Chapter 105: Thoracic Cavity Flashcards
What is normal plural fluid volume in dogs and cats?
- Dog - 0.1ml/kg
- Cats: 0.3ml/kg
What cells make up normal plueral fluid?
- mesothelial cells
- Monocytes/macrophages
- Lymphocytes
- Neutrophils under 2%
1500-2500 cells/uL
Protein less than 2.5g/dL
What % of dogs have a dorsal thoracic lymph center?
25%
What are the only parts of the body that are NOT drained by the thoracic duct?
- Right thoracic limb
- Right shoulder
- Cervical regions
Drained by the right lymphatic duct
What is the cisterna chyli and where is it located?
- Bipartite, dilated, retroperitoneal lymph channel, ventral to L1-L4 along cranial abdominal aorta
- Most cmmonly sits ventral to L3, caudal to coeliac and cranial mesenteric arteries
What is the major difference in the thoracic duct anatomy in dogs and cats?
- Dogs - travel on RIGHT side through caudal thorax, dorsolateral to aorta.
- Cats: On the LEFT!
Where does the thoracic duct drain into?
Left external jugular vein or jugulosubclavian vein
(Significant anatomical variation - some branches may terminate in azygous)
What embryonic structure forms the thymus?
At what age does it stop growing and starts to involute?
From the 3rd pharyngeal pouch.
4-5 months
What is the normal functional residual capacity (volume of air remaining in lung at end of expiration)
45ml/kg IMPORTANT
What fluid dynamics favor pleural fluid production and absorption?
What is the law that describes this called?
- Increased hydrostatic pressure of systemic and pulmonary capillaries compared to pleural fluid favors pleural fluid production
- Increased osmotic pressure of systemic and pulmonary vascular beds are greater than pleural fluid, favoring absorption
Tends to enter pleural space from parietal pleura and be absorbed by visceral pleura
Starling’s law
What are the functions of the thymus?
Cell mediated immunity
- maturation and selection of T-cells
- Termination of defective or autoreactive thymocytes
Endocrine
- Secretes a whole bunch of hormones for T-cells and enhancement of immune function
How do you classify pleural transudate, modified transudate and exudate?
Transudate: Protein <2.5, <1500 NCC
Modified: 2.5-5, NCC 1500-<7000
Exudate >3, NCC >7000
What can cause a pure pleural transudate?
- Hypoproteinaemia
- Increased hydrostatic pressure as with CHF (NT-proBNP significantly higher in cats with effusion from heart disease)
*any transudate can become a modified with chronicity
What are differentials for a serosanguinous (modified transudate) effusion?
- Lung lobe torsion
- D-hernia with liver entrapment
- Pericardial effusion
- Right sided heart failure
- Neoplasia (diffuse mesothelioma or carcinomatosis)
- Idiopathic pleuritis
What are differentials for a sanguinous (PCV similar to peripheral blood) effusion?
- Trauma
- Coagulopathy
- Acute lung lobe torsion
- Iatrogenic
- Tumours (chemodectoma, right atrial HSA)
What are differentials for a chylous effusion?
- Any condition that increases hydrostatic pressure in the cranial vena cava
- Trauma to thoracic duct
- Idiopathic (common)
How do you confirm chylothorax?
***Triglycerides higher and cholesterol lower than serum
- Chylomicrons in the fluid can be stained with Sudan black
- Positive ether clearance test (ether makes it go away?)
- Modified transudate (protein 2.5-4g/dL, cell count less than 7000/uL, specific gravity less than 1.032)
What are differentials for an inflammatory effusion?
Septic: Pneumonia, trauma, penetrating FB, cervical infections - cats get pneumonia ones from oral flora these are almost always polymicrobial, check for nocardia and actinomyces*
Nonseptic: Hernia or lung torsion, neoplasia, chronic chylous, FIP, pancreatitis
What Intercostal spaces are used for thoracocentesis?
7th-9th
How does inflammatory effusion occur?
Inflammation -> vasodialtion/increased permeability -> fluid
Decreased fluid resorbtion due to increased intrapleural oncotic pressure +/- pleural thickening
How can abdominal issues cause effusion?
Migration through the lymphatics that link the cavities
Traumatic disruption of diaphragm
What is the functional residual capacity of the lungs?
45mL/kg
Minute ventilation is amount of air taken in each minute. What is it determined by?
Tidal volume (volume of each breath) and rate (breaths per minute)
What is included in tidal volume?
Air in alveoli and dead space
