Wk 8 Flashcards
what is haemostatis
process of coagulation 3 mechanisms vascular spasm platelet plug formation blood clotting (coagulation)
explain the haemostats mechanism: vascular spasm
- When arteries or arterioles are damaged, smooth muscle contained within the walls contract immediately
- Vascular spasm diverts blood away from affected vessel, reducing blood loss
- Last for about 20 minutes on average but can last for hours whilst other haemostatic mechanisms take effect
- Thought to be induced by damage to smooth muscle and acvtivity of pain recpetors
explain the haemostats mechanism: platelet plug formation
- Platelets contact and adhere to damaged parts of the blood vessel, usually the portuding collagen fibres (platelet adhesion)
- When platelets ‘stick’ they become activated
- The structure changes, projections from the membrane stick out and contact other platelets
- They release substances that activate other platelets and maintain vasoconstriction
- Very affective at stopping blood loss from small blood vessels
- End result is fibrinogen bridges between glycoprotein IIb/IIA receptors
explain the haemostats mechanism: blood clotting
- If it escapes it begins to thicken and eventually forms a gel
- The gel separates from the liquid known as serum (plasma minus clotting factors)
- Results in the formation of fibrin threads
- It is a complex process involving many different substances known as clotting factors
formation of a clot
o Formation of prothrombinase (enzyme)
o Conversion of prothrombin to thrombin
o Fibrinogen converts to fibrin (insoluble) by thrombin
forms a fibrin mesh that tightens and pulls damaged vessel together
how is the clotting stopped
- Fibrinolytic system dissolves clots formed
- When a clot is formed, an inactive enxymes called plasminogen is ‘built in’. plasmin digests fibrin threads and stops clotting cascade
what are the actions of anticoagulant drugs
o Prevent coagulation
o Prevent extension of thrombus
o Prevent thromboembolic complications
HAVE NO EFFECT ON ALREADY FROMED BLOOD CLOTS
explain what heparin/low molecular weight heparin is
Heparin
- parenteral anticoagulant
- stops thrombin formation, inhibits clots by binding to antithrombin
- treat venous thromboembolism and prophylaxis
- half-life 1-6 hours
- binds to and inactivates either thrombin (factor 2) or activated factor 10a
- cause bleeding, thrombocytopenia, APTT (activated partial thromboplastin time)
LMW heparin
- only binds to and inactivates activated factor 10a
- fragments of heparin thus smaller
- less clinical effects on clotting cascade = safer
- longer half life
what is warfarin
- oral anticoagulant
- blocks synthesis of vit K dependent factors in coagulation cascade
- peak effects take several days
- INR (2-3)
- used to prevent DVT, AF
- e.g. Coumadin, jantoven, marevan, lawarin
antithrombin III dependent anticoagulant
o Binds to ATIII then neutralises factor Xa by antithrombin
o Inhibtits both thrombin formation and thrombus development
o Prevention of venous thromboembolism
o Long half-life of 17 hours permits once-daily administration
examples of direct thrombin inhibitors and their action
Dabigatran: inhibits fibrinogen to thrombin
Bicalirudin
Lepirudin
Rivaroxiban: oral, fibrinogen to thrombin by binding directly to active site and inhibiting factor Xa
anti platelet drugs and examples
aspirin: Irreversibly combines with platelet COX enzyme, prevents thromboxane A2 production, surpasses platelet aggregation
clopidogrel: Inhibits platelet aggregation, Preventing fibrin links between platelets
glycoprotein: inhibits all pathways of platelet aggregation
What are thrombolytics and contraindications
Dissolve blood clots
- Act on all the fibrinolytic system, convert plasminogen to plasmin
- Given IV
- Short half life of 2min-2hrs
contraindications
• Previous intracranial bleeding at any time
• Stroke in less than a year
• Active bleeding
• Uncontrolled blood pressure (>180 systolic or >100 diastolic)
nursing considerations for chemotherapy include
o Infection o N and V o Dehydration o Pain o Clotting dysfunction o Inhibition of normal cell division • Wound repair • Skin o Diarrhoea o Constipation o Nutrition o Body image o Psychological o Fatigue
