Mechanisms of Edema

Lecture 8

Water consitutes what percentage of body weight?

60%

How much water is intracellular?

2/3

How much water is extracellular?

1/3

What percentage of extracellular water is in the interstitium?

80%

What percentage of extracellular water is intravascular?

20%

How does water shift from different compartments and into and out of the cells?

concentration gradients

Water distribution between plasma and the interstitium is determined mainly by what?

osmotic and hydrostatic pressure differentials between the compartments

What is hydrostatic pressure?

the difference between the pressure within the capillaries and the pressure within the interstitium

What is the most important plasma protein responsible for the oncotic pressure gradient?

albumin

What is the interstitium’s major oncotic protein?

glycoproteins

Plasma proteins make up 1% of the osmolality but represent the majority of the onccotic pressure gradient, why?

there is a vast difference in the concentration of these proteins between the interstitium and plasma

What is the name of the equation that represents how water moves?

Starling’s forces

Define edema.

excessive interstitial fluid

Alterations in any of the factors which regulate normal fluid distribution resulting in fluid accumulation in the interstitium results in what?

edema

What are the four mechanisms of edema?

• increased microvascular permeability

• increased intravascular hydrostatic pressure

• decreased oncotic/osmotic pressure

• decreased lymphatic drainage

Explain the mechanism of increased microvascular permeability.

• inflammation resulting in release of mediators to cause vasodilation

• vasodilation results in widening of the interendothelial gaps

• water moves from the intravascular space into the interstitium whcih creates the tissue swelling we often see in inflammation

Septicemia can cause what?

generalized edema

What are the mechanissm of increased intravascular hydrostatic pressure?

• increase blood flow (hyperemia)

• passive accumulation of blood (congestion)

• increased blood volume

True or false: increased intravascular hydrostatic pressure can be localized or generalized.

True

What occurs due to an atrial septum defect (large hole between right and left atrium)?

right side compensates and undergoes hypertrophy which then creates equal pressures and leads to congestive heart failure

Tracheal froth is an indication of what?

pulmonary edema

What is tracheal froth?

frothy white/pink fluid in airway

Which sided heart failure leads to cavitary effusions (liver, thorax, abdomen) and backs up into venous bloodflow (systemic)?

right

Which sided heart failure leads to pulmonary edema and backs up into the pulmonary circuit (lungs)?

left

What causes back up in heart failure?

decreased hydrostatic pressure

True or false: cardiac disease usually starts on one side and becomes bilateral as it progresses.

true

What can cause a centrilobular/reticular pattern?

fibrosis

What sided heart failure causes chronic passive hepatic congestion?

right

Where is albumin produced?

liver

What causes decreased oncotic pressure?

decreased plasma proteins; hypoalbuminemia (decreased albumin)

What are mechanisms of hypoalbuminemia that result in edema?

• severe blood loss

• protein losing enteropathy

• protein losing nephropathy

• severe burns

• loss of hepatic functional mass

• profound malnutrition (emaciation)

When a pet is in liver failure, they cannot produce albumin which means they cannot maintain what?

oncotic pressure

Which mechanism of edema is responsible for bottle jaw?

Haemonchus contortus (sucks blood; found in abomasum) causes decreased oncotic pressure ????

What can you see when viewing the lungs affected by pulmonary edema?

• white froth from main stem bronchi

• space between interlobular septae due to fluid presence

Why does equine GI lymphoma have a corrugated appearance to mucosal surface?

neoplastic cells thickening mucosa which results in the gut being unable absorb well and you lose albumin/protein from “leaky gut”

How do you distinguish equine hepatic cirrhosis from nutmeg liver?

by ruling out heart failure and/or histologic evaluation (heart failure = nutmeg liver)

Equine heaptic cirrhosis results from what?

end stage liver disease

What is equine hepatic cirrhosis?

hepatic structure is replaced by fibrosis

What causes decreased lymphatic drainage?

• lymphatic vessel compression due to neoplasia or inflammation

• lymph vessel constriction from fibrosis

• lymph vessel blockage due to thrombus or embolus

In congenital lymphedema, the lymphatic vessels are either ____ or ____.

hypoplastic, aplastic

Define anasarca.

everything is edematous

Define effusion.

when fluid accumulates in a body cavity (abdomen, thorax, pericardial sac)

What are the three categories of effusions?

• pure transudate

• modified transudate

• exudate

Which category of effusion has low protein and low cellularity?

pure transudate

Which category of effusion has high protein and high cellularity?

exudate

What type of effusion do we see in hypoalbuminemia?

pure transudate

Which type of effusion do we see in heart failure?

modified transudate

What type of effusion do we see in inflammation?

exudate

What prefix do we use with only pure transudate effusions?

hydro-

Transudative effusions are a result of one of two mechanisms, what are these two mechanisms?

• increased intravascular hydrostatic pressure

• decreased oncotic/osmotic pressure

What is ascites?

abdominal transudative effusion, hyproperitoneum

Exudative effusion are a result of what?

increased vascular permeability due to inflammation

What is the specific type of effusion (typically thoracic) due to obstruction of the thoracic duct (impairment of lymphatics)?

chylous effusions

Chylous effusions have what color fluid?

opaque white to pink