What's Old, What's new?

Introduction
The diagnosis and treatment of DVT has undergone considerable change yet it remains a significant clinical problem.

Risk factors
These are well known (see Table I).
 

Laboratory: The D-Dimer blood test can be a very useful screen. Sarker et al showed that a value >250ng/ml was associated with a sensitivity of 100% and specificity of 38%.

Radiological: The duplex ultrasound is the diagnostic method of choice to confirm diagnosis. It should be used in those patients with low clinical probability but who have a positive D-Dimer and in those with high clinical probability of DVT. Phlebography may be used if the duplex investigation is problematic.

Management:

Prophylaxis: The main elements are heparin and compression stocking or pneumatic pumps. These can reduce perioperative DVT from 27% to 11%. Low molecular weight (LMW) heparin is favoured over unfractionated heparin because of its longer half life and lower risk of bleeding.

For long haul flight passengers it had been shown that compression stockings reduce the chance of DVT from 4.5% (in new users) to 0.24%. For high risk patients (previous DVT/genetic thrombotic problems) LMW heparin has been shown to significantly reduce the chance of DVT. It can be administered 2 to 4 hours before a flight.

Treatment: For most established DVTs, the best regime of treatment is once daily LMW heparin. This gives as god, if not better results than unfractionated heparin. This should be done in conjunction with compression and early ambulation. The latter two measures impede thrombosis extension more effectively than bed rest. This means most DVTs can be treated on an outpatient basis. Oral anticoagulants should be given for 3 months for the first DVT and for 6-12 months for recurrent DVT and pulmonary embolisms.

Thrombolysis: Catheter directed thrombolysis allows reduced doses of thrombolic agent to be used, to achieve more rapid dissolution of the clot. This can reduce the incidence of chronic venous insufficiency from 41% (with anticoagulation only) to 11%. It does carry the risk of bleeding (stroke 2-3%; other sites 15%). Its main role is probably in the young, fit patient with severe DVT (especially the phlegmasia syndromes) who can suffer considerable morbidity for the rest of their life due to the effects of chronic venous insufficiency (swelling and venous ulceration).

Thrombectomy: Surgical removal of the clot has largely lost favour as it is associated with a high incidence of re-thrombosis.

Caval Filters: These should be reserved for those with ilio-femoral DVTs who cannot tolerate anticoagulation or who get a pulmonary embolus despite anticoagulation.

Genetic thrombophilias
These should be suspected with a positive family history, DVT before 45 years or recurrent foetal loss.

Hormone therapy (oral contraceptives / HRT)
Oral contraceptives (OC) increase the risk of DVT 4-6 fold, the highest risk occurring in the third generation OC. This is increased further if a genetic thrombophilia is present. HRT increases the relative risk of DVT by 2 fold. It may seem that OC are a greater risk than HRT, but since HRT is usually given to patients over the age of 40, whose baseline risk of DVT is much higher, the problem is magnified.

Economy class syndrome
The press would have us believe that the case for long haul flights, causing DVT, is made. This is not so, although evidence is mounting. Scurr et al showed a 10% incidence of calf DVT following long haul flights. This study has been criticised for its exclusions. It would imply that 40 passengers on every Boeing 747 long haul flight develops a DVT - clearly too high. In a study of 61 cases of sudden death of passengers arriving at Heathrow Airport, 18% died of pulmonary embolisrn as opposed to only 3.5% of those waiting to depart. The LONFLIT I study showed no DVTs in 355 low risk passengers and a 4.9% incidence of DVT in 389 high risk passengers following long haul flights. Other studies have shown no increased risk of DVT. Clearly the risk of DVT during flying has been exaggerated, but circumstantial evidence suggests a link.

Diagnosis:

Clinical: The clinical features - swelling, tenderness and warmth will be recognised in less than 50% of cases with calf DVT and in about 80-90% of patients with ilio-femoral DVT. The severe forms - phlegmasia cerulea (blue leg) and alba (white leg) dolens should he recognised, as more aggressive therapy may be appropriate.