --\> typically collapses along the dorsal membrane in the region where tracheal rings are incomplete
131
how is tracheal collapse treated
for cases in acute resp distress --\> temporary tracheotomy and oxygen is typically required
not in immediate distress --\> restriction of exercise, mangement of environment, and treatment of any concurrent resp disease
