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Basics ⬇

Basics

Definition

Abnormal accumulation of fluid within the pleural cavity

Pathophysiology

  • More than normal production or less than normal resorption of fluid.
  • Alterations in hydrostatic and oncotic pressures or vascular permeability and lymphatic function may contribute to fluid accumulation.

Systems Affected

  • Cardiovascular
  • Respiratory

Signalment

Species

Dog and cat

Breed Predilections

Varies with underlying cause

Mean Age and Range

Varies with underlying cause

Predominant Sex

Varies with underlying cause

Signs

General Comments

Depend on the fluid volume, rapidity of fluid accumulation, and the underlying cause.

Historical Findings

  • Dyspnea
  • Tachypnea
  • Orthopnea
  • Open-mouth breathing
  • Cyanosis
  • Exercise intolerance
  • Lethargy
  • Inappetence
  • Cough

Physical Examination Findings

  • Dyspnea-respirations often shallow and rapid
  • Muffled or inaudible heart and lung sounds ventrally
  • Preservation of breath sounds dorsally
  • Dullness ventrally on thoracic percussion

Causes

High Hydrostatic Pressure

  • CHF.
  • Overhydration.
  • Intrathoracic neoplasia.

Low Oncotic Pressure

Hypoalbuminemia-occurs in protein-losing enteropathy, protein-losing nephropathy, and liver disease.

Vascular or Lymphatic Abnormality

  • Infectious-bacterial, viral, or fungal.
  • Neoplasia (e.g., mediastinal lymphoma, thymoma, mesothelioma, primary lung tumor, and metastatic disease).
  • Chylothorax (e.g., from lymphangiectasia, CHF, cranial vena caval obstruction [sometimes associated with transvenous pacemaker implantation], neoplasia, fungal infections, heartworms, diaphragmatic hernia, lung lobe torsion, trauma).
  • Diaphragmatic hernia.
  • Hemothorax (e.g., from trauma, neoplasia, coagulopathy, Angiostrongylus vasorum).
  • Lung lobe torsion.
  • Pulmonary thromboembolism.
  • Pancreatitis.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Historical or physical evidence of external trauma-consider hemothorax or diaphragmatic hernia.
  • Fever suggests an inflammatory, infectious, or neoplastic cause.
  • Murmurs, gallops, or arrhythmias combined with jugular venous distension or pulsation suggest an underlying cardiac cause.
  • Concurrent ascites suggests FIP, CHF (mainly dogs), severe hypoalbuminemia, diaphragmatic hernia, disseminated neoplasia, or pancreatitis.

  • In cats, decreased compressibility of the cranial thorax suggests a cranial mediastinal mass.

  • Concurrent ocular changes (e.g., chorioretinitis and uveitis) suggest FIP or fungal disease.

CBC/Biochemistry/Urinalysis

  • Hemogram results may be abnormal in patients with pyothorax, FIP, neoplasia, or lung lobe torsion.
  • Severe hypoalbuminemia (generally <1 g/dL to cause effusion) suggests protein-losing enteropathy, protein-losing nephropathy, or liver disease.

  • Hyperglobulinemia (polyclonal) suggests FIP.

Other Laboratory Tests

  • Fluid analysis should include physical characteristics (i.e., color, clarity, odor, clots), pH, glucose, total protein, total nucleated cell count, and cytologic examination; Table 1 provides characteristics of various pleural fluid types and their disease associations.

  • In cats the LDH concentration in transudates is <200 IU/L and in exudates it is >200 IU/L.
  • Pleural fluid pH <6.9 suggests pyothorax in cats.
  • Glucose concentration in pleural fluid usually parallels levels in serum. In cats, pyothorax and malignancy lower pleural fluid glucose concentration relative to serum glucose concentration; thus, pleural fluid with a normal pH and low glucose concentration suggests malignancy in cats.
  • Serologic tests for feline leukemia virus (if patient has mediastinal lymphoma), feline immunodeficiency virus (if patient has pyothorax), and coronavirus (if FIP is suspected) are available.
  • Cardiac disease suspected-consider a heartworm test in dogs and cats and a thyroid evaluation in cats.
  • Infection suspected-do aerobic and anaerobic bacterial culture and sensitivity tests and consider special stains (e.g., gram and acid-fast stains) of the fluid.
  • FIP suspected-consider protein electrophoresis of the fluid; γ -globulin level >32% of total protein strongly suggests a diagnosis of FIP.
  • Chyle suspected-do an ether clearance test or Sudan stain of the pleural fluid, and triglyceride and cholesterol evaluations of the fluid and serum.

Imaging

Radiographic Findings

  • Used to confirm pleural effusion; should not be performed until after thoracocentesis in dyspneic patients with evidence of pleural effusion on physical examination.
  • Evidence of pleural effusion includes separation of lung borders away from the thoracic wall and sternum by fluid density in the pleural space, fluid-filled interlobar fissure lines, loss or blurring of the cardiac and diaphragmatic borders, blunting of the lung margins at the costophrenic angles (ventrodorsal view), and widening of the mediastinum (ventrodorsal view).
  • Rounding of the caudal lung lobe borders (lateral view)-most common in patients with fibrosing pleuritis caused by chylothorax, pyothorax, or FIP.
  • Unilateral effusion-most common in patients with chylothorax and pyothorax; hemothorax, pulmonary neoplasia, diaphragmatic hernia, and lung lobe torsion.
  • Evaluate post-thoracocentesis radiographs carefully for cardiomegaly, intrapulmonary lesions, mediastinal masses, diaphragmatic hernia, lung lobe torsion, and evidence of trauma (e.g., rib fractures).
  • Can diagnose a diaphragmatic hernia with positive-contrast peritoneography.
  • Can evaluate the thoracic duct by positive contrast lymphangiography.

Echocardiographic Findings

  • Ultrasonographic evaluation of the thorax is recommended whenever cardiac disease, diaphragmatic hernia, or cranial mediastinal mass is suspected.
  • Echocardiography is easiest to perform before thoracocentesis, provided the patient is stable.

Diagnostic Procedures

  • Thoracocentesis-allows characterization of the fluid type and determination of potential underlying cause.
  • Exploratory thoracotomy or thoracoscopy-to obtain biopsy specimens of lung, lymph nodes, or pleura, if indicated.

Treatment ⬆ ⬇

Treatment

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

  • Treatment varies with specific disease.
  • Diuretics generally reserved for patients with diseases causing fluid retention and volume overload (e.g., CHF).

Precautions

  • Avoid drugs that depress respiration or decrease blood pressure.
  • Inappropriate use of diuretics predisposes the patient to dehydration and electrolyte disturbances without eliminating the effusion.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

Radiographic evaluation is key to assessment of treatment in most patients.

Possible Complications

  • Death due to respiratory compromise.

  • Reexpansion pulmonary edema may develop after pleural effusion is manually removed.

Expected Course and Prognosis

Vary with underlying cause, but usually guarded to poor. In a study of 81 cases of pleural effusion in dogs, 25% recovered completely and 33% died during or were euthanized immediately after completing diagnostic evaluation.

Miscellaneous ⬆

Miscellaneous

Synonyms

  • Hydrothorax = transudates and modified transudates
  • Pyothorax = empyema, septic pleuritis

See Also

See “Causes”

Abbreviations

  • CHF = congestive heart failure
  • FIP = feline infectious peritonitis
  • LDH = lactate dehydrogenase
  • LSA = lymphoma
  • PMN = polymorphonuclear cell
  • RBC = red blood cell

Author Francis W.K. Smith, Jr.

Consulting Editors Larry P. Tilley and Francis W.K. Smith, Jr.

Client Education Handout Available Online

Suggested Reading

Cahalane AK, Flanders JA, Steffey MA, Rassnick KM. Use of vascular access ports with intrathoracic drains for treatment of pleural effusion in three dogs. J Am Vet Med Assoc 2007, 230:527–531.

Mellanby RJ, Villiers E, Herrtage ME. Canine pleural effusions: A retrospective study of 81 cases. J Small Anim Pract 2002, 43(10):447–451.

Sherding RG, Birchard SJ. Pleural effusion. In: Birchard SJ, Sherding RG, eds., Saunders Manual of Small Animal Practice, 3rd ed. St. Louis, MO: Saunders Elsevier, 2006, pp. 1696–1707.

Smeak DD, Birchard SJ, McLoughlin MA, et al. Treatment of chronic pleural effusion with pleuroperitoneal shunts in dogs: 14 cases (1985–1999). J Am Vet Med Assoc 2001, 219(11):1590–1597.