4.4 Venous Thrombosis Flashcards
VENOUS THROMBOEMBOLISM (VTE) Deep vein thrombosis (DVT) is common and can be associated with thromboembolism leading to a pulmonary embolism (PE):
• Risk of DVT and PE increases with age (less than 1 in 1000000 chance to occur in children under 20; 1 in 1000 chance in a 40-year-old adult)
• PE is a common cause of death in hospitals (present in 13% of hospital deaths; directly causes 5 – 10%) which is preventable via thromboprophylaxis
• Venous thrombosis may also be an indicator of underlying disease
- Mortality of VTE is 5%
- Recurrence 20% in the first 2 years and 4% per annum thereafter
- Post-thrombotic syndrome (PTS); __________________ (severe PTS in 23% of patients at 2 years; reduced to 11% for patients with compression stockings)
- Pulmonary hypertension; Rare (<3% at 2 years) but devastating with high mortality
Recurrent pain, swelling, ulcers
There are 3 contributory factors to thrombosis which makes up Virchow’s triad:
- Constituents of the blood (hypercoagulability)
- Vessel wall (injury to vessel wall or endothelium)
- Pattern of flow (stasis)
HYPERCOAGULABILITY
Hypercoagulability is determined by viscosity, platelet count and coagulation system:
Viscosity (determined by cellular or protein components)
- Increased ____________ : polycythaemia
- Increased protein/paraprotein: ________
Platelet count
- Increased platelet count: essential ___________
Coagulation system
- Increased procoagulant factors: raised factor VIII
- Decreased anticoagulant factors: ______
- Decreased fibrinolysis: pregnancy
haematocrit;
myeloma;
thrombocythaemia;
thrombophilia
Patients with deficiency in protein C/S or antithrombin would be predisposed to thrombosis:
• Often have a family history of thrombosis (2x risk of thrombosis)
Thrombophilic traits include inherited or acquired traits:
- Protein C/S or antithrombin deficiency: Often have a family history of thrombosis (2x risk of thrombosis)
- Factor V Leiden: Most common inherited abnormality (5% of Northern European populations), which is a polymorphic variant resistant to _____________ (factor V is extra sticky)
- ______________: Acquired isolated autoimmune phenomenon or part of an autoimmune condition (e.g. SLE)
Normal haemostasis is a balance between coagulation factors (driving fibrin formation) and anticoagulant factors (preventing fibrin formation):
• If the equilibrium is disturbed, the patient is either predisposed to thrombosis or bleeding
Lupus anticoagulant ;
protein C
VESSEL WALL: The vessel wall is normally antithrombotic as it is lined with _______________, and secretes ____________ (inhibits platelet aggregation):
• Part of the anticoagulant pathway is linked to the endothelium, so the endothelium expresses thrombomodulin (alters specificity of thrombin in favour of _______________)
• Endothelium also expresses tissue factor pathway inhibitor (TFPI)
Inflammation or injury of any type makes the vessel wall prothrombotic (e.g. infections, malignancies, vasculitis, trauma) via:
• Anticoagulant molecules are downregulated
• Adhesion molecules are upregulated
• Tissue factor increases in expression
• Prostacyclin production is decreased
*The incidence of VTE is most marked in __________________ (almost 15%).
naturally occurring heparin-like substances (heparans);
prostacyclin;
protein C;
pancreatic cancer
Stasis promotes thrombosis (high incidence of thrombosis in immobile patients; beneficial effects of compression stockings):
• Reduced removal of ______________
• Promotes platelet adhesion to the vessel wall
• Promotes leukocyte adhesion and transmigration (releasing cytokines to activate coagulation further)
Factors affecting flow
- Immobility : Surgery, paraparesis, travel
- Compression: Tumour, pregnancy
- Viscosity: Polycythaemia, ____________
- Congenital: Vascular abnormalities
activated coagulation factors;
Paraproteins
There is a _______________ between the flight distance and incidence of PE (longer flight distance has higher risk of PE the minute the passenger arrives):
• As time after travel increases (right graph), number of thrombosis cases also decreases in a dose-response effect
dose-response effect
In the 12 months after an idiopathic thrombosis, approximately 10% of patients will be diagnosed with cancer (with poor prognosis):
• _______________ in the UK is the most up-to-date guidance on what screening tests should be done for such patients
• If a patient is not already known to have cancer, the doctor should perform a _____________________
• Further investigations for cancer like
abdominopelvic CT scan (and mammogram for women) in all patients aged over 40 with first unprovoked DVT/PE who do not have signs or symptoms of cancer (based on initial investigations)
NICE clinical guideline 144;
physical examination, chest X-ray, blood tests (FBC, serum calcium, LFTs) and urinalysis
About 25000 people die from hospital-acquired thrombosis in England per year (20x more than the combined deaths from breast cancer, AIDS and traffic accidents):
• Intervention is cheap and effective via routine thromboprophylaxis (LMWH heparin)
• Avoiding hospital thrombosis involves a 5-step process which starts from admission:
o Assess ____________ → VTE risk assessment → bleeding risk assessment → consider _________________ → consider use of mechanical prophylaxis (e.g. compression stockings)
o Assessment is repeated at 24 hours or anytime the patient changes clinical status
VTE risk factors
- Active cancer
- Age > 60
- _____________, personal history or 1st degree relative
- Obese
- Varicose veins or ______________
- Dehydration
- Critical care
- Cardiac, metabolic, endocrine, respiratory, infectious, or inflammatory conditions
- Hormone replacement therapy or oral contraceptive pills
Bleeding risk factors
- Acquired or inherited bleeding disorders
- Active bleeding
- Anticoagulated
- Acute stroke
- Low platelets < 75
- High BP > ___________
- __________________within previous 4 hours or expected within the next 12 hours
- Medical patients are given LMWH or mechanical prophylaxis, while surgical patients are given LMWH and mechanical prophylaxis.
patient mobility;
pharmacoprophylaxis;
Thrombophilia;
phlebitis;
230/120
Lumbar puncture, epidural or spinal anaesthetic
Stockings need to be measured and must be removed daily to inspect the skin condition:
• Prescribed on the drug chart and should include graduated compression stockings, calf pressure of ___________________ , single/pair and lower limb/whole leg
• Contraindicated in the following groups of patients:
o ______________ (check pulses, inspect limb)
o Stroke
o Peripheral neuropathy or sensory impairment
o Peripheral arterial bypass grafts
o _________________ (causes of severe leg oedema)
o Unusual or deformed limb
o Delicate skin/dermatitis/gangrene/skin grafts
14 – 15mmHg;
Arterial disease;
Congestive cardiac failure
COMBINED THROMBOTIC RISK
Thrombosis is a multi-causal condition arising from interacting genetic and acquired factors:
• Difficult to predict how potential risk factors interact with each other (e.g. oral contraceptive pill increases risk by __________, factor V Leiden increases risk by ____________ → combined risk is ________–)
2 – 3x;
3 – 5x;
30x
