Saturday, February 16, 2013

Feline Pleural Effusions: Diagnosis & Management

Feline Pleural Effusions: Diagnosis & Management
Atlantic Coast Veterinary Conference 2007
Don R. Waldron, DACVS
Virginia-Maryland Regional College of Veterinary Medicine
The pleural space in dogs and cats normally contains only a few milliliters of low protein serous fluid that provides lubrication to pleural surfaces during the motion of respiration. There is a relatively constant turnover of this pleural fluid as a result of hydrostatic and oncotic forces in the systemic and pleural circulatory and lymphatic systems.
Diseases that cause changes in circulatory, lymphatic, plasma oncotic pressure, and capillary permeability may cause disturbances in fluid balance which usually leads to accumulation of excess fluid in the pleural space.
I. Clinical Signs
1.  Dyspnea/Tachypnea:
a.  Usually gradual onset except in traumatic cases
b.  Animal is uncomfortable/unable to rest, won't lie down (orthopnea)
c.  Exercise intolerance
d.  Open-mouthed breathing
e.  Cyanosis
2.  Cough:
a.  Not usually associated with pleural disease but may be seen with underlying cardiac or pulmonary disease
b.  Chylothorax or pleuritis associated with foreign body penetration has been suggested to be more likely to have a cough
3.  Fever:
a.  Usually associated with infectious or inflammatory disease
b.  Occasionally seen with tumors if necrotic
4.  Anorexia/Depression
II. Diagnostics
1.  Physical Examination:
a.  Careful cardiac auscultation
b.  Compressibility of rostral thorax (mediastinal masses!)
c.  Palpation of thoracic inlet
d.  Abdominal palpation
e.  Careful observation of respiratory rate/effort
2.  Radiography/Ultrasonography/Echo:
a.  Caution!! Consider Risk!! Thoracocentesis and/or oxygen administration should be considered prior to radiography.
b.  Consider DV view and standing lateral as patient may be too stressed by lateral recumbency, consider skipping all together if patient is stressed.
c.  Fluid causes loss of cardiac silhouette, diaphragmatic outline loss, blunting of the costophrenic angles and widening of the mediastinum.
d.  Ultrasound may show cardiac function and assist in identifying masses.
e.  Electrocardiogram/Echocardiography useful for ruling out cardiac disease as a cause of effusion.
3.  Thoracocentesis/Fluid Analysis/Blood Work:
a.  Aspiration of fluid from the pleural space may be both diagnostic and therapeutic.
b.  Aseptic preparation preferred and needle is inserted at 5th-8th IC space. Sedation and/or local infiltration of anesthesia may be necessary. A butterfly-needle set attached to an extension tube is very convenient for this procedure.
c.  Fluids are generally categorized based on their protein level, cell counts, and types as transudates, modified transudate, and exudates (septic and non-septic).
d.  Also chylous effusions and hemorrhagic effusions. Many "grey" areas of classification especially with transudates and non-septic exudates.
e.  Air-dried smears, fluid in EDTA tube, and culture of the fluid if microorganisms are seen on cytology may be valuable.
f.  Blood work:
i.  CBC, Chemistry, FELV/FIV, Heartworm test
ii.  Feline Coronavirus antibody?
iii.  Fluid
iv.  Triglycerides & Cholesterol level
v.  PCR on fluid?
vi.  Thoracic Radiographs
vii.  Echocardiography
4.  Differential Diagnosis:
a.  Transudate--Acellular(< 1500nucleated cells/uL and< 3 g/dl of protein) Hypoalbuminemia (< 1.5 g/dL) due to decreased production (liver disease) or excess loss through the GI tract or urine. Early cardiac failure.
b.  Mod Transudate--Moderately cellular (1500-5000 nucleated cells/uL, total protein of approximately 3 g/dl) Chronic cardiac failure, neoplasia, diaphragmatic hernia, lung lobe torsion.
c.  Exudate--Highly cellular (> 5,000 nucleated cells, protein > 3 g/dl).
d.  Non Septic Exudate--FIP, neoplasia, diaphragmatic hernia, lung lobe torsion
e.  Septic Exudate--Pyothorax.
f.  Chylous Effusion--IdiopathicChylothorax, heartworms, neoplasia, congestive heart failure, lung lobe torsion.
g.  Compare triglyceride levels in effusion and peripheral blood. If higher in effusion than peripheral blood = chylothorax.
h.  Hemorrhagic Effusion--Hemothorax, trauma, coagulopathies, neoplasia.
III. Therapeutics
Supportive and symptomatic but must treat primary disease if possible.
1.  Oxygen Administration:
a.  Oxygen may relieve dyspnea and cyanosis.
b.  Delivery via oxygen cage is most desirable and least stressful on the cat.
c.  Oxygen "tents" constructed from plastic bags may be helpful.
2.  Thoracocentesis:
a.  Removal of fluid may restore more normal respiration.
b.  Use of sevo or isoflurane by facemask and intubation is effective and reasonably safe anesthesia; always counsel owner on dangers associated with sedation of the dyspneic patient. Save fluid for diagnostic analysis as mentioned above.
3.  Cage Confinement
4.  Thoracostomy Tube:
a.  Primary therapeutic modality for cats with pyothorax.
b.  General anesthesia and intubation my method of choice.
c.  Clip the lateral thorax generously and prepare for aseptic tube placement.
d.  Make a small (1 cm) skin incision at the 9th or 10th intercostal space.
e.  A Tube-trocar unit (argyle catheter) or surgical instrument is used to tunnel 3-4 intercostal spaces cranioventrally in the subcutaneous space.
f.  Thrust the trocar or instrument in a controlled fashion through the muscle and pleura of the 5th or 6th intercostal space.
g.  Advance the chest tube or red rubber catheter (10-16 French) into the thorax.
h.  Secure with a Chinese finger-trap suture.
i.  Verify proper placement of the tube radiographically prior to recovery from anesthesia, ideally the tube is situated in the ventral thorax with the tip just short of the thoracic inlet.
j.  Intermittent manual drainage 2-3 times daily is performed or the tube is connected to a continuous suction drainage apparatus.
Surgical Disease causing Pleural effusions
1.  Chylothorax:
a.  Rule outcardiac disease, heartworm disease, mediastinal masses.
b.  Conservative therapy with low fat diets, intermittent aspiration, and use of benzopyrene drugs (Rutin, 50-100 mg/kg tid) has been advocated in animals with idiopathic chylothorax.
c.  Thoracic duct ligation and pericardectomyMAY result in complete resolution of the chylous fluid. Prognosis for successful resolution of disease with surgery < 40%. Refer to a surgeon.
2.  Thymoma:
a.  Thymomas in cats appear similar radiographically to the more common lymphosarcoma masses.
b.  FNA of thymomas shows both lymphocytes and epithelial cells.
c.  Complete excision via sternotomy usually produces clinical cure.
d.  Refer to a surgeon.
3.  Diaphragmatic Hernia:
a.  Repair of chronic diaphragmatic hernia is usually straightforward however one must be prepared to do a sternotomy if adhesions are encountered. Usually not necessary but must be prepared and capable of doing if necessary.
b.  Intubation and positive pressure ventilation are required. Do not overly inflate lung lobes!! Remember, the lung lobes have been collapsed for some time and acute inflation may cause pulmonary edema.
c.  I routinely place a thoracostomy tube in all animals with thoracic effusions secondary to chronic diaphragmatic hernias. Usually able to remove within 24-48 hours.
d.  Intensive care coverage needed but surgery is a doable chore if you have surgical interests and are prepared for perioperative care.
4.  Pyothorax:
a.  Usually a surgical disease only in that it requires thoracostomy tube placement.
b.  Primarytherapy is the use of appropriate antibiotic therapy. Perform both aerobic and anaerobic cultures on thoracic effusion. Some have Actinomyces or Nocardia infections.
c.  Appropriate antibiotic therapy should include coverage for aerobes (Clavamox or Baytril) and Metronidazole for the anaerobic component.
d.  Continue the antibiotic therapy for 4-6 weeks assuming positive response.
e.  If animals do not respond within 7-10 days to thoracic drainage and antibiotic therapy thoracic exploration via sternotomy is indicated for debridement and search for foreign body. Fortunately, this is usually not necessary.

Speaker Information
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Don R. Waldron, DACVS
Virginia-Maryland Regional College of Veterinary Medicine
Blacksburg, VA