venous thromboembolism Flashcards
how does warfarin (coumarins) work?
inhibit vitamin K dependent carboxylation of factors II, VII, IX and X in the liver
causes a relative deficiency of these coagulation factors
how is the dosing of warfarin calculated for patient?
monitored by the international normalised ratio (INR) derived from the prothrombin time
takes around 5 days to establish maintenance dosing
loading regimens assist early dosing
individual dose for each patient- ethnicity affected
dietary intake of vitamin K affects warfarin dose
what is the most common side effect?
bleeding
major bleeds occur in 1% of patients each year
risk of fatal intracranial haemorrhage 0.25% per annum
how to reverse warfarin in a patient?
depends on whether the patient is bleeding
vitamin K: oral or intravenous routes
reverse by administering deficient clotting factors
what are the two methods of venous thrombosis prevention?
mechanical: foot pumps, compression stockings
pharmacological: LMWH, UFH, fondaparinux, dabigatran, rivaroxaban, warfarin
what is the difference between UFH and LMWH?
UFH binds to plasma proteins so requires monitoring whereas nearly 100% bioavailability means no monitoring required
UFH requires continous IV infusion or twice daily sc administration, LMWH requires once daily dosing
UFH carries greater risk of osteoporosis and HIT
UFH can be reversed by d/c infusion so used when there is a high risk of bleeding whereas LMWH cannot be reversed
LMWH has reliable dose dependent anti coagulation effect
UFH has molecular weight from 3000 to 30,000D whilst LMWH is produced by enzymatic or chemical depolymerisation of UFH with a mean MW of 5000- reduced chain length so reduced capacity to inhibit thrombin
how is UFH monitored?
activated partial thromboplastin time (APTT)
what are the two types of heparin and how do they. work?
unfractionated
low molecular weight
sulphated glycosaminoglycan, biological product derived from porcine intestine
binds to unique pentasaccharide on antithrombin and potentiates its inhibitory action towards factor Xa and thrombin
what are the two steps of anticoagulant therapy?
rapid initial anticoagulation to reduce risk of thrombus extension and fatal pulmonary embolism
- parenteral anticoagulant: heparin, LMWH, fondaparinux, DOAC
extended therapy: orally active anticoagulant: vitamin K antagonist (warfarin), OR DOAC to prevent recurrent thrombosis and chronic complications such as post-phlebitic syndrome
how are DOACS used in management of VTE?
dabigatran, rivaroxaban, edoxaban, apixaban licensed in UK for treatment of acute DVT
enables rapid initial anticoagulation orally
continue maintenance dose for 6 months or longer for secondary prevention of VTE
apixaban and rivaroxaban dont need overlap with heparin- big advantage in outpatient setting
what is the traditional management of VTE using heparins?
give LMWH or UFH for minimum of 5 days if uncomplicated thrombosis or 7 days or longer if extensive disease
start warfarin therapy on day 1
overlap with LMWH or UFH until IKR is 2 for 2 days
what are the clinical features of lower limb DVT?
pain, swelling, increased temperature of limb, dilation of superficial veins
usually unilateral
what is the Well’s pre-test probability score?
clinical likelihood of DVT
stratifies patients into low, intermediate or high probability categories
what are the diagnostic tests for DVT?
venous ultrasonography: most useful objective test: non-compressibility of common femoral vein or popliteal vein diagnostic of DVT
contrast venography: reference standard for diagnosis of DVT
what are the clinical features of pulmonary embolism?
collapse, faintness, crushing central chest pain
pleuritic chest pain
difficulty breathing
haemoptysis
exertional dyspnoea
