This is a condition in which blood clots form spontaneously in the deep veins of the lower or upper limbs. The deep veins of the limbs serve to carry de-oxygenated blood back to the heart and lungs. Risk factors for DVT include long-periods of immobility, after major surgery involving the limbs, pelvis or abdomen, obesity, dehydration and major trauma to the limbs. Some patients may have a genetic pre-disposition to DVT as their blood lacks the proteins to prevent spontaneous clotting or have proteins that promote clotting. Some rarer causes of DVT involve abnormal blood vessel anatomy e.g May-Thurner syndrome or Paget-Schroetter Syndrome in which the draining veins of the limbs are compressed by either a neighbouring artery or by ribs in a tight space. Another risk factor is the presence of underlying cancer which can result in the blood being more prone to clotting (paraneoplastic syndrome). You may have read about the “economy class syndrome” in which patients develop DVT of the legs after a long-haul flight. This results from a combination of immobility during the flight, sitting in cramped positions and dehydration in a pressurized plane cabin.
Most cases of DVT are fortunately not life-threatening and can be treated with medication. These are usually those cases with DVT involving the below knee segment of the legs or the forearm of the upper limb. However, patients with DVT extending above knee or upper arm towards the heart may be in greater danger as the clots in the DVT can break off in pieces and travel into the heart and lungs (embolize) resulting in a serious condition known as Pulmonary Embolism. (PE). This condition is life-threatening as it prevents oxygen transfer to the venous blood and is associated with significant mortality.
Patients with DVT can present with a swollen and tender limb. In the legs, it may start in the calf and then extend towards the thigh and groin. In the upper limbs, it can start in the forearm and extend upwards.
Patients can also present with a fast heartbeat (tachycardia) and shortness of breath, either in isolation or related to the limb swelling. This is a worrying sign as it indicates the presence of Pulmonary Embolism.
To prevent DVT from “economy class syndrome”, keep well-hydrated by drinking lots of water during a long-haul flight. Avoid excessive alcohol consumption.. Also avoid long-periods of immobility by getting out of the seat and walking around every 2 hours.
For patients about to undergo limb, pelvic or abdominal surgery, consider using anti-coagulation (blood thinning) drugs during the period before and after surgery.
The use of tight compression stockings can also prevent the formation of DVT.
Diagnosis is based on a high index of suspicion with a positive risk factor history coupled with positive ultrasound scans showing the presence of clots in the deep veins. Other associated investigations include a CT scan of the pulmonary arteries and a ventilation-perfusion scan if there is a suspicion of PE.
Other investigations include a blood screen for pro-clotting factors and tumour markers if there is underlying suspicion of cancer.
All patients with DVT must be stated on blood thinning medication (anti-coagulation) unless there is a good reason to withhold it (e.g prone to bleeding in the gut or recent bleeding stroke in the brain). The objective of the anti-coagulation is to prevent more new blood clots from forming. The body usually helps in dissolving the existing vein blood clots over time, sometime up to 6 months. As such, all patients should be on the anti-coagulation medication for up to 6 months.
If the DVT is extensive (e.g extending up the thigh and into the pelvic veins), it is sometimes necessary to use a combination of mechanical devices and special drugs to dissolve the clots. This process, known as thrombolysis, is usually done if the DVT is less than 2 weeks old and can be done via small groin vein puntures. It is done especially in cases where there is a suspicion of the veins being compressed or narrowed by surrounding structures (May-thurner syndrome). The thrombolysis is to prevent long-term problems associated with DVT such as the Post-Thrombotic Syndrome (PTS) abd limb venous ulcers. Other additional procedures include the use of stents to keep the compressed veins open.
If there is evidence of severe PE, it may sometimes be needed to remove the blood clots in the lung through thrombolysis or open chest surgery.
Other adjunctive procedures to prevent clots that have broken off from reaching the lung veins include the insertion of metallic filters in the inferior vena cava (the largest vein in the abdomen, draining the legs) to trap loose clots.
For cases of upper limb DVT, in addition to clot thrombolysis, it may sometimes be necessary to remove the 1st rib to reduce the tightness and compression of the upper limb veins as it travels in the region around the shoulder.
Patients may also be required to wear compression stockings to help resolve the limb swelling.