Page 374 - Small Animal Internal Medicine, 6th Edition

346 PART II Respiratory System Disorders

CRENOSOMA VULPIS
Crenosoma vulpis is a lungworm of foxes that can also infect BOX 22.2
VetBooks.ir dogs. Dogs living in Atlantic Canada and parts of Europe are Underlying Causes of Aspiration Pneumonia in Dogs
most commonly diagnosed with this disease, and the diag-
and Cats*
nosis remains rare in the United States. However, it is pos-
sible that with increased residential development into fox Esophageal Disorders
habitats, the frequency of cases in this country will increase. Megaesophagus, Chapter 29
The worm resides in the airways (i.e., trachea, bronchi, bron- Reflux esophagitis, Chapter 29
chioles). Snails or slugs serve as intermediate hosts. The Esophageal dysmotility, Chapter 29
clinical signs are those of allergic or chronic bronchitis. Tho- Esophageal obstruction, Chapter 29
racic radiographs may have a bronchointerstitial or patchy Myasthenia gravis (localized), Chapter 66
Bronchoesophageal fistulae
alveolar pattern or occasionally a nodular pattern. Infection Localized Oropharyngeal Abnormalities
is diagnosed definitively through identification of the larvae Laryngeal paralysis, Chapter 18
in fecal specimens (using the Baermann technique), tracheal Cleft palate
wash fluid, or bronchoalveolar lavage fluid (see Fig. 20.12, Cricopharyngeal motor dysfunction, Chapter 29
B). Multiple fecal specimens should be examined in sus- Laryngoplasty, Chapter 17
pected cases because the larvae are not always present. A Brachycephalic airway syndrome, Chapter 17
single oral dose of milbemycin oxime (0.5 mg/kg) was effec- Systemic Neuromuscular Disorders
tive in resolving clinical signs and eliminating larvae from Myasthenia gravis, Chapter 66
feces collected 4 to 6 weeks after treatment in 32 dogs Polyneuropathy, Chapter 66
(Conboy, 2004). This treatment may not be effective against Polymyopathy, Chapter 67
immature larvae. As with other pulmonary parasites, the Decreased Mentation
General anesthesia
response to treatment is monitored with thoracic radio- Sedation
graphs and periodic fecal examinations. Post ictus, Chapter 62
Head trauma
Severe metabolic disease
ASPIRATION PNEUMONIA Iatrogenic †
Force-feeding
Etiology Stomach tubes, Chapter 28
A small amount of fluid and bacteria is aspirated from the Vomiting (in Combination with Other Predisposing
oropharynx into the airways of healthy animals, but normal Factors), Chapter 28
airway clearance mechanisms prevent infection. Organisms
from the oropharynx are thought to be the source of bacte- *Discussions of these abnormalities can be found at the given
chapters.
ria in many animals with bacterial pneumonia, specifically † Overzealous feeding, incorrect tube placement, or loss of lower
bacterial bronchopneumonia (see earlier section). In people, esophageal sphincter competence because of presence of tube.
such infection is termed aspiration pneumonia. In veterinary
medicine, the term aspiration pneumonia is generally used to
refer to the inflammatory lung disease that occurs as a result dysfunction (see Chapter 18), and aspiration pneumonia is
of the inhalation of overt amounts of solid or liquid material a complication of therapeutic laryngoplasty. Aspiration
into the lungs. The materials that are usually aspirated are pneumonia can also occur in animals with abnormal pha-
stomach contents or food. Normal laryngeal and pharyngeal ryngeal anatomy resulting from mass lesions, brachycephalic
function prevents aspiration in healthy animals, although airway syndrome, or cleft palate. Bronchoesophageal fistulae
occasionally an excited puppy or a dog running through tall are a rare cause of aspiration pneumonia.
grass aspirates a foreign body. Otherwise, the presence of Aggressive force-feeding, especially in mentally depressed
aspiration pneumonia in an animal of any age indicates an animals, and improper placement of stomach tubes into the
underlying predisposing abnormality (Box 22.2). trachea are iatrogenic causes of aspiration pneumonia.
Aspiration pneumonia is a common complication of Mineral oil administered to prevent hairballs can be a cause
animals with regurgitation. Megaesophagus and esophageal of aspiration pneumonia in cats because the pharynx poorly
dysmotility are the most common causes of regurgitation handles the tasteless and odorless oil.
(see Chapter 29). Other causes of regurgitation (e.g., reflux Damage to the lung resulting from aspiration may stem
esophagitis, esophageal obstruction) are less common. from chemical damage, obstruction of the airways, infection,
Another cause of aspiration pneumonia is localized or sys- and the resulting inflammatory response to each of these
temic neurologic or muscular disease affecting the normal factors. Gastric acid causes severe chemical injury to the
swallowing reflexes of the larynx or pharynx. These reflexes lower airways. Tissue necrosis, hemorrhage, edema, and
can also be depressed in dogs or cats with abnormal levels bronchoconstriction ensue, and a marked acute inflamma-
of consciousness or in those that are anesthetized. Laryngeal tory response is initiated. Hypoxemia resulting from
paralysis has been associated with concurrent esophageal decreased alveolar ventilation and compliance can be fatal.