The circulatory system can be divided based on blood vessels types. The venous system comprises blood vessels which carry blood from tissue and organs allowing a return to the heart. The majority of veins carry deoxygenated blood with the exceptions of the umbilical vein which is patent during fetal development, growth and closes after birth and the pulmonary vein. The 3 layers which constitute the structure of a vein are the outer connective tissue layer (tunica adventitia or tunica externa); the middle smooth muscle layer (tunica media); and the inner endothelial cell layer (tunica intima). The middle, smooth muscle layer is less muscular in veins compared to arteries allowing for increased capacitance; however, valves are needed to provide unidirectional flow.
Venous obstruction is partial or complete occlusion of the lumen and can be related to decreased flow and increased pooling. The most commonly seen is a deep vein thrombosis in the lower extremities — venous stasis results in increased viscosity and the formation of microthrombi. This is due to any factor which slows or obstructs the flow of venous blood. One of the most common causes is endothelial (intimal) damage secondary to intrinsic or secondary to external trauma. In a hypercoagulable state, a biochemical imbalance between procoagulant and anticoagulant factors occur. Chronic venous insufficiency is a manifestation of decreased vein wall contractility and vein valve dysfunction.
Other areas affected by venous obstruction include portal vein obstruction which is primary thrombosis of the portal vein.
Venous thromboembolism (VTE) is a multifactorial disorder which can be due to inherited or acquired risk factors.
Each year, there are about 4,000,000 surgical patients and 8,000,000 medical patients who are hospitalized in the United States at moderate or high risk for VTE. In a global cross-sectional study, a large proportion of hospitalized patients were also at moderate or high risk for VTE, more specifically, 42% of medical patients and 64% of surgical patients. Among hospitalized medical patients, the 4 risk factors most predictive of VTE in the Intermountain Healthcare database were: (1) previous VTE, (2) bed rest, (3) peripherally inserted central venous catheter, and 4) cancer. Of particular importance is VTE in the outpatient setting. In a community study in Worcester, about three-fourths of patients developed VTE as outpatients. More than half had undergone surgery or had been hospitalized within the prior 3 months. Cancer, severe infection, or congestive heart failure increased the likelihood of a poor outcome from VTE in the community setting. In a population-based study in Norway, the incidence rate for all first VTE events was 1.43 per 1000 person-years. For DVT it was 0.93 per 1000 person-years with a 30-day case-fatality rate was 4.6% for DVT. Incidence rates increased exponentially with age and were slightly higher in women than men.
Venous thrombosis pathogenesis is based on the triad of Virchow proposed in 1865. The triad includes venous stasis, changes in the vessel wall, and/or changes in the blood leading to a hypercoagulability state which can increase the risk of obstruction.
Venous obstruction is most commonly seen in the form of deep venous thrombosis (DVT). Patients present with unilateral or bilateral leg swelling after prolonged stasis, for example, plane travel or another long period of inactivity. Other symptoms include leg pain, which can occur in 50% of patients and is aggravated by dorsiflexion. Edema, if present, is one of the most specific symptoms of DVT. There is no correlation to the pain and tenderness to the size of the thrombus.
Finding are usually confined to the affected limb. These include tenderness to the calf with a positive Homans sign which is a pain with passive dorsiflexion). Leg swelling of 2 centimeters or more in the affected limb is suggestive of DVT, and a positive D-dimer test shows the highest correlation to DVT.
Symptoms of portal vein thrombosis include right upper quadrant pain, nausea, and/or fever. Patients may have progressive ascites and ischemia of intestine due to microthrombi propagation of blood vessels. Intestinal suffusion secondary to acute portal hypertension can also be present.
Evaluation of DVT includes blood tests to help stratify patients with the risk for deep venous thrombosis (DVT) include D-dimer assay; levels of antithrombin III (ATIII), N-terminal pro-brain natriuretic peptide (NT-proBNP), and C-reactive protein (CRP); and erythrocyte sedimentation rate (ESR). Studies have shown all patient presenting with a positive D-dimer and leg swelling have confirmed DVT on evaluation.
Radiologic investigations include an ultrasound of the affected leg and pelvis. It may require additional evaluation in some patients with either CT (computed tomography) scan or MRI (magnetic resonance imaging).
Investigation for portal vein thrombosis includes laboratory test: coagulation studies to rule out inherited coagulation disorders, liver function test, and radiographic imaging. Ultrasound is the first line modality, and this can be done endoscopically. Further imaging modalities are MRI or MRA and possible CT scan.
Management of VTE is to prevent further extension of DVT proximally and the prevention of pulmonary embolism. Treatment is divided into an initial active treatment phase of 3 months and a subsequent secondary phase. Anticoagulation during the initial treatment shows a reduction in the risk of embolization in patients with proximal DVT or PE and reduces the risk of death in patients with PE.
Initial treatment consists of the administration of an anticoagulant. Anticoagulants include low molecular weight heparin (LMWH) or fondaparinux or unfractionated heparin (UFH) for a minimum of 5 days, with early administration of a vitamin-K antagonist (VKA) like warfarin. An international normalized ratio (INR) of at least 2 is achieved on 2 consecutive days, because of the slow onset of action of the antithrombotic effect of VKAs. After the first 3 months, management is based on the risk of bleeding compared to the risk of recurrent thrombosis. Thrombectomy of venous obstruction is less frequently performed, and often, an IVC filter is placed in patients in whom anticoagulation is contraindicated.
Treatment for portal venous obstruction includes thrombolysis using tissue-type plasminogen activator (tPA) through the transhepatic route, followed by prolonged anticoagulation therapy with warfarin for at least 3 months.
If treated appropriately, the overall prognosis of VTE is good.
The overall mortality has been reported to be less than 10% in chronic pulmonary vein thrombosis.
Complication of VTE is pulmonary embolism of the pulmonary artery which can lead to death.
Portal vein thrombosis complications include splenomegaly, esophageal- and gastric varices with or without bleeding, portal hypertensive gastropathy, and ascites.
Veins in almost any organ can be thrombosed or occluded. In many cases, because of collateral formation, symptoms do not occur immediately. However, the problem with vein thrombosis is the potential for the clot to embolize. Each year thousands of patients die from a pulmonary embolism, and in most cases, the cause is an embolic blood clot from the extremities. Healthcare workers including nurse practitioners must be aware of the complications of vein obstruction, particularly in the leg and pelvic veins, central neck veins, hepatic veins, and the superior mesenteric veins. In many cases, a duplex ultrasound will reveal the vein obstruction, and appropriate patient referral is necessary.
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