WSAVA Nov 2021 Proceedings - Flipbook - Page 32
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(moderate stenosis) and grade 4 (severe stenosis) are linked to a fourfold
increase in risk of developing BOAS6.
Figure 5. Nostril grading system
Oechtering et al. published on the CT imaging of the brachycephalic nose.
They found abnormal conchal formation in these dogs, with nasal obstruction from a rostrally positioned ventral turbinate and nasopharyngeal
obstruction from caudal aberrant turbinates, originating from the middle
or ventral nasal conchae (seen in 43% of these dogs). The turbinates, in
addition to being abnormally positioned, had a lower level of branching
compared with a normocephalic dog7.
Both severely and mildly affected dogs may have aberrant turbinates, stenotic nares and elongated soft palates to some extent with the severely
affected dogs more likely to have grossly thickened soft palates and other
anatomical changes. This demonstrates how difficult it is to look at lesion
sites independently and we also need to remember that static images on
endoscopy, radiography or CT may be affected by the presence of an ET
tube, phase of respiration, head position and degree of mouth opening,
and thus need to be interpreted with caution.
airflow moving across it.
Figure 6. A trace from WBBP performed on a French bulldog, from these
traces parameters that can be generated include breathing frequency;
total inspiratory volume, time and peak flow; total expiratory volume, time
and peak flow; lags between breath cycles (if any) and hence minute
respiration volume.
This test has been developed to give a BOAS index; a numerical score
from 0–100% to describe how severely an individual dog is affected with
BOAS, where 0% is non-affected and 100% is our most severely affected
individuals2.
The BOAS index is important as we now have an objective measurement
with which to evaluate risk factors for BOAS and the effectiveness of
our surgical treatments, looking at the whole upper airway rather than
individual sections.
Imaging
A major problem with BOAS is that it is often under recognized by both
the public and veterinary professionals. A questionnaire-based study on
disease recognition revealed that approximately 60% of owners did not
perceive their dogs to have airway obstruction when clinical examination
and history were compatible with the disease 5.
As usual in veterinary medicine, this depends on the owner’s budget.
Direct laryngoscopy is sufficient to evaluate the larynx, tonsils and gives a
good idea of soft palate length and thickness. A lateral radiograph of the
skull will allow visualisation of the nasopharynx and soft palate. CT scan
of the head will reveal turbinate morphology and the soft palate thickness.
Rhinoscopy is probably a more accurate method of assessing turbinate
crowding, with a rigid scope used for the rostral nasal cavity combined
with a flexible scope to assess caudal aberrant turbinates, trachea and
bronchi and oesophageal lesions.
For diagnosis we use a functional grading system for BOAS that includes
an exercise test. We exercise the dogs at a moderate trot (4 mph) for 3
minutes and note airway noise, effort, and extreme respiratory signs pre
and post exercise.
CT of the thorax enables assessment of bronchial collapse, aspiration
pneumonia, oesophageal diverticulum and may detect hiatal hernia.
Radiographs of the thoracic cavity may show aspiration pneumonia if CT
is not possible.
When we auscultate these dogs we listen directly over the side of the larynx, not ventrally. We are listening for stertor (awake snoring) and stridor
(higher-pitched noise originating from the larynx).
If finances are very limited, then it is reasonable to treat without imaging.
However, in cases that do not respond successfully to conventional surgery, nasal obstruction or aspiration pneumonia may have been missed.
https://youtu.be/_dADh1gbExs
References
Disease recognition and Functional Grading
https://youtu.be/pQd0xbddfvY
While this system is not perfect, as exercise tolerance may be affected
by ambient temperature and sometimes the animal’s fitness levels, it
does expose those animals that are teetering on the edge of obstruction
when calm and firmly tipped into ‘affected’ once stressed. Exercise tests
also reveal clinical signs in those dogs that only have respiratory noise
when mouth breathing (often the long but not particularly thickened soft
palates) after switching from nasal breathing in the consult room.
We find that about 40% of dogs that show few clinical signs in the consult
room will be classified as affected after the exercise tolerance test8. We
consider no airway noise (grade 0) and mild airway noise (grade 1) as
clinically unaffected as in these dogs we do not detect any decrease in
quality of life, with normal exercise tolerance and no other associated
clinical signs. The grade 2 and 3 dogs have airway obstruction that affects
quality of life and are regarded as clinically affected.
This grading system enables us to advise on treatment – grade 3 dogs
are surgical candidates, grade 2 dogs are likely surgical candidates but if
obese, weight loss could be initiated prior to surgery. We can also monitor
dogs with the grading system and use it in addition to our objective respiratory function test.
In human respiratory medicine, in addition to clinical examination,
respiratory function would be tested with whole-body plethysmography
in conjunction with forced spirometry. The technique that we use for the
extreme brachycephalic breeds dogs is whole body barometric plethysmography (WBBP) where dogs are placed in a sealed chamber with biased
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WSAVA GLOBAL COMMUNITY CONGRESS
• Packer RMA, Hendricks A, Tivers MS, Burn CC, 2015. Impact of Facial
Conformation on Canine Health: Brachycephalic Obstructive Airway Syndrome. PLoS ONE 10(10): e0137496. doi:10.1371/journal.pone.0137496
• Liu NC, Troconis EL, Kalmar L, Price DJ, Wright HE, Adams VJ, Sargan
DR, Ladlow JF.(2017) Conformational risk factors of brachycephalic obstructive airway syndrome (BOAS) in pugs, French bulldogs, and bulldogs.
PLoS One. Aug 1;12(8):e0181928
3. Roedler FS, Pohl S, Oechtering GU, 2013. How does severe brachycephaly affect dog’s lives? Results of a structured preoperative owner questionnaire. Vet J. 2013 Dec;198(3):606-10. doi: 10.1016/j.tvjl.2013.09.009.
Epub 2013 Sep 18
• Poncet CM et al. Prevalence of gastrointestinal tract lesions in brachycephalic dogs with upper respiratory syndrome: clinical study in 73 cases
(2000-2003) . J Small Anim Pract 2005
• Packer, R., Hendricks, A. & Burn, C.C., 2012. Do Dog Owners Perceive the
Clinical Signs Related to Conformational Inherited Disorders as “Normal”
for the Breed? a Potential Constraint to Improving Canine Welfare. Anim
Welfare, 21(1), pp.81–93.
• Liu NC, Troconis EL, Kalmar L, Price DJ, Wright HE, Adams VJ, Sargan
DR, Ladlow JF.(2017) Conformational risk factors of brachycephalic obstructive airway syndrome (BOAS) in pugs, French bulldogs, and bulldogs.
PLoS One. Aug 1;12(8):e0181928
• Oechtering, T., Oechtering, G. & Noeller, C., 2007. Computed Tomo-