MoD 5 - Haemostasis, Thrombosis And Embolism

Question 1

What 4 things does successful haemostasis depend on?

Answer 1

Blood vessels

• constrict to limit blood loss
• arteries, veins and capillaries.

Platelets

• platelet release reaction occurs and the platelets adhere to the damaged vessel wall and to each other
• ADP and thromboxane A2 cause platelet aggregation

Coagulation

• 1ml of blood can generate enough thrombin to convert all the fibrinogen into fibrin.
• needs tight regulation
• there are thrombin inhibitors
  
  • alpha1antitrypsin and alpha2macroglobulin
  • protein C/S and anti thrombin III

Fibrinolysis

• breakdown of the cross linked Fibrin plaque.
• plasmin is an endogenous enzyme that breaks down the fibrin clots
  
  • can be aided by tPA and streptokinase.

Question 2

What exactly is thrombosis ?

Answer 2

The formation of a solid mass of blood within the circulatory system.

Question 3

Describe Virchows Triad

Answer 3

Endothelial damage
Haemostasis
Hypercoaguability (eg post partum, smokers)

Question 4

Name and describe the possible outcomes of thrombosis

Answer 4

1. Resolution.
   - the clot is completely broken down. This generally occurs only with small clots. Blood flow is restored.
2. Recanalisation.
   - blood flow is re established however it is not complete.
3. Organisation.
   - this is a repair mechanism.
   - infiltration of capillaries and fibroblasts however the lumen still remains occluded to some degree.
4. Propagation
   - the progressive spreading of the the thrombosis.
   - they spread distally in the arteries and proximally in the veins. (Direction of blood flow)

Embolism

• a part of the clot breaks off and lodges at a site that is distant to the site it broke off from.
• as the clot enters the lungs, it can easily get trapped in the capillaries as they are so small here. Hence you get a pulmonary embolism.

Question 5

Not mentioning embolism as an outcome of thrombosis, define embolism.

Answer 5

Blockage of a blood vessel by a solid, liquid or gas at a site that is distant to its origin. (Most are thrombo-emboli).

Question 6

Name a few types of embolism that exist.

Answer 6

Amniotic fluid
Air
Tumour
Medical equipment.

Question 7

Name the classification of pulmonary embolisms and describe their parameters.

Answer 7

Massive - >60% reduction in blood flow. Rapidly fatal

Major - medium size vessels are blocked. The patient will often be SoB, coughing +/- blood stained sputum.

Minor - peripheral arteries are blocked. May be asymptomatic or mild SoB

Recurrent - lots of small and regular pulmonary embolisms can lead to pulmonary hypertension.

Question 8

What are the risk factors for deep vein thrombosis.

Answer 8

Immobility - the veins in the leg return blood back up from the lower limbs. This is aided by the contraction of leg muscles. Immobility reduces the venous return and can therefore predispose to DVT - blood stasis can occur.

Severe burns
Post op
OCP
Post partum

Question 9

What treatment is available to patients who have been identified as being at risk for DVT

Answer 9

Compression hosiery

Heparin

Question 10

Discuss Fat and Cerebral emboli.

Answer 10

Fat emboli
Damage to adipose tissue.
Often seen is fractures of long bones because they contain a lot of bone marrow (itself contains fat). This then enters the blood and it can get lodged somewhere.

Cerebral emboli
The carotids are a common place for atherosclerotic plaques to develop. If an emboli breaks off the plaque, it can easily get lodged in the brain and cause ischaemia. This will be liquefactive necrosis.

Question 11

What is Disseminated Intravascular Coagulation (DIC) ?

Answer 11

Pathological activation of clotting cascade. This forms small clots throughout the body. Blood flow to tissues can reduce and so therefore the patient can end up with multi organ failure.

Patients with DIC can often have uncontrolled bleeding, as all the clotting factors and platelets get used up pathologically so when there is a ‘normal’ response to vessel damage needed, it doesn’t occur so bleeding can easily occur.

Commonly seen in amniotic fluid embolism.

Question 12

What is thrombocytopenia ?

Answer 12

Reduced platelet count

This means there will be a prolonged bleed time.

Question 13

What is thrombophilia ?

Answer 13

This is essentially a form of hypercoaguability.

You are at risk of getting thrombosis.

Question 14

What is haemophilia and what are the two common types?

Answer 14

An X linked recessive genetic condition in which there is uncontrolled clotting mechanisms so there is excessive bleeding.

Factor VIII defiency - haemophilia A
Factor IX deficiency - haemophilia B

Question 15

What is haemostasis essentially a balance of?

Answer 15

A balance between pro-coagulant and anticoagulant forces.