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Pleural Space Disease

Pneumothorax* = air
Chylothorax* = lymph
Pyothorax* = pus
Hemothorax = blood
Hydrothorax = "water" - pure transudate
Diaphragmatic hernia = organs


Radiographic signs of pleural effusion

1. Gravity dependent soft tissue opacity
2. Fissure lines in the lungs


Pleural space

1. Pleura: thin layer of mesothelial cells
- visceral pleura covers lung surface
- parietal pleura lines thoracic wall, diaphragm, mediastinum
- small amount of fluid between layers normally (helps lungs expand when thorax expands)

2. Pleural fluid volume determined by:
- Starling's forces (hydrostatic and oncotic pressure)
- Lymphatic drainage
- Mesothelial cells


Potential pleural effusion mechanisms

1. Increased venous hydrostatic pressure (ie. CHF, thrombosis)
2. Decreased oncotoic pressure
3. Impairment of lymphatic drainage (increased venous pressure, lymphatic trauma, neoplasia, lung lobe torsion)
4. Increased vascular permeability


Pleural effusion: physical exam

Pattern of dyspnea:

- Muffled ventrally (gravity dependent fluid)

Pneumothorax: muffled dorsally, echo-like (air bubble rises)


Pleural Effusion: other physical exam parameters

1. Other cardiopulmonary abnormalities (including jugular pulses)
2. Thoracic compression (ie. cat mediastinal mass)
3. Peripheral LN
4. Abdominal palpation: masses, pain, ascites
5. Fever
6. Mucous membranes
7. Cranial nerves (space occupying mass putting pressure on nerves causing Horner's syndrome)
8. BCS/muscle condition


Pleural Effusion (first step)

1. Respiratory distress?
==> Yes = thoracocentesis
==> No = Thoracic imaging, minimum database



1. Sternal (ideal, not required; gravity dependent fluid will be symmetrical)
2. Insert
- ~7-9th intercostal space
- Air: aim for 2/3rd the way up between CCJ and spine
- Fluid: may need to aim closer to CCJ
- Insert needle in front of rib (vessels and nerves lie caudal to ribs!!)
3. Ultrasound-guidance helpful for effusions

(often you can make a patient feel a lot better by just tapping one side)



1. Insert needle bevel up
2. W/ needles:
- Once in chest, raise hand UP (allows needle to rest against body wall w/ bevel OUT - allows fluid to be pulled in)


Thoracocentesis: volume removed

1. Save samples of effusion
- Note total volume removed
- EDTA tube: preserves cell morphology for cytology
- Red top: various biochemical tests
- Culture tubes (aerobic and anaerobic)
- +/- PCV if hemorrhagic (*if peripheral PCV is same as effusion PCV, indicates bleeding into pleural space - hemothorax*)


Effusion Classification

1. Transudate
- Protein ~0.0 g/dL
- TNCC < 2500/uL

2. Modified transudate
- Protein ~2.5 g/dL
- TNCC ~2500 - 5000/uL

3. Exudate
- Protein > 5 g/dL
- TNCC > 5000/uL


Pleural effusion: transudates

1. Low protein, low cellular pleural fluid
2. Usually caused by low oncotic pressure
- Hypoalbuminemia
DDx: Hepatopathy (decreased liver function), PLE, PLN
3. *Or increased hydrostatic pressure from early heart failure
- Over time the heart failure transudates turn into modified transudates


Pleural effusion: modified transudates

Modified transudates
1. Transudates that have been "modified" by the addition of: cells, protein, and/or chyle
- Right sided heart failure, pericardial disease
- Neoplasia (lymphoma, mesothelioma, carcinoma, etc)
- Chylothorax
- Lung lobe torsion
- Idiopathic


Pleural effusion: exudates

1. High protein, high cellular effusions
2. Predominant cell type depends on underlying cause
- Infectious (bacterial, fungal)
- Neoplasia
- Chylothorax
- Lung lobe torsion


Biochemical tests

1. Triglycerides
- Definitive dx of chylothorax: fluid TG > serum TG
(chyle = fat and WBC's)
2. Glucose
- Low in septic effusions
3. pH
- Low in septic effusions


Thoracic imaging

1. Radiographs
- Confirm pleural effusion (masks soft tissue lesions!)
- sometimes you may want to do thoracocentesis, drain the fluid and repeat radiographs
- May help determine etiology (cardiomegaly, mediastinal mass, lymphadenopathy)
2. Thoracic ultrasound
- Pleural fluid acoustic window
- Pleural thickening, masses, abscess
3. Thoracic CT
- Neoplasia, abscesses, foreign body


Pleural fluid and neoplasia

Neoplasia is a frequent cause of pleural effusion!*
1. Tumors affecting any one of the following locations
- Visceral/parietal pleura, lungs, mediastinum, LN/lymphatics
2. Varied fluid types: modified transudate (or exudate), chylous


Pleural fluid and neoplasia: Dx

Dx: identify cells on fluid cytology
- Most common w/ round cell neoplasia (lymphoma - they usually flake off the best)
- Absence of a dx on fluid cytology
- Imaging (ultrasound - thorax AND abdomen, CT)
NOTE: abdomen is easier to biopsy/aspirate than is the thorax
- +/- surgery for exploration and biopsy
- thoracoscopy
- thoracotomy



1. Hemorrhage into the pleural space
2. Causes
- Trauma
- Neoplasia
- COAULOPATHY (rodenticide!!!)*
- Vessel rupture
- lung lobe torsion, heartworms, Spirocerca lupi (all not super common)


Hemothorax: dx

1. Effusion PCV roughly equals peripheral PCV
2. Effusion should NOT clot (platelets and clotting factors get taken back up by pleural surfaces quite quickly!)
3. Effusion contains:
- Macrophages
- NO platelets


Hemothorax: tx

1. Only tap if necessary to alleviate dyspnea
- Body will absorb RBC's
- May make worse if coagulopathy present
2. Assess coagulation status
- PT and PTT
3. Treatment depends on underlying cause
- Vit K and blood products for rodenticide toxicity
-Surgery may be indicated if bleeding mass