VENOUS THROMBOEMBOLISM

VENOUS THROMBOEMBOLISM. 

Venous thromboembolism (VTE) is an important condition within surgery, and autopsy studies suggest that it is the most common direct cause of death in surgical patients. Venous thrombosis is the formation of a semisolid coagulum within the venous system and may occur in the superficial system (usually described as superficial thrombophlebitis) or the deep system (deep venous thrombosis, DVT). Venous thrombosis of the deep veins of the leg may be complicated by the immediate risk of pulmonary embolus and sudden death. Subsequently, patients are at risk of developing PTS and venous ulceration. While DVT may occur in the upper limb, it is the leg that gives rise to the vast majority of the morbidity and subsequent complications of this condition.

Aetiology The three factors described by Virchow over a century ago are still relevant in the development of venous thrombosis. These are: 

● contact of blood with an abnormal surface (e.g. endothelial damage); 

● abnormal flow (e.g. stasis); 

● abnormal blood (e.g. thrombophilia).

Risk factors for venous thromboembolism. 

Diagnosis. 

The most common presentation of a DVT is pain and swelling, especially in the calf, usually in one leg; however, bilateral DVTs are common, occurring in up to 30%. When the swelling is bilateral, DVT must be differentiated from other causes of systemic oedema, such as hypoproteinaemia, renal failure and heart failure. Some patients have no symptoms of thrombosis and may first present with signs of a pulmonary embolus, e.g. pleuritic chest pain, haemoptysis and shortness of breath. Patients may also develop shortness of breath from chronic pulmonary hypertension. Sometimes the leg appears cellulitic and very occasionally it may be white or cyanosed: phlegmasia alba dolens and phlegmasia cerulea dolens. This indicates venous pressures that are so high that they are impeding tissue perfusion. Patients who present with venous gangrene often have an underlying neoplasm. Clinical examination for DVT is unreliable. Physical signs may also be absent. Mild pitting oedema of the ankle, dilated surface veins, a stiff calf and tenderness over the course of the deep veins should be sought. Leg pain occurs in about 50% of patients with DVT but is nonspecific. Homans’ sign – resistance (not pain) of the calf muscles to forcible

dorsiflexion – is not specific and should not be elicited. Tenderness occurs in 75% of patients but is also found in 50% of patients without objectively confirmed DVT. The pain and tenderness associated with DVT does not usually correlate with the size, location or extent of the thrombus. Clinical signs and symptoms of pulmonary embolus occur in about 10% of patients with confirmed DVT. A low-grade pyrexia may be present, especially in a patient who is having repeated pulmonary embolus. Patients may have signs of cyanosis, dyspnoea, raised neck veins, a f ixed split second heart sound and a pleural rub if they have pulmonary emboli causing right heart strain, although these signs may be subtle or absent.

Modified Wells criteria for predicting deep vein thrombosis (DVT)

Treatment

Treatment Deep vein thrombosis The management of DVT has in the past been focused upon reducing the risk of pulmonary embolus. Patients who are confirmed to have a DVT on duplex imaging should be  rapidly anticoagulated with a ‘treatment dose’ of subcutaneous LMWH. Patients with significant renal impairment should be commenced on intravenous unfractionated heparin. Patients who have a sensitivity towards heparinoids, such as those with heparin-induced thrombocytopenia, should commence on another anticoagulant, such as fondaparinux (an indirect factor Xa inhibitor) or bivalirudin (a direct thrombin inhibitor). This will achieve rapid anticoagulation and reduce the risk of embolisation. Typically, patients will then commence on warfarin for at least 3 months (or longer depending upon the persistence of risk factors or in recurrent cases). Patients who cannot be safely anticoagulated (usually due to bleeding risks) should be considered for a temporary inferior vena cava filter, until either they are safe to be anticoagulated or the risk of embolisation has subsided and the filter may be retrieved. Patients with active cancer typically remain on a LMWH. There is a range of newer or ‘novel’ anticoagulants (NOACs). These oral agents either directly inhibit factor Xa (rivaroxaban and apixaban) or thrombin (dabigatran). Work is ongoing to explore their place within patient management. Alongside the risk of pulmonary embolus is the risk to the patient’s leg. Two-thirds of patients will have developed a PTS within 5 years of their DVT. A PTS limb may present with any of the symptoms, signs and complications of venous hypertension discussed earlier, but are typically towards the most severe end of the spectrum and patients face a considerable deficit in their quality of life. A small number of centres are performing procedures aiming to treat this and these include venous recanalisation and stenting and sometimes venous bypass procedures. These procedures can be very challenging and although good results are possible, many patients are condemned to lifelong compression with unaddressed symptoms and complications. As the treatment of PTS is so challenging, attention is being turned towards prevention with the use of thrombolysis, endovenous thrombectomy and stenting. During thrombolysis, an agent such as tissue plasminogen activator is administered directly into the thrombus, either via the popliteal vein or by direct puncture in the groin. New devices are being marketed that physically disrupt the thrombus at the same time as local lysis is carried out. Some thrombi can be compressed by stent grafting, allowing the venous lumen to be opened, especially in the iliac region. A meta-analysis of randomised trials has shown that these treatments result in a significant reduction in PTS at 5 years (from 67% to 39%) but at a cost of an increased risk of significant bleeding complications (from 4% to 10%). Patient selection is important. Despite such promising data, access to these treatments remains limited.

Question (MCQ) 

A 35 year old female who is bed ridden for a last 7 days because of fracture of shaft of right femur, now complains of severe pain in left calf. She is also taking oral contraceptive pills. Keeping in mind the symptoms and risk factors mentioned, what is probable diagnosis?

A) Deep venous thrombosis

B) Drug reaction

C) Arterial thrombosis

D) Cellulitis

E) Lymphangitis

Correct: A (Deep venous thrombosis)

The most important factor predisposing to deep venous thrombosis is hospital admission for the treatment of a medical or surgical condition. Injury, especially fractures of the lower limb and pelvis, pregnancy and the oral contraceptive pill are other well recognized predisposing factors.