Page 367 - Clinical Small Animal Internal Medicine

34 Pleural Effusion 335

Table 34.2 Causes of pleural effusion in dogs and cats Clinical Signs and Physical
VetBooks.ir Physical agents ● Neoplastic disease Examination

Thoracic trauma
Mesothelioma
●
● Electrical burn ● Lymphoma Rapid intervention with minimal patient stress is para-
mount in patients with respiratory distress so it is impor-
● Radiation therapy ● Adenocarcinoma tant to be familiar with clinical signs and physical
● Iatrogenic ● Lymphoproliferative examination findings indicative of certain disease pro-
● Foreign body (e.g., grass syndromes
awn) ● Mesenchymal tumors cesses. Time of onset, volume of fluid accumulation, and
inciting cause of pleural effusion all contribute to the
Lymphatic or venous Infectious disease patient’s history and clinical signs.
obstruction ● Pyothorax (bacterial, fungal) Pleural effusion is a consequence of an underlying dis-
● Lung lobe torsion ● Mycoplasma ease and vague historical clinical signs are often reported
● Diaphgragmatic hernia
including lethargy, exercise intolerance, weight loss, and
Decreased oncotic pressure Extrathoracic disease hyporexia or anorexia. In a retrospective study, tachyp-
● Protein‐losing ● Pancreatitis nea and dyspnea were the most commonly reported
nephropathy ● Peritonitis
● Protein‐losing ● Esophageal rupture complaints by owners, present in 95% of dogs with pleu-
enteropathy ral effusion. Additional complaints, which may or may
● Uroabdomen not be an indication of the underlying disease, include
● Liver failure
cough, polydipsia, vomiting, fever, collapse, diarrhea,
Increased hydrostatic Others restlessness, reluctance to lie down, cervical extension,
pressure ● Feline infectious peritonitis hemoptysis, abdominal distension, melena, hemateme-
● Congestive heart failure ● Coagulopathy (rodenticide sis, and halitosis. Severe pleural effusion may present as
● Heartworm disease or factor deficiency) open mouth breathing and cyanosis, especially if onset
● Thrombosis ● Allergic hypersensitivity is acute.
conditions
● Neoplasia
● Cholecystectomy On physical examination, a restrictive breathing
pattern seen as rapid and shallow breathing has histori-
accumulates, the viscous resistance to flow quickly cally been reported but recent literature suggests an
decreases and the pleural pressure gradient approaches asynchronous (paradoxical) or inverse breathing
the hydrostatic pressure gradient. Both theories contend pattern and decreased lung sounds on auscultation are
that pleural effusion increases pleural pressure by 1 cm more common clinical findings in dogs and cats.
H 2 O/cm effusion height. Paradoxical breathing refers to increased inspiratory
Measuring pleural liquid pressure and pleural surface effort strong enough to pull the abdominal contents
can be challenging because the space is small and the toward the thorax, leading to a sunken flank appear-
insertion of any device will cause an artifact by deforming ance during inspiration and a bulging flank appearance
the surface. In the diseased thorax with an appreciable on expiration. Additional physical examination find-
amount of pleural effusion, these challenges become less ings include muffled heart sounds, decreased ventral
significant and pleural pressure measured is an accurate lung sounds, shallow breathing, and inspiratory dysp-
representation of hydrostatic pressure at the level of the nea. Patients with cardiac disease, such as heart failure,
catheter or transducer. During thoracocentesis or if an pericardial effusion, or caval syndrome, may have a
indwelling thoracostomy tube is in place, pleural pressure murmur or crackles on thoracic auscultation, jugular
can be monitored in veterinary patients with a minimal pulses, a positive hepatojugular reflex, and/or pulse
amount of equipment using a water manometer or pres- deficits. Patients with a coagulopathy causing pleural
sure transducer. If using a pressure transducer, measure- effusion, such as anticoagulant rodenticide toxicity,
ments are recorded in mmHg and should be converted to may have bruising, pale mucous membranes, weak
be interpreted appropriately (1 mmHg = 1.36 cmH 2 O). pulses, or tachycardia on physical examination. Masses
Pleural pressure monitoring may be beneficial with found on abdominal palpation, oral or dermatologic
chronic effusions when draining the effusion does not examination may indicate a neoplastic cause for pleural
necessarily equate to return to normal pleural physiology effusion. Mediastinal neoplasia should be suspected
because the pleural surface remains diseased. If the lungs with an incompressible cranial thorax in cats or Horner
cannot expand appropriately after thoracocentesis, creat- syndrome in cats or dogs. Pain in the right cranial
ing a situation of entrapped lung, the supraphysiologic abdominal quadrant with gastrointestinal signs may be
negative pressure created in the pleural cavity by remov- suggestive of pancreatitis as an underlying cause of
ing the fluid may increase the risk of pneumothorax. pleural effusion (Table 34.3).