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CP3 @ UoN - Medicine & Surgery > Haemostasis > Flashcards

Haemostasis Flashcards

1
Q

What lab tests are used to assess the clotting system?

A

Prothrombin Time (PT)
International Normalised Ratio (INR)
Activated Partial Thromboplastin Time (APTT)
Thrombin Time (TT)

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2
Q

Describe PT

A

Tests extrinsic pathway by adding of a tissue factor to patient’s plasma
Prolonged in liver disease/warfarin

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3
Q

Describe INR

A

Ratio of PT to normal control, using international ref preparation
0.9-1.1
Used for warfarin dosing

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4
Q

Describe APTT

A

Tests intrinsic pathway by addition of surface activator to plasma
Used for monitoring of unfractionated heparin

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5
Q

Describe TT

A

Addition of thrombin to patients plasma

Prolonged w/ fibrinogen deficiency/abnormal function/heparin

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6
Q

Where are clotting factors primarily synthesised?

A

Liver

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7
Q

Describe the coagulation cascade

A

Coag cascade - extrinsic and intrinsic pathways activate final common pathway –> fibrin production –> thrombus formation
Thrombin w/ Ca activates FVIII –> stabilises thrombus

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8
Q

What is the role of Vit K in clotting?

A

Cofactor needed for synthesis of blood clotting factors

-II, VII, IX & X (1972) - WEPT

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9
Q

What are the causes of Vit K deficiency?

A

Malabsorptive conditions
Cholestatic jaundice
Antibiotics

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10
Q

What are the physiological inhibitors of coagulation?

A

Anti-thrombin III (serine protease inhibitor, potentiated by heparin)
Activated protein C (generated by vit K, activated by thrombin) –> induces fibrinolysis

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11
Q

Describe fibrinolysis

A

Plasminogen converted to plasmin by TPA
Mediated by thrombin and APC
Plasmin breaks down fibrinogen and fibrin into FDPs

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12
Q

Describe the clinical features, diagnosis & management of inherited bleeding disorders including haemophilia & vWD

A

SEE SURGERY

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13
Q

How does Warfarin work?

A

Inhibits enzyme responsible for regenerating active Vit K

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14
Q

How should Warfarin be monitored intially?

A

Loading dose given w/ INR measure on alternate days

  • takes 5/7 to have an effect on clotting factor levels
  • initial protrombotic effect so combine w/ heparin until INR in therapeutic range
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15
Q

What conditions is Warfarin contraindicated in?

A

Peptic ulcer disease
Bleeding disorders
Severe HTN
Pregnancy

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16
Q

What are the target INRs for prophylactic use of Warfarin?

A

Single DVT/PE = 2-3
Atrial Fibrillation = 2-3
Recurrent DVT/PE = 3-4
Prosthetic metal heart valves = 3-4

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17
Q

What are the NOACs?

A

Novel Oral Anticoagulant Drugs

  • dabigatran
  • apixaban
  • rivaroxaban
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18
Q

What are the NOACs used for?

A

2o prevention in AF pts

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19
Q

How do NOACs work?

A

Rivaroxaban & Apixaban
-reversible comp antagonists of Factor Xa
Dabigatran
-reversible comp antagonist of Thrombin

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20
Q

What are the advantages of NOACs?

A 
Rapid onset of anticoagulant effect
More predictable pharmacokinetics
Lower potential for interactions
No need for routine coag monitoring
Decreased rates of intracranial bleeding
21
Q

What are the disadvantages of NOACs?

A

No specific antidotes for NOACs
Partially cleared by kidney (dose reduction in CKD)
Increased risk of GI bleeding (Dabi & Riva)

22
Q

What should be given to pts on NOACs in the event of a major bleed?

A

Prothrombin complex concentrate (octaplex)

23
Q

Outline the clinical features of DIC, including laboratory tests used in diagnosis

A

SEE SURGERY

24
Q

What determines the management of over anticoagulation w/ Warfarin?

A

INR

Severity of bleed

25
Q

What should be done for over anticoagulation w/ Warfarin if the INR is 4.5-6?

A

Reduce/omit dose of warfarin

Restart when INR <5

26
Q

What should be done for over anticoagulation w/ Warfarin if the INR is 6-8?

A

STOP warfarin

Restart at lower dose when INR <5

27
Q

What should be done for over anticoagulation w/ Warfarin if the INR is >8 w/ no/mild bleeding?

A

STOP warfarin

Give 0.5-2mg oral Vit K if risk factors for bleeding

28
Q

What should be done for over anticoagulation w/ Warfarin in the case of a major bleed?

A

STOP warfarin
Give 5-10mg Vit K (IV)
Give octaplex/FFP (local guidelines)

29
Q

What is the major downside of Vitamin K in reversing Warfarin over anticoagulation?

A

Takes several hours to work

Not sufficient in acute bleed

30
Q

How does Low Molecular Weight Heparin (LMWH) work?

A

Inactivates Factor Xa (not thrombin)

Long acting

31
Q

What are the advantages of LMWH?

A

Given s.c.

No lab monitoring required (can use anti-factor Xa)

32
Q

What are the disadvantages of LMWH?

A

Can accumulate in renal failure

  • lower dose used prophylactically
  • UFH used therapeutically
33
Q

How does Unfractionated Heparin (UFH) work?

A

Potentiates anti-thrombin III
-inc ability to inhibit thrombin, Xa & IXa
Short acting

34
Q

What are the advantages of UFH?

A

Given IV/SC
Anticoag can be terminated rapidly
Useful in severe CKD

35
Q

How is UFH treatment monitored?

A

APTT 6hrly

-aim 1.5-2.5

36
Q

What are the side effects of LMWH/UFH?

A

Bleeding
Heparin Induced Thrombocytopenia
Osteoporosis (long term)
Hyperkalaemia

37
Q

What are the contraindications to LMWH/UFH?

A

Bleeding disorders
Plts <60*10^9
Prev HIT
Peptic ulcer

38
Q

What should be done if a pt is over anticoagulated w/ LMWH/UFH?

A

STOP infusion
Give protamine sulphate
-less effective in LMWH

39
Q

What medications are available for thrombolysis?

A

Streptokinase

Alteplase

40
Q

How does Streptokinase work?

A

Obtained from haemolytic strep

Activates plasminogen to form plasmin

41
Q

What is the main disadvantage of Streptokinase?

A

Antigenic

-precludes repeated use

42
Q

How does Alteplase work?

A

Recombinant tissue type plasminogen activator (t-PA)

  • increased plasminogen activation
  • increased fibrinolysis
43
Q

What is the main disadvantage of Alteplase?

A

Slightly higher risk of intracerebral haemorrhage

44
Q

When are thrombolytic medications used?

A

MI/Stroke

45
Q

What are the contraindications to thrombolysis?

A 
Active bleeding (or signs of cerebral haemorrhage/aortic dissection)
Severe HTN (>200/120)
Recent head trauma
Recent surgery (<2mo)
Pregnancy/recent delivery (<10/7)
Severe liver disease/oesophageal varices
Prolonged/traumatic CPR
46
Q

What is Thrombophilia?

A

Inherited/acquired coagulopathy predisposing to thrombosis

-usually venous

47
Q

What are the caused of Thrombophilia?

A 
Inherited
   -APC resistance/Factor V Leiden mutation
   -Antithrombin III deficiency
   -Prothrombin gene mutation
Acquired
   -APL syndrome
48
Q

What are the indications for Thrombophilia screening?

A 
Arterial thrombosis <50yrs
Venous thrombosis <40yrs w/ no risk factors
Familial VTE
Recurrent unexplained VTE
Unusual site of thrombosis
Recurrent foetal loss (>3)
49
Q

What investigations are appropriate in suspected Thrombophilia?

A 
FBC
Clotting
Fibrinogen +/- APC resistance test
Lupus anticoag/anti cardio-lipin antibodies
Antithrombin &amp; Protein C/S assays
Factor V Leiden/PRothrombin PCR

CP3 @ UoN - Medicine & Surgery (135 decks)

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