MoD Haemostatis And Thrombosis

Question 1

What can blood vessels do to limit blood loss?

Answer 1

Constrict

Occurs in arteries, veins and capillaries

Question 2

What is the role of platelets?

What do they form?

Answer 2

Adhere to damaged vessel wall

Adhere to each other

Platelet plug

Question 3

Describe the platelet release reaction?

Answer 3

ATP –> ADP

ADP, thromboxane A2 causes platelet aggregation

5HT, platelet factor 3 also released

PF3 important in coagulation

Platelets coalesce after aggregation

Question 4

What happens in the coagulation cascade?

Answer 4

Prothrombin is converted to thrombin

Thrombin cleaves fibrinogen to fibrin

Question 5

Why is tight regulation of the coagulation cascade required?

What is it a balance of?

Answer 5

1ml of blood can generate enough thrombin to convert all of the fibrinogen in the body to fibrin

Procoagulant and anticoagulant forces

Question 6

Name four thrombin inhibitors

Answer 6

Anti thrombin 2

Alpha 1 antitrypsin
Alpha 2 macroglobulin

Protein C and S - inherited deficiency

Question 7

What is fibrinolysis?

What happens to plasminogen?

What are the two drugs used in fibrinolytic therapy?

Answer 7

Breakdown of fibrin

Cleaved to plasmin using plasminogen activators

Streptokinase
tPA

Question 8

Define thrombosis

Answer 8

The formation of a solid mass of blood within the circulatory system during life

Question 9

Why does thrombosis occur?

Virchow’s triad

Answer 9

Abnormalities of vessel wall - atheroma, injury, inflammation

Abnormalities of the blood flow - stagnation or turbulence

Abnormalities of blood constituents - smoking, post partum, post op

Question 10

What is the difference in appearance of arterial and venous thrombi?

Answer 10

Arterial - pale, granular, lines of Zahn, lower cell content

Venous - deep red, soft, gelatinous, higher cell content

Question 11

What are the outcomes of thrombosis?

Answer 11

Lysis - complete dissolution of thrombus, fibrinolytic system active, blow flow re-established - most likely when thrombi small

Propagation - spread of thrombosis - distally in arteries, proximally in veins

Organisation - reparative process with in growth of fibroblasts and capillaries. Lumen remains obstructed

Recanalisation - blow flow re-established but usually incompletely. One or more channels formed through organising thrombus

Embolism - part of thrombus breaks off, travels in blood stream and lodges at distal site

Question 12

What are the effect of thrombosis on arterial and venous?

Answer 12

Arterial - infarction or Ischaemia

Venous - congestion, oedema, Ischaemia, infarction (rare)

Question 13

Define embolism

Answer 13

The blockage of a blood vessel by a solid, liquid or gas at a site distant from its origin

90% of emboli are thrombo emboli

Question 14

What are the types of embolism?

Answer 14

Thrombo-emboli

Air
Nitrogen - divers get 'the bends'
Amniotic fluid
Medical equipment 
Tumour cells

Question 15

What happens to thrombo-embolis from

Systemic veins
Heart
Carotid arteries
Atheromatous abdominal aorta

Answer 15

Systemic veins –> Pulmonary emboli

Heart - aorta to the renal, mesenteric and other arteries

Carotid arteries –> brain (Stroke)

Abdominal aorta –> arteries of the legs

Question 16

How can a DVT be prevented?

Answer 16

High risk patients identified and offered prophylaxis

Heparin subcutaneously
Leg compression stocking during surgery

Question 17

What are the risk factors for DVT?

Answer 17

Immobility
Post op
Pregnancy
Oral contraceptives - oestrogen effects coagulation
Severe burns
Cardiac failure
Disseminated cancer

Question 18

How are DVT treated?

Answer 18

IV heparin

Oral warafarin

Stop thrombus getting bigger, don’t dissolve thrombus

Question 19

What is a pulmonary embolism?

What reduction is blood flow is classed as a massive PE?

What happens in a major PE?

What happens in a minor PE?

What do recurrent PEs lead to?

Answer 19

Bit of thrombus that has passed to the lungs where it has got stuck

Massive PE >60% reduction in blood flow, rapidly fatal

Major PE - medium sized vessels blocked, shortness of breath, coughs blood stained sputum

Minor PE - small peripheral pulmonary arteries blocked. Asymptomatic or minor SOB

Hypertension

Question 20

What does successful Haemostasis depend on?

Answer 20

Vessel wall

Platelets

Coagulation system

Fibrinolytic system