Page 409 - Small Animal Internal Medicine, 6th Edition

CHAPTER 25 Emergency Management of Respiratory Distress 381

(see Chapter 18). Other laryngeal and pharyngeal diseases obstruction typically exhibit the greatest breathing effort
are listed in Boxes 16.1 and 16.2. Severe tracheal collapse can during expiration, which is generally prolonged relative to
VetBooks.ir result in extrathoracic or intrathoracic large airway obstruc- inspiration. The most common cause of intrathoracic large
airway obstruction is collapse of the mainstem bronchi
tion, or both. Rarely, other diseases of the extrathoracic
trachea, such as foreign body, stricture, neoplasia, granu-
Chapter 21). A high-pitched, wheezing, cough-like sound is
loma, and hypoplasia, result in respiratory distress. and/or intrathoracic trachea (tracheobronchomalacia; see
Patients with extrathoracic airway obstruction often often heard during expiration in these patients, and crackles
present with acute distress in spite of the chronic nature of or wheezes may be auscultated. Other differential diagnoses
most of these diseases, because of a vicious cycle of increased include foreign body, advanced Oslerus infection, tracheal
respirations leading to increased obstruction, as described in neoplasia, tracheal stricture, and bronchial compression by
Chapter 16. This cycle can almost always be broken with extreme hilar lymphadenopathy.
medical management (Fig. 25.1). The patient is sedated (see Sedation, oxygen supplementation, and minimization of
Table 25.1) and provided a cool, oxygen-rich environment stress as described for the management of extrathoracic
(e.g., oxygen cage). For dogs with brachycephalic airway syn- airway obstruction are often effective in stabilizing these
drome, morphine is given. Otherwise, acepromazine is used. patients as well. High doses of hydrocodone or butorphanol
Subjectively, dogs with brachycephalic airway syndrome will provide cough suppression and sedation (see Chapter
seem to have greater difficulty maintaining a patent airway 21). Dogs with chronic bronchitis may benefit from bron-
when sedated with acepromazine compared with morphine. chodilators and corticosteroids.
Short-acting corticosteroids (e.g., dexamethasone, 0.1 mg/
kg intravenously) are thought by some to be effective in PULMONARY PARENCHYMAL DISEASE
decreasing local inflammation. Diseases of the pulmonary parenchyma result in hypoxemia
In rare cases, sedation and oxygen supplementation will and respiratory distress through a variety of mechanisms,
not resolve the respiratory distress, and the obstruction including obstruction of small airways (obstructive lung
must be physically bypassed. Placement of an endotracheal disease; e.g., idiopathic feline bronchitis); decreased pulmo-
tube is generally effective. A short-acting anesthetic agent nary compliance (restrictive lung disease, “stiff” lungs; e.g.,
is administered. Long and narrow endotracheal tubes with pulmonary fibrosis); and interference with pulmonary cir-
stylets should be available to pass by large or deep obstruc- culation (e.g., pulmonary thromboembolism). Most patients
tions. If an endotracheal tube cannot be placed, a trans- with pulmonary parenchymal disease, including those with
tracheal catheter can be inserted distal to the obstruction pneumonia or pulmonary edema, develop hypoxemia
(see later in this chapter). If a tracheostomy tube is needed, through a combination of these mechanisms that contribute
̇ ̇
it can then be placed under controlled, sterile conditions. to V/Q mismatch (see Chapter 20), including airway obstruc-
It is rarely necessary to perform a nonsterile emergency tion and alveolar flooding, and decreased compliance.
tracheostomy. Animals that present in respiratory distress caused by
pulmonary parenchymal disease typically have a markedly
Intrathoracic Large Airway Obstruction increased respiratory rate (see Table 25.2). Patients with pri-
Respiratory distress caused by intrathoracic large airway marily obstructive disease, usually cats with bronchial
obstruction is rare. Patients with intrathoracic large airway disease, may have prolonged expiration relative to inspira-
tion with increased expiratory efforts. Expiratory wheezes
are commonly auscultated. Patients with primarily restric-
Sedation
Cool environment tive disease, usually dogs with pulmonary fibrosis, may have
Oxygen prolonged inspiration relative to expiration and effortless
Minimal stress
Corticosteroids expiration. Crackles are commonly auscultated. Occasion-
Heat
Excitement ↑ Effort ally, cats with severe bronchial disease will develop a restric-
Exercise tive breathing pattern in association with air trapping and
hyperinflation of the lungs. Other patients, in which a com-
bination of these processes is occurring, show increased
effort during both phases of respiration; shallow breathing;
and crackles, wheezes, or increased breath sounds on aus-
↑ Obstruction ↑ Intraluminal cultation. Differential diagnoses for dogs and cats with pul-
pressures
monary disease are provided in Box 19.1.
Oxygen therapy is the treatment of choice for stabilizing
FIG 25.1 dogs or cats with severe respiratory distress believed to be
Patients with extrathoracic (upper) airway obstruction often caused by pulmonary disease. Bronchodilators, diuretics, or
present in acute respiratory distress because of progressive
worsening of airway obstruction after an exacerbating glucocorticoids can be considered as additional treatments
event. Medical intervention is nearly always successful in if oxygen therapy alone is not adequate.
breaking this cycle and stabilizing the patient’s respiratory Bronchodilators, such as theophyllines or β-agonists, are
status. used if obstructive lung disease is suspected because they