Page 375 - Small Animal Internal Medicine, 6th Edition

CHAPTER 22 Disorders of the Pulmonary Parenchyma and Vasculature 347

Severe respiratory distress can result from physical have aspirated mineral oil. A marked, diffuse alveolar pattern
obstruction of the airways by the aspirated material. In most can be seen in dogs that have severe secondary edema (see
VetBooks.ir cases only small airways are obstructed, but rarely a large the section on pulmonary edema later in this chapter).
The peripheral blood count can reflect the pulmonary
piece of food will obstruct a major airway. Obstruction is
subsequently exacerbated by reflex bronchoconstriction and
examined for the presence of toxic changes suggestive of
inflammation. Inhaled solid material initiates an inflamma- inflammatory process, but it is often normal. Neutrophils are
tory reaction that includes an abundance of macrophages. sepsis.
This response can become organized, resulting in the forma- Tracheal wash is indicated for animals that can tolerate
tion of granulomas. the procedure to identify complicating bacterial infection
Bacterial infection may result from the aspiration of con- and obtain antibiotic sensitivity data. A marked inflamma-
taminated material, such as ingesta that remained in the tory response characterized by a predominance of neutro-
esophagus. Acidic gastric contents are probably sterile, phils is seen in cytologic specimens. Blood resulting from
although in people the contents are considered contami- hemorrhage may be seen in specimens from animals in the
nated if antacids have been taken, if an intestinal obstruction acute period after aspiration. Bacteria may also be seen. Bac-
is present, or if periodontal disease is present. Note that terial cultures should always be performed.
many veterinary patients have periodontal disease. Regard- Bronchoscopy can be used to grossly examine the airways
less of the sterility of the aspirated material, the resultant and detect and remove large solids. However, the likelihood
damage to the lungs by gastric acid predisposes the animal of a large airway obstruction is very small, so bronchoscopy
to the development of a secondary infection. is performed only if clear signs of large airway obstruction
The inhalation of mineral oil elicits a chronic inflamma- are noted (see Chapter 25), or if the animal is not conscious
tory response. Clinical signs in this setting are often mild, and therefore does not require general anesthesia for the
but in rare instances they may be severe. Radiographic procedure.
abnormalities persist and can be erroneously interpreted as Blood gas analysis can be helpful in differentiating
representing neoplastic lesions. hypoventilation from ventilation/perfusion abnormalities
(see Chapter 20), although a combination of abnormalities
Clinical Features is found in most animals with aspiration pneumonia.
Dogs and cats with aspiration pneumonia are frequently pre- Animals with evidence of profound hypoventilation may
sented for acute, severe respiratory signs. Systemic signs such have a large airway obstruction or muscle weakness second-
as anorexia and depression are common, and these patients ary to an underlying neuromuscular disorder such as myas-
may even present in shock. Vomiting, regurgitation, or thenia gravis. Blood gas analysis also assists in the therapeutic
eating may have preceded the onset of distress. Other patients management of these animals and can be used effectively to
are seen because of chronic intermittent or progressive signs monitor the response to therapy.
of coughing or increased respiratory efforts. Occasionally, Diagnostic evaluation is indicated to identify potential
patients show only signs of depression or the predisposing underlying diseases (see Box 22.2). This may include a thor-
disease. A thorough history is obtained, with all organ ough oral and pharyngeal examination, contrast-enhanced
systems carefully reviewed. Owners are specifically ques- radiographic studies to evaluate the esophagus, or specific
tioned about eating behavior (prehension and swallowing), neuromuscular tests.
regurgitation (particularly after eating or drinking), voice
change, force-feeding, and medication administration. Treatment
Fever may be present, but it is an inconsistent finding. Suctioning of the airways is helpful only for animals that
Crackles are often auscultated, particularly over dependent aspirate in the hospital while already anesthetized or uncon-
lung lobes. Wheezes are heard in some cases. Once a patient scious, when it can be performed immediately after aspira-
is in stable condition, a thorough neuromuscular examina- tion. If a bronchoscope is immediately available, suctioning
tion is performed. The ability of the patient to prehend and can be performed through the biopsy channel, which affords
swallow food and water should also be observed. visualized guidance. Alternatively, a sterile soft rubber tube
attached to a suction pump can be passed blindly into the
Diagnosis airways through an endotracheal tube. Excessive suction
Aspiration pneumonia is usually diagnosed on the basis of may result in lung lobe collapse. Therefore low-pressure,
suggestive radiographic findings in conjunction with evi- intermittent suction is used, followed by expansion of the
dence of a predisposing condition. Thoracic radiographs lungs with several positive-pressure ventilations using an
typically show diffuse, increased interstitial opacities with anesthetic or Ambu bag. Therapeutic airway lavage is
alveolar flooding (air bronchograms) and consolidation of contraindicated.
the dependent lung lobes (see Fig. 20.5). Radiographic Animals in severe respiratory distress should be treated
abnormalities may not be apparent until 12 to 24 hours after with fluid therapy, oxygen supplementation, bronchodila-
aspiration, however. Occasionally, nodular interstitial pat- tors, and possibly glucocorticoids. Fluids are administered
terns are seen in chronic cases. Large nodules can form intravenously at high rates to treat shock (see Chapter 28)
around solids; miliary nodules often form in animals that and should be continued after initial stabilization of the