6) Haemostasis & Thrombosis

Question 1

Define haemostasis

Answer 1

The body’s response to stop bleeding and blood loss

Question 2

What factors affect haemostasis?

Answer 2

• Vessel wall
• platelets
• coagulation system
• fibrinolytic system

Question 3

What is the function of platelets during thrombosis?

Answer 3

• adhere to the damaged vessel wall
• and to each other using ATP
• forms a platelet plug

Question 4

Describe the factors which control coagulation

Answer 4

• balance between procoagulant and anticoagulant forces
• thrombin +vely feeds back on factors V, VIII and XI
• Inhibition by anti-thrombin 3, ⍺1 anti-trypsin, protein C (deficiencies lead to thrombophilia -excess thombosis)
• Fibrinolysis by plasmin (plasminogen -> plasmin by plasminogen activators)

Question 5

Give an example of a thrombolytic agent, it’s clinical use and method of action

Answer 5

• Streptokinase
• coronary infarction by thrombus post-MI
• enzyme activates conversion of plasminogen -> plasmin
• plasmin causes fibrinolysis

Question 6

Define thrombosis

Answer 6

Formation of a solid mass of blood within the circulatory system during life

Question 7

What factors affect THROMBOSIS?

Answer 7

Virchow’s triad

Question 8

Describe the differences in appearance in thrombi formed in arteries vs veins

Answer 8

Arterial thrombus:

• pale (less RBC:plasma), granular, lines of Zahn, lower cell content

Venous thrombus:

• deep red (high RBC:plasma), soft, gelatinous, higher cell content

Question 9

Describe the difference in effects of thrombus in an artery compared to a vein

Answer 9

Artery:

• ischaemia, infarct (extent dependant on site and collateral circulation)

Vein:

• congestion, oedema, (ischaemia and infarct -when tissue pressure due to oedema > AP)

Question 10

Describe the possible outcomes of thrombosis

Answer 10

• Lysis, (likely when small) complete dissolution and blood re-established
• Propagation, progressive spread of thrombus (distally in arteries and proximally in veins)
• Organisation, repair with ingrowth of fibroblasts and capillaries, lumen remain obstructed
• Recanalisation, blood flow re-established partially via formation of one or more channels
• Embolism

Question 11

Define embolism and give some types

Answer 11

Blockage of a blood vessel by a solid, liquid or gas at a site distant to it’s origin

• Thrombo-emboli (most common)
• Air
• Amniotic
• Nitrogen (Divers Bends)
• Tumour cells
• Medical equipment

Question 12

Describe the possible course (and hence blockage) of a thrombo-embolus originating from the leg

Answer 12

• pulmonary embolus (next point when veins begin to narrow)
• pass into circulation provided R>L shunt, and then:
  
  • atheromatous carotid arteries leading to stroke
  • atheromatous abdominal aorta, blocking arteries to leg

Question 13

Describe the effects of different sized emboli entering the lungs

Answer 13

• MINOR, (small peripheral arteries blocked) asymptomatic or minor shortness of breath
• MAJOR, medium sized vessels blocked, blood in sputum
• MASSIVE (>60% reduction in blood flow), rapidly fatal Recurrent emboli can lead to pulmonary hypertension

Question 14

List some possible causes of DVT and it’s treatment (explaining the action of the drugs quoted)

Answer 14

• immobility, post-op, post-patum, severe burns, cardiac failure, disseminated cancer (any time blood is hypercoaguable)
• INITIALLY with IV heparin (anti-coag, co-factor for anti-thrombin 3)
• LONG-TERM with warfarin (vit-K antagonist so prevents factor production at liver) slower to act -subcutaneous heparin, leg compression and TED stockings

Question 15

DVT is a very common occurence during surgery, descibe possible prophylaxis for this

Answer 15

• subcutaneous heparin
• leg compression
• TED stockings

Question 16

List some different types of emboli and their potential causes

Answer 16

• FAT, long bone fracture, adipose tissue laceration
• CEREBRAL, atrial fibrillation leading to stasis and thrombus formation, can enter brain and cause stroke/TIA
• IATROGENIC, due to treatment (excess air during injection)
• NITROGEN, bubbles form during rapid decompression causing ‘bends’

Question 17

Describe Disseminated Intravascular Coagulation (DIC), it’s symptoms and possible treatment

Answer 17

• Pathological activation of coagulation mechanisms in response to a variety of diseases. (e.g infection, trauma, liver disease, obsteric complications)
• Small clots form throughout the body, disrupting normal coagulation as they use up all the clotting factors.
• Abnormal bleeding occurs from the skin.
• Treatment: Blood transfusion, Anti coagulants

Question 18

What is haemophilia, the types, possible symptoms and treatments

Answer 18

X-R mutation leading to deficiency in a clotting factor, unable to clot

Type A (Factor VIII), type B (Factor IX)

• Haemorrhage into major joints, synovial hypertrophy
• Muscle bleeding causes pressure and necrosis of nerves (painful)
• Can haemorrhage into retroperitoneum / urinary tract

Treat with self-administered factor replacement therapy

Question 19

What is Thrombocytopenia, possible causes, it’s symptoms and treatment

Answer 19

• Platelet count is below the reference range
• Failure of platelet production, increase in platelet destruction, sequestering of platelets
• Usually accompanied by a bone marrow dysfunction, E.g. leukaemia, anaemia
• Lobar Pneumonia
• If it is due to sequestering, cause may be DIC