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Human Diseases > 17.2 Venous thromboembolism and anticoagulants > Flashcards

17.2 Venous thromboembolism and anticoagulants Flashcards

1
Q

What does the term venous thromboembolism refer to?

A

Venous thromboembolism refers to deep vein thromboses and pulmonary emboli.

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2
Q

What are anticoagulants used to treat?

A
  • DVT
  • PE
  • Atrial fibrillation (irregular synchrony of the atria which can lead to thrombi forming in the heart)
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3
Q

What score is used to determine a patient’s risk of a DVT?

A

Wells score
<2 = DVT unlikely
2 or greater = DVT likely

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4
Q

How is a DVT confirmed?

A

Using a venous doppler ultrasound

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5
Q

If a patient has a Wells score of 2 or above how should they be managed?

A
  • Injection of LMWH until diagnosis is confirmed by doppler
  • If doppler is positive, begin oral anticoagulants with vit K antagonist or novel oral anticoagulant
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6
Q

Name risk factors for thrombosis.

A
  • Recent surgery
  • HRT
  • Combined oral contraceptive pill
  • Inactivity/bedridden
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7
Q

Briefly outline clot formation.

A

Soluble fibrinogen converted to insoluble fibrin strands via a complex enzyme cascade in which zymogen precursors and activated by serine proteases.

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8
Q

What is Virchow’s triad?

A

Describes the 3 factors favoring thrombus formation.
- Stasis of blood flow: long haul flight, immobilised person
- Hypercoagulability: e.g. certain hormone therapies or pts with certain cancers
- Endothelial injury: damage to the venous system

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9
Q

How are patients undergoing surgery managed with regards to VTE risk

A
  • After undergoing surgery patients are given a low dose of prophylactic anticoagulant to prevent VTE
  • For patients who actually have VTE, they are given a higher dose after surgery which is a treatment dose rather than a prophylactic dose
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10
Q

What percentage of the general population are moderate to high risk for VTE?

A

2%

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11
Q

What percentage of DVTs are asymptomatic?

A

3.7-26%

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12
Q

What are the 2 types of heparins used in anticoagulant therapy?

A
  • LMWHs: low molecular weight heparins
  • UFHs: unfractionated heparins
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13
Q

When are LMWHs used?

A

When anticoagulant therapy is initiated.
Subcutaneous injection.
Does not require regular blood tests unlike UFHs.
Predominantly acts on factor Xa.
Also used in cancer treatment.

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14
Q

When are UFHs used?

A

For higher risk patients.
Requires IV administration and hospital admission.
APTT or KCCT blood test used.
Act on factor Xa and IIa.

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15
Q

What are the differences between LMWHs and UFHs?

A

LMWHs: average molecular weight of 4-6000 Daltons
UFHs: 15000Daltons

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16
Q

What agent is used to reverse the actions of UFHs?

A

Protamine
Protamine is not as effective in reversing actions of LMWHs.

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17
Q

Name a common LMWH and its side effects.

A

Enoxaparin
Side effects:
- Bleeding
- Heparin induced thrombocytopaenia

17
Q

Name a common LMWH and its side effects.

A

Enoxaparin
Side effects:
- Bleeding
- Heparin induced thrombocytopaenia

18
Q

What is heparin-induced thrombocytopaenia?

A

An immune mediated adverse reaction to heparin.
Caused by HIT antibodies of IgG class.
- Platelet factor 4 binds to heparin
- Antibody-heparin-PF4 complex leads to increased platelet activation
- Thrombosis formation in arteries and veins
- Leads to skin necrosis and injection site, acute systemic reaction, possible limb ischemia
- Discontinue heparin

Assessed using T4 score

19
Q

What is the management following a suspected PE?

A
  • Initial anticoagulation with LMWH until diagnosis is confirmed by CT pulmonary angiogram (CTPA)
  • Anticoagulation with VKA (warfarin) or NOA for 6 months
20
Q

Is a pulmonary embolism serious?

A

Yes, extremely high mortality rate (30-40,000 a year in England and Wales)

21
Q

What is the most common Vit K antagonist?

A

Warfarin (99% of pts on VKA are on warfarin)

22
Q

What are the 2 enantiomers of warfarin?

A

s-warfarin
r-warfarin

23
Q

Describe the action of warfarin.

A
  • Rapidly absorbed and completely bioavailable
  • Has a delayed onset of action
  • Long half life (36 hours)
  • Typical starting dose of 2-5mg per day
24
Q

What is a major possible adverse effect of warfarin?

A

Haemorrhage

25
Q

What type of patient cannot have Warfarin?

A

Pregnant women or those trying to get pregnant.

26
Q

What is the antidote for warfarin?

A

Vitamin K

27
Q

Describe the actions of vitamin K antagonists.

A
  • VKAs enhibit the enzyme epoxide reductase
  • This prevents Vit K synthesis
  • Reduction of vit K dependent clotting factors:
  • II
  • VII
  • IX
  • X
  • Protein C
  • Protein S
28
Q

How long does a pt need to take warfarin before they obtain full anticoagulation?

A

5 days.
During this period pts also need to be covered by additional LMWHs.

29
Q

How does warfarin dose change with age?

A

Older patients require a lower dose.

30
Q

What system is used to monitor patients taking warfarin?

A

INR
- International system
- Prevents excessive anticoagulation
- Helps to predict maintenance dose

31
Q

What is the normal therapeutic INR for patients taking warfarin?

A

2.0-3.0

32
Q

Why do patients need to have their INR checked when prescribed antibiotics by a dentist?

A

Antibiotics are likely to interact with warfarin.

33
Q

What INR indicates high risk of spontaneous bleeding?

A

4.0 and above.

34
Q

How is warfarin reversed?

A
  • For patients with a major bleed: begin with 5mg IV Vit K and dried prothrombin complex
  • For patients with INR greater than 8 but no bleeding: 1-5mg Vit K, restart warfarin when INR is less than 5
35
Q

What are the supportive measures for all major hameorrhage?

A
  • Resuscitation with haemorrhage control
  • Tranexamic acid 1g every 8 hours
36
Q

What are the consequences of maternal ingestion of warfarin?

A
  • Craniofacial dysmorphism
  • Low birth weight
  • Short neck and limbs
  • Brachydactyly
  • Stippled calcification, tracheal cartilage calcification, prominent occiput and frontal bossing
37
Q

What are the direct oral anticoagulants (DOACs)?

A

Called DOACs:
- Fewer restirctions than warfarin and don’t require blood monitoring
- Act against factor Xa
- Recommened for prevention of stroke and systemic embolism
- Used for patients with non-valvular atrial fibrillation with one or more risk factors (e.g. prior stroke, hypertension, diabetes, congestive heart failure)

38
Q

Name some DOACs.

A
  • Rivaroxaban
  • Apixaban
  • Dabigatran
  • Edoxaban

All metabolised in different ways and have different renal clearance.

39
Q

How is dabigatran reversed?

A

With Idarucizumab (very expensive)

40
Q

How are DOACs metabolised?

A

CYP3A4 (important metaboliser for apixaban and rivaroxaban)

Human Diseases (47 decks)

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