DVT Flashcards
List some DDx for leg swelling?
Exudate (inflammation -> vasodilation and proteinaceous exudate)
- cellulitis
- septic arthritis
Transudate (disturbed hydrostatic or colloid osmotic pressure, low protein -> clearer)
- RHF
- liver cirrhosis
- nephrotic syndrome
- leg abscess -> obstructing venous outflow
Other: haematoma, Baker’s cyst rupture, lymphoedema
List some DDx for leg pain?
Venous: DVT, ulcer, leg wound
Muscular: muscle pain, compartment syndrome
Skeletal: fracture
Infectious: septic arthritis, osteomyelitis, cellulitis, wound infection
What is the Well’s score for probability calculation of DVT/PE?
- active cancer (+1)
- calf swelling >3cm (+1)
- swollen unilateral superficial veins (+1)
- unilateral pitting oedema (+1)
- previous DVT (+1)
- swelling of entire leg (+1)
- localised tenderness along deep venous system (+1)
- paralysis, paresis, recent cast immobilisation of LL (+1)
- Bedridden (>3 days) or major surgery (past 12 weeks) (+1)
- alternative diagnosis (-2)
Scoring:
Likely: >2 -> Ix doppler US
Unlikely: <2 (DVT prevalence 5%) -> iX D-dimer testing
What risk factors could effect Virchow’s triad?
Virchow’s triad:
- Endothelial injury: smoking, surgery
- Abnormal blood flow: dehydration, immobility, surgery
- Hypercoagulability: surgery, malignancy, pregnancy, thrombophilia, drugs (OCP, HRT)
How is a Duplex US used?
Duplex US procedure:
• Pass transducer over skin above BV
• Transducer sends and receives sound waves (amplified by microphone) -> sound waves bounce of solid objects (e.g. RBCs) -> movement of RBCs reflected as change in pitch of reflected sound waves
No blood flow -> no pitch change
• Reflected sound waves process though computer -> provide info about speed and direction of flow
Looking for:
- reduced blood flow in the deep venous system (DVT)
- echogenic band inside vein (thrombus)
- venous diameter (decreased in acute, increased in chronic)
- non-compressible venous segment (thrombus)
- absent colour flow (completely occlusive thrombus)
- lack of flow augmentation of calf squeeze (DVT)
What is an ABI and how does it work?
Ankle brachial index (ABI): a measure of the ratio of systolic blood pressure at the ankle to the blood pressure in the upper arm
- Inflate cuff proximal to artery and continue inflation until pulse in the artery ceases
- Deflate cuff slowly, when artery pulse is re-detected through the probe, that is SBP
- Dorsal pedis and posterior tibial in each foot (take the larger value)
- Left and right brachial arteries (take the larger value)
Results:
<0.9 = narrowing/blockage of arteries in legs (arterial disease)
>1.2 = abnormal vessel hardening/calcification from peripheral vascular disease
How would you manage a DVT?
Non-pharmacological:
o Encourage exercise
o Compression stockings
Pharmacological:
o LMWH (e.g. Enoxaparin 1.5mg/kg SC, daily)- potentiates ATIII to bind and inhibit Xa -> reduce clot formation -> reduce thrombosis
o Unfractionated heparin if pt high bleeding risk (easier to reverse)
o Bridge to Warfarin (INR 2-3)- inhibits epoxide reductase -> prevent activation of vit K dependent clotting factors (2, 7, 9, 10)
- Started same day as LMWH and continued indefinitely.
- Monitored with monthly blood tests (INR, extrinsic pathway)
o IVC filter if pt actively bleeding -> prevent PE
Describe the MAO of Warfarin?
Warfarin MA:
inhibits epoxide reductase
-> preventing activation of vit K dependent clotting factors (2, 7, 9, 10) and anticoag proteins C and S
Note: initial prothrombotic effect (couple days): anticoag factors proteins C and S destroyed first (shorter half lives)
-> need to bridge with unfractionated heparin or LMWH
Note: teratogenic
Reversal: Vit K (rapid reversal with FFP)
Monitor: PT and INR (extrinsic)
List some SE of Warfarin?
SE:
- bleeding
- teratogenic
- skin/tissue necrosis (small BV microthrombi in first few days of hypercoagulability)
- drug-drug interactions: other palsma protein-bound drugs may displace warfarin causing more free fraction -> bleeding (e.g. Sulphonamides, Sulphonyureas, NSAIDs)
Describe the MAO of unfractionated heparin and LMWH?
Heparin MA: lowers activity of thrombin and factor Xa
Unfractionated heparin MA: increases antithrombin III activation -> inhibits factors IIa, Xa and other proteases
- used in renal impairment
LMWH MA (e.g. Clexane, Enoxaparin): potentiated antithrombin III action -> inactivate factor Xa only - better bioavailability, x2 longer half life, subcut, no lab monitoring (APTT/intrinsic), reversal difficult
Heparin reversal: protamine sulfate (positively charged moleculer binds negatively charged heparin)
Compare the monitoring of warfarin and unfractionated heparin?
Warfarin: monitor INR monthly
- extrinsic path
- international normalised ratio (INR) expresses PT in standardised way
- INR = (prothrombin time patient/ prothrombin time observer) x ISI
- Results: INR 1 is normal, INR 2-3 therapeutic ratio (longer to clot)
UFH: APTT daily
- intrinsic path
List some SE of heparin Rx?
Common (>1%):
- haemorrhage
- bruising at injection site
- hyperkalaemia
- non-immune thrombocytopenia
Uncommon (<1%):
- elevated liver enzymes
- anaphylaxis
- heparin-induced thrombocytopenia (HIT): delayed thrombocytopenia to day 5, more common in UFH, (IgG antibodies complex with heparin-PF4 -> platelet activation and lysis -> contents trigger coag cascade -> thromboses), Rx cease heparin
LTM SE: alopecia, osteoporosis
Drug interactions: azole antifungals, HIV protease inhibitors
