Porth's Essentials of Pathophysiology, 4e

440

Circulatory Function

U N I T 5

malaise, and an elevated white blood cell count and erythrocyte sedimentation rate are accompanying indi- cations of inflammation. There may be tenderness and pain along the vein. Swelling may vary from minimal to maximal. As many as 50% of persons with DVT are asymptomatic. The site of thrombus formation determines the loca- tion of the physical findings. The most common site is in the venous sinuses in the soleus muscle and poste- rior tibial and peroneal veins. Swelling in these cases involves the foot and ankle, although it may be slight or absent. Calf pain and tenderness are common. Femoral vein thrombosis produces pain and tenderness in the distal thigh and popliteal area. Thrombi in ileofemoral veins produce the most profound manifestations, with swelling, pain, and tenderness of the entire extremity. With DVT in the calf veins, active dorsiflexion produces calf pain (i.e., Homans’ sign). Diagnosis andTreatment The risk of pulmonary embolism emphasizes the need for early detection and treatment of DVT. 81 Several tests are useful for this purpose: ascending venography, ultrasonography (e.g., real time, B mode, duplex), and plasma d -dimer (a degradation product of fibrin) assess- ment 84 (see Chapter 23). Whenever possible, venous thrombosis should be prevented in preference to being treated. Early ambu- lation after childbirth and surgery is one measure that decreases the risk of thrombus formation. Exercising the legs and wearing support stockings improve venous flow. A further precautionary measure is to avoid assuming body positions that favor venous pooling. Antiembolism stockings of the proper fit and length should be used routinely in persons at risk for DVT. Another strategy used for immobile persons at risk for development of DVT is a sequential pneumatic com- pression device. This consists of a plastic sleeve that encircles the legs and provides alternating periods of compression on the lower extremity. When properly used, these devices enhance venous emptying to aug- ment flow and reduce stasis. The objectives of treatment of venous thrombosis are to prevent the formation of additional thrombi, prevent extension and embolization of existing thrombi, and minimize venous valve damage. 83,84 Anticoagulation therapy (i.e., warfarin and low–molecular-weight war- farin) is used to treat and prevent venous thrombosis (see Chapter 12). A 15- to 20-degree elevation of the legs prevents stasis. It is important that the entire lower extremity or extremities be carefully extended to avoid acute flexion of the knee or hip. Heat often is applied to the leg to relieve venospasm and to aid in the reso- lution of the inflammatory process. Bed rest usually is maintained until local tenderness and swelling have sub- sided. Gradual ambulation with elastic support is then permitted. Standing and sitting increase venous pressure and are to be avoided. Elastic support is needed for 3 to 6 months to permit recanalization and collateralization and to prevent venous insufficiency.

SUMMARY CONCEPTS

R E V I EW E X E R C I S E S 1. The Third Report of the NCEP Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults recommends that a person’s high density lipoprotein (HDL) should be above 40 mg/dL. A. Explain the role of HDL in prevention of atherosclerosis. 2. A 55-year-old man presents at the emergency department of his local hospital with complaints of excruciating, “ripping” pain in his upper back. He has a history of poorly controlled hypertension. His radial pulse and blood pressure, which on admission were 92 and 140/80 mm Hg, respectively, become unobtainable in both arms. A transesophageal echocardiogram reveals a dissection of the descending aorta. Aggressive blood pressure control is initiated with the goal of reducing the systolic pressure and pulsatile blood flow (pulse pressure). ■■ Veins are thin-walled, distensible vessels that collect blood from the tissues and return it to the heart.The venous system is a low-pressure system that relies on the pumping action of the skeletal muscles to move blood forward and the presence of venous valves to prevent retrograde flow. ■■ The storage function of the venous system renders it susceptible to venous insufficiency, stasis, and thrombus formation. Disorders of the venous system produce congestion of the affected tissues and predispose to clot formation because of stagnation of flow and activation of the clotting system. ■■ Varicose veins are dilated and tortuous veins that result from a sustained increase in pressure that causes the venous valves to become incompetent, allowing for reflux of blood and vein engorgement. ■■ Venous insufficiency, which is associated with stasis dermatitis and venous ulcers, reflects chronic venous stasis resulting from valvular incompetence. ■■ Thrombophlebitis refers to thrombus formation in a vein and the accompanying inflammatory response in the vessel wall as a result of conditions that obstruct or slow blood flow, increase the activity of the coagulation system, or cause vessel injury. Deep vein thrombosis may be a precursor to pulmonary embolism.