Page 322 - Clinical Small Animal Internal Medicine

290 Section 4 Respiratory Disease

Table 29.1 Common diseases affecting the upper airway tomography with rhinoscopy. Arterial blood gas analysis
VetBooks.ir Site Examples commonly identifies hypoxemia with hypercapnia.

Nares Stenotic nares Lower Airway
Nasal cavity Inflammation, neoplasia, infection (bacterial,
fungal, parasitic), granuloma, foreign body The lower airway is composed of the intrathoracic
Pharynx Neoplasia, polyp, abscess, granuloma, elongated trachea, primary and lobar bronchi, and bronchiolar
soft palate, foreign body, stenosis/stricture arborization. Dogs may be affected most commonly by
Larynx Paralysis, collapse, neoplasia, abscess, granuloma, intrathoracic tracheomalacia, bronchomalacia, and
everted saccules, foreign body chronic bronchitis, while feline patients are most com-
monly diagnosed with asthma. Foreign body obstruction
must be considered. While neoplasia may affect the
develop severe secondary hyperthermia. Patients lower airway, they rarely induce acute dyspnea due to
affected by upper airway disorders should always be han- their chronic, insidious nature. Owners may report a
dled with minimal restraint, as they may experience res- chronic and/or progressive history of coughing that is
piratory arrest with minimal manipulation. frequently productive although the sputum is most often
Patients with upper airway diseases with partial obstruc- swallowed. Affected patients commonly have a respira-
tion should be given appropriate sedation and supplemen- tory pattern characterized by prolonged expiration
tal oxygenation as soon as possible in an effort to reduce despite normal inspiratory time and effort; additionally,
the work of breathing and anxiety. The least stressful a clinician may observe abdominal effort during expira-
method of supplemental oxygen provision should be tion (abdominal push) and/or auscultate expiratory
employed, and viable options include flow‐by, facemask, wheezes. Patients may display orthopnea, and feline
oxygen cage, nasal cannulation, modified Elizabethan col- patients may breathe with an opened mouth. A murmur
lar (i.e., Crowe collar), and transtracheal catheterization. is not expected unless lower airway disease has contrib-
A commonly used sedative protocol for cardiovascularly uted to the development of cor pulmonale. Tracheal
unstable patients is the combination of a pure mu opioid sensitivity may be noted in dogs with tracheobron-
(i.e., fentanyl 2–4 μg/kg IV; oxymorphone 0.05–0.1 mg/kg chomalacia and chronic bronchitis.
IV/IM; methadone 0.2–0.5 mg/kg IV; hydromorphone Feline bronchial asthma is a common respiratory
0.1–0.2 mg/kg IV) with a benzodiazepine (i.e., diazepam condition caused by altered immunosensitivity of the
0.1–0.5 mg/kg IV; midazolam 0.2–0.4 mg/kg IV). respiratory tract to inhaled allergens. This hyperrespon-
Acetylpromazine (0.02–0.1 mg/kg IV/IM) and butorpha- siveness causes various structural and chemical changes
nol (0.1-0.2 mg/kg IV/SQ) may be appropriate for cardio- in the tracheobronchial tree, including adrenergic–
vascularly stable patients. cholinergic imbalance and abnormal mucus production.
While provision of sedation and supplemental oxygen is No pathognomonic clinical signs and/or laboratory
sufficient to relieve clinical signs for many patients with assays have been identified, and definitive diagnosis is
upper airway diseases, some will not meaningfully based on history, physical examination findings, and
respond. These patients must have their airways captured exclusion of other disease entities from the list of differ-
via orotracheal intubation immediately, and the astute cli- ential diagnoses.
nician must be prepared to perform an emergency trache- The cause of canine chronic bronchitis is not defini-
ostomy for those patients with complete oropharyngeal tively known, and is typically considered idiopathic in
and/or laryngeal obstruction. Passive and active cooling nature. Establishment of a clear link between this disease
measures should be employed for patients with body tem- and environmental pollutants, hypersensitivity reactions,
peratures greater than 40.5 °C (105 °F), but should be dis- and/or poor dental health has been challenging.
continued with body temperatures reach 39.4 °C (103 °F). Accordingly, a definitive diagnosis is currently made with
Once stable, a thorough physical examination should documentation of lower airway inflammation and elimi-
be performed in an effort to determine the underlying nation of other potential causes. Tracheobronchomalacia
cause of the upper airways signs (if not obvious). is characterized by progressive flaccidity of the tracheal
Diagnosis of specific airway abnormalities in an individ- cartilages that results in collapse of the tracheal and/or
ual patient requires thorough evaluation of the nares, bronchial lumina. The definitive cause of this disease has
oral and nasal pharynx, and larynx. Diagnostic investiga- not yet been identified, and possible contributing factors
tion may include a sedated orolaryngeal examination, include airway allergies inducing chronic inflammation,
aural and otoscopic examination, thoracic and cervical genetic predisposition, and cartilage matrix degenera-
radiography, tracheal fluoroscopy, and nasal computed tion. During exhalation, the intrathoracic trachea and/or