Pulmonary and systemic oedema

Question 1

Total body water is 60%of a 70kg male ~42L. What percentage of that is extracellular fluid and interstitial fluid?

Answer 1

1/3 of body water is extracellular fluid ~14L

3/4 of extracellular fluid is interstitial fluid ~11L

Question 2

What is interstitial fluid?

Answer 2

Fluid bathing the body cells which acts as a go between for blood and body cells

Question 3

What determines blood flow in capillaries?

Answer 3

Contractile state of arterioles. Terminal arterioles in most tissue with precappilary sphincters in a few tissue eg mesentary

Question 4

How do different molecules ccross the capillary wall?

Answer 4

1) Water filled pore- small water soluble substances (amino acids, glucose and ions)
2) Endothilial cells= lipid soluble substances (oxygen and carbon dioxide)
3) Vesicular transport = exchangeable proteins

Question 5

Can plasma proteins cross the capillary wall?

Answer 5

No

Question 6

What is ultra filtration?

Answer 6

Exchange of protein free plasma across the capillary wall

Question 7

What determines the net filtration pressure?

Answer 7

Forces favouring filtration - forces opposing filtration (Starling forces)
Filtration coefficient determined by the permeability of the capillary to molecules

Question 8

Starling forces: What are the forces favouring filtration and the forces opposing filtration?

Answer 8

Favouring filtration:
Capillary hydrostatic pressure
Interstitial fluid osmotic pressure
Opposing filtration:
Capillary osmotic pressure (due to plasma proteins)
Interstitial fluid hydrostatic pressure

Question 9

Which are the main staring forces which have the greatest effect?

Answer 9

Capillary hydrostatic pressure

Capillary osmotic pressure

Question 10

Describe the starling forces at the start of the capillary bed which result in filtration?

Answer 10

Capillary hyrostatic pressure is high ~35mmHg due to blood pressure
Capillary osmotic pressure remains constant as plasma proteins cannot leave the capillary ~25mmHg
Net filtation pressure = 36-26 = 10mmHg => flitration

Question 11

Describe the starling forces at the end of the capillary bed which result in reabsorption?

Answer 11

Capillary hyrostatic pressure is low ~17mmHg due to blood pressure falling
Capillary osmotic pressure remains constant as plasma proteins cannot leave the capillary ~25mmHg
Net filtation pressure = 18-26 = -8mmHg => reabsorption

Question 12

During a day filtration exceeds absorption by 2-4 litres. How is excess fluid returned to the circulation?

Answer 12

Lymphatics

Question 13

What are the adaptations of the pulmonary circulation to prevent oedema?

Answer 13

Pulmonary resistance is 10% of systemic resistance
Pulmonary circulation hydrostatic pressure is low 8-11mmHg
Capillary osmotic pressure is still 25mmHg as the plasma proteins cannot leave
Efficient lymph drainage removes any filtered fluid to prevent accumulation

Question 14

What is oedema?

Answer 14

The accumulation of fluid in the interstitial space

Question 15

What are the consequences of pulmonary oedema?

Answer 15

Increase diffusion distance and decrease gas exchange

Reduce lung compliance which will decrease ventilation and reduce gas exchange

Question 16

What are the causes of oedema?

Answer 16

1) Raised capillary pressure
2) Reduced plasma osmotic pressure
3) Lymph insufficiency
4) Changes to capillary permeability

Question 17

Explain how raised capillary pressure causes oedema?

Answer 17

Arteriolar dilation => increased capillary blood flow (side effect of Ca++ antagonists is ankle oedema)
Raised venous pressure => back pressure in capillaries
LVF => pulmonary oedema
RVF => Peripheral oedema
Prolonged standing => damage of venous valves and swollen ankles

Question 18

Explain how reduced plasma osmotic pressure causes oedema?

Answer 18

Normal plasma protein is 65-80g/L. Odema if <30g/L
This is a result of malnutrition, excessive renal excretion of protein, protein malabsorption, hepatic failure (most plasma proteins are made in the liver)

Question 19

Explain how lymphatic insufficiency causes oedema?

Answer 19

Lymph node damage or surgical removal

Filariasis-elephantiasis

Question 20

Why is oedema caused by lymphatic failure usually non pitting?

Answer 20

Because you can’t push the fluid into the lymph vessels as they are damaged blocked (which is what you would do in heart failure)

Question 21

Explain how changes in capillary permeability can cause oedema?

Answer 21

Inflammation, release of histamine, bradykinin and other inflammatory cytokines increase permeability and leakage of proteins decreasing capillary osmotic pressure.

Question 22

What is pulmonary oedema?

Answer 22

Accumulation of fluid in the interstitial and alveolar lung spaces

Question 23

What are the clinical signs of pulmonary oedema?

Answer 23

SOB and crackle on auscletation of the lung bases

Question 24

What are the CZR findings of pulmonary oedema?

Answer 24

Haziness in perihyler region and bases,

Bat wing signs

Question 25

What are some symptoms associated with pulmonary oedema?

Answer 25

Orthopnia and paroxysimal nocturnal dyspnoea