Special Investigations Test Advantages Disadvantages Contrast “ Gold standard” Invasive Venography Sensitivity ~ 100% Requires specialized equipment Easily interpretable Rare, but serious side effects MRI Highly accurate Expensive Safe during pregnancy Not readily available Non-invasive CT Non-invasive Limited data Can diagnose pelvic DVT Concurrently exclude PE Ultrasonography Highly accurate Not accurate for calf or pelvic DVT Non-invasive Complete study is time consuming D-Dimer Rapid laboratory study Only used to rule-out DVT Can aide in exclusion of DVT
Standard (unfractionated) heparin (SH) produces its anticoagulant effect by potentiating the activity of antithrombin which inhibits the procoagulant enzymic activity of factors IIa, VIIa, IXa, Xa, and XIa.
Low-molecular weight heparin ( LMWH) augments antithrombin activity preferentially against factor Xa. LMWH does not prolong PTT( unlike SH), and injections need only be given once daily SC and no monitoring is required, many pts can be treated at home.
SH is reserved for treating pts with very severe, life-threatening TE e.g. major PE giving rise to hypoxia or hypotension.
Dose: loading dose of 5000 U i.v, followed by a continuous infusion of 20U/kg/hr initially. PTT done after 6 hr, and if satisfactory daily thereafter. The aim is to keep PTT 1.5-2.5 times the control time.
Half-life of heparin is 1 hr, and if pt bleeds, it is sufficient just to discontinue the infusion; however, if bleeding is severe , the excess can be neutralised with i.v protamine. Treatment with either SH or LMWH should continue for 6-8 days, and it is appropriate to start warfarin therapy at the same time as heparin, and heparin should be contiued until INR is >2.0 for 2 consecutive days.
It inhibits vit. K-dependent carboxylation of factors II, VII, IX and X in the liver.
Dose: loading 10 mg orally on the first day, and subsequent daily doses depending on the INR. If single DVT it is given for 3-6 mon, if two or more it should be continued for life. Bleeding is the most common side effect of warfarin: 0.5-1.0%/yr. If INR is above therapeutic level stop warfarin and give a small dose of vit.k e.g. 5 mg orally or 2 mg by slow i.v inj. If the pt bleeds, give vit. K ¹ 1-5 mg slowly i.v, and