Chapter 11 - Interstitial edema

Question 1

What are the most common conditions associated with interstitial edema formation (5)? Give relevant disease processes for each

Answer 1

• Venous hypertension (heart disease, venous thrombosis)
• Hypoproteinemia (protein-losing enteropathy and nepherectomy)
• Increased microvascular permeability (inflammation, infection)
• Impaired lymph flow (trauma, surgical damage, systemic venous hypertension, anesthesia)
• Inflammatory edema (inflammation, anaphylaxis, burn injury, frostbite)

Question 2

Give the Starling-Landis equation modeling the microvascular filtration rate.

Answer 2

Jv = LpA [(Pmv - Pint) - σd (πp - πint)]

Jv: microvascular filtration
Lp: hydraulic conductivity
A: filtration surface area
Pmv and Pint: hydrostatic pressures within the microvessels and interstitial space
σd: osmotic reflexion coefficient
πp and πint: colloid osmotic pressure exerted by plasma and interstitial fluid

Question 3

How does the glycocalyx affect the Starling-Landis principle?

Answer 3

1. Endothelial glycocalyx acts like a primary barrier to microvascular filtration
2. Oncotic gradient between intravascular and interstitial spaces is in reality set between the plasma and the glycocalyx rather than being trans-endothelial. Colloid osmotic pressure is lower within the protein-free glycocalyx fluid than within the interstitial fluid, thus increasing ∆π.
   (3. In physiologic conditions, the glycocalyx retains a high reflection capability for albumin because of the high density of negative electric charges of its GAG side chains)

(see “Glycocalyx and sepsis-induced alterations in vascular permeability” Crit Care. 2015; 19(1): 26. )

Question 4

In which tissue are found the lowest σd (high protein permeability) and highest σd (low protein permeability)?

Answer 4

Lowest σd (high protein permeability): liver

Highest σd (low protein permeability): brain

Question 5

Define the Ohm’s law (modeling lymph flow)

Answer 5

QL = (Pint + Ppump - Psv)/RL

QL: lymph flow
Pint: interstitial hydrostatic pressure
Ppump: effective driving pressure generated by the cyclic intrinsic contraction and extrinsic compression of the lymphatic vessels
Psv: systemic venous pressure
RL: effective lymphatic resistance

Question 6

What are the main intrinsic interdependant antiedema mechanisms (4) ?

Answer 6

1. Increased interstitial hydrostatic pressure
2. Increased lymph flow
3. Decreased interstitial colloid osmotic pressure
4. Increased transserosal flow in organs within potential place

(Little to no microvascular reabsorption)

Question 7

True or False:
Increased stretch of lymphatic vessels stimulates increased strength and frequency of lymphatic contractions
Increased lymph flow (ex: edema-induced elevation in lymph flow) results in lymphatic relaxation

Answer 7

True - True

Question 8

How does anesthesia contribute to edema formation?

Answer 8

Many anesthetic agents significantly reduce lymphatic pumping and thus increase lymphatic sensitivity to venous hypertension (ex: induced by intravenous crystalloid administration)

Question 9

Which tissue are the most sensitive to an inflammatory-induced interstitial pressure-volume relationship change?

Answer 9

Skin, tracheal mucosa

Question 10

Give two reasons why interstitial edema is hard to predict and manage?

Answer 10

• More than one mechanism of edema formation is often involved
• Disease conditions that last for more than 1 to 2 days can induce adaptative responses i the interstitial fluid balance system that diminish clinical predictive accuracy