Preventing deep vein thrombosis

Dr Louise Johnson explains the dangers of deep vein thrombosis (DVT) and advocates prevention is better than cure.

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DVT is a blood clot in a vein, usually in the leg and is a type of peripheral venous disease (PVD).

The earliest known reference to PVD (the broad term referring to disorders affecting the blood vessels carrying blood to and from the arms and legs) is found on the Eber Papyrus, which dates from 1550 BC.

In more detail, DVT is the presence of coagulated blood, a thrombus, in one of the deep venous conduits that returns blood to the heart. DVT is defined as the development of a thrombus within the deep veins of the pelvis or lower limbs.

The prevalence of DVT is reported to be 100 per 100 000 people per year.¹ The incidence increase with age and the incidence is higher in men than in women.

Anatomy

The peripheral venous system functions both as a reservoir to hold extra blood and as a conduit to return blood from the periphery to the heart and lungs. Unlike arteries which possess three well-defined layers (a thin intima, a well-developed muscular media, and a fibrous adventitia), most veins are composed of a single tissue layer called endothelium. The lower limb deep venous system is typically thought of as two separate systems, one below the knee and one above.

Pathophysiology

In the 19^th century, Rudolf Virchow described three factors that are critically important in the development of DVT.

1. Venous stasis or sluggish blood flow
2. Activation of blood coagulation
3. Venous endothelial damage (vessel wall damage)

These factors have come to be known as the Virchow triad.

Risk factors

• Age – The incidence of DVT increases with age and is very rare in childhood.
• Orthopaedic surgery – DVT is more common in patients with lower limb fractures or after hip or knee replacement surgery.²
• Trauma – Incidence of DVT is significantly higher in patients with lower extremity fractures than those with trauma at other sites. The homeostasis of coagulation shifts to a pro-thrombotic state early after trauma injury. Thus, it is necessary to give anti coagulation medicine early on in treatment. Patients with trauma have a six-fold increase in DVT.
• Cancer
• Other factors, such as:
  • Immobility (flights or trips sitting longer than six hours)
  • Pregnancy and postpartum
  • Varicose veins
  • Heart attacks
  • Renal impairment
  • Long hospitalisation
  • Obesity
  • Hormonal therapy

Clinical manifestations

History

Patients will complain about local pain and swelling in a limb. Usually, it’s only on one side. Tenderness occurs in 75% of patients. Associated risk factors may be present.

Clinical picture

• Limb swelling
• Homans sign (Calf pain when the foot is flexed upwards. It is only seen in 50% of all DVT patients).
• The lower limb may have a red purple colour due to venous obstruction.
• A palpable, indurated, cordlike, tender subcutaneous venous segment.

Diagnosis

The American Academy of Family Physicians (AAFP) recommend a workup of patients with a probable DVT using the Wells scoring system. A Wells score of more than two has a high probability of a DVT.

Wells scoring system

Active cancer within six months +1

Immobilisation of lower limb in cast +1

Localised tenderness of venous system +1

Unilateral swelling of leg +1

Calf swelling more than 3cm circumferential increase+1

Previous DVT +1

Recent bedridden >3 days or major surgery +1

Alternative diagnosis at least as likely as DVT -2

Tests

D-dimer is a test that is easily performed by a blood sample. D- dimer is a small protein present in blood after a clot is degraded. Serum levels of D-dimer may increase in clinical conditions where clots form, for instance surgery, trauma, cancer, sepsis and haemorrhage, particularly in hospitalised patients. Interestingly, these conditions are also correlated with greater risk of DVT.³

The level of D-dimer remains increased in patients with DVT for approximately seven days. Patients that present late in the disease course may have a low level. Solitary DVT in the calf with a low clot burden may have a low D-dimer. Although D-dimer can’t verify DVT diagnosis, it may be highly useful to rule out DVT.

Venous ultrasound is the primary imaging modality to diagnose DVT. It’s safe, non-invasive, and cheap. The sensitivity of compression ultrasound in diagnosing DVT is 94% and its specificity is 98%.

Differential diagnosis

Other conditions that can cause similar symptoms as a DVT that should be considered are:

• Lymph node enlargement
• Superficial hematomas
• Femoral artery aneurism
• Baker’s cyst
• Superficial thrombophlebitis

Treatment

Left untreated, DVT can be complicated with pulmonary embolism (PE), which is a blockage in an artery of the lungs caused by a blood clot that has travelled from elsewhere in the body, at an early stage, and is associated with a high risk of recurrence.

Medical treatment

Low molecular weight heparin (LMWH) is recommended as an injection early in the diagnosis to stabilise the clot and prevent propagation of the clot and complications, such as pulmonary clots

Once intense anticoagulation is in place, the patient can be switched to either warfarin or to the newer drugs called non-vitamin K oral anticoagulants (NOACs). These drugs have less bleeding and is as effective as warfarin and need not be tested for dosing. Unfortunately, they are currently still expensive. There are three currently available in South Africa.

Other options

In patients with life-threatening clots, an inferior vena cava (IVC) filter can be inserted by a vascular surgeon.

In patients with massive iliofemoral thrombosis or limb-threatening thrombosis, thrombolysis (a procedure that breaks up blood clots using medication or a minimally invasive procedure) can be used. It has a risk of intracranial haemorrhage.

Prevention

The most important treatment of DVT is to always remember to take precautions to prevent it in the circumstances in which it may occur.

All patients admitted to hospital must be evaluated as a possible risk for a DVT.

Circumstances to consider

1. Choose anaesthesia well. Spinal or epidural anaesthesia can enhance blood flow and reduce DVT by approximately 50%.
2. Surgical technique. Meticulous operative skill with as little torsion of veins as possible to prevent endothelial vein damage. Choose surgeon wisely.
3. This should be adopted as soon as possible after operation. Walking improves the blood flow of the veins. Remember bedrest is exercise for the coffin.
4. Compression stockings. The below knee and above knee stockings have a similar effect if the stockings are well-fitted.
5. Intermittent pneumatic compression. This device also referred to as calf pumps can facilitate post-operative blood flow when patients are bedbound.
6. Chemical methods. Use either LMWH injections or a NOAC tablet as part of prevention.

Accurate and prompt diagnosis of DVT is necessary because thrombosis left untreated can cause life-threatening complications like PE. Remember, prevention is always better than cure in this instance.

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References

1. Al-Hameed F, Al-Dorzi HM et. al. “The Saudi clinical practice guideline for diagnosis of the first DVT of the lower extremity” Ann Thorac Med 2015;10 3-15
2. Whiting PS, White-Dzuro GA et. al. “Risk factors for DVT following orthopedic trauma surgery: an anlysis of 56000 patients.” Arch Trauma Res 2016;5 e32915
3. Adam SS, Key NS et. al.) “D-dimer antigen: current concepts and future prospects.” Blood 2009;113:2878-2887
4. Osman AA, Weina J et. al. “Deep venous thrombosis: a literature review” Int J Clin Med,2018;11(3):1551

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