Page 325 - Clinical Small Animal Internal Medicine

29 A Respiratory Pattern‐Based Approach to Dyspnea 293

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Table 29.2 Areas evaluated during tFAST and VetBLUE examination
VetBooks.ir tFAST 3 VetBLUE

Right hemithorax Left hemithorax Right hemithorax Left hemithorax
Chest tube site (CTS) Chest tube site Caudodorsal lung lobe (CdLL) Caudodorsal lung lobe
Pericardial site (PCS) Pericardial site Perihilar lung lobe (PHLL) Perihilar lung lobe
Diaphragmatic‐hepatic (DH) Middle lung lobe (MDLL) Middle lung lobe
Cranial lung lobe (CrLL) Cranial lung lobe

Table 29.3 Common etiologies based on thoracic radiographic through the right side of the heart and lodge in the
patterns of distribution pulmonary arterial bed. The caudal lung lobes are more
likely to be involved as they receive most of the right
Pattern of distribution Common underlying etiology ventricular output. Consequences of PTE include hypox-
emia, bronchoconstriction, ventilation–perfusion (V–Q)
Cranioventral Pneumonia, aspiration pneumonitis mismatch, and hyperventilation. With time, further
Perihilar Cardiogenic pulmonary edema (dogs) complications arise, including atelectasis, pulmonary
Caudodorsal Noncardiogenic pulmonary edema, edema, and pleural effusion. Hemodynamic complica-
hematogenous pneumonia tions from PTE depend on the extent to which the
Nodular Pulmonary mycoses, neoplasia pulmonary vasculature is occluded and the amount of
preexisting cardiac and pulmonary compromise. If pul-
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One must understand that VetBLUE and tFAST scans monary vasculature reserve capacity is exceeded, pulmo-
do not replace the diagnostic utility of thoracic radiography nary vascular resistance increases to augment right
ventricular afterload and ventricular oxygen demand.
when evaluating patients with pulmonary parenchymal dis- If the oxygen supply is exceeded, ischemia, dysrhythmias,
ease. Indeed, evaluation of soft tissue parenchymal patterns and/or right ventricular failure may occur. Decreased
may be uniquely helpful in determining the underlying dis- cardiac output is caused by reduced pulmonary venous
ease process (Table 29.3). Interstitial, interstitial‐to‐alveolar, return induced by pulmonary blood flow obstruction.
and alveolar patterns are most commonly reported in Diagnosing PTE is difficult. Clinical signs commonly
patients with pulmonary parenchymal diseases. include tachypnea, dyspnea, and hypoxemia, none of
Animals with primary left‐sided cardiac disease may
have cardiomegaly, left atrial enlargement, and pulmonary which is pathognomonic for PTE. Initial assessment
should include thoracic radiography, abdominal ultra-
venous dilation. While a perihilar radiographic distribu- sonography, arterial blood gas analysis, a complete blood
tion is highly suggestive of cardiogenic pulmonary edema count, biochemical profile, urinalysis and heartworm
in dogs, cats do not have classic radiographic patterns for testing. Reported radiographic abnormalities associated
most parenchymal diseases. The choice of additional diag- with PTE are pleural effusion, regional oligemia, alveolar
nostic investigation should be based on patient history infiltrates, cardiomegaly, hyperlucent lung regions, and
and physical examination. Tracheal washing or bron- enlargement of the main pulmonary artery. While the
choalveolar lavage for airway cytology and culture (bacte- majority of patients with PTE will have radiographic
rial & fungal) may be appropriate for patients with abnormalities, radiographs may also be normal in 9–27%
suspected infectious pneumonia or aspiration pneumo- of dogs and 7% of cats with PTE. Arterial blood gas
nia/pneumonitis. Metastatic screening via abdominal (ABG) analysis is frequently a very useful diagnostic tool.
radiography and/or ultrasonography may be indicated for In one canine PTE study, hypoxemia was documented in
those patients suspected of living with neoplasia, and fun- 80% of affected patients and increased alveolar‐arterial
gal urine antigen and serology should be performed in (A‐a) gradients on room air in all dogs. Basic blood and
those with suspected pulmonary mycoses. Definitive urine testing is performed in an effort to identify predis-
treatment is based on a patient’s ultimate diagnosis.
posing conditions, including hyperadrenocorticism, pro-
tein‐losing nephropathy, protein‐losing enteropathy,
Pulmonary Thromboembolism hypothyroidism, and/or diabetes mellitus.
If these tests fail to identify an underlying disease pro-
Pulmonary thromboembolism (PTE) occurs when cess, echocardiography and measurement of prothrom-
venous thrombi formed in large, deep veins travel bin and partial thromboblastin times may be helpful.