Edema (cont.)
How does venous insufficiency cause edema?
The veins in the legs are responsible for transporting blood up to the veins of the torso, where it is then returned to the heart. The veins of the legs have valves that prevent
the backward flow of blood within them. Venous insufficiency is incompetence of the veins that occurs because of dilation, or enlargement, of the veins and dysfunction of their valves. This happens, for example, in patients with
varicose veins. Venous insufficiency leads to a backup of blood and increased pressure in the veins, thereby resulting in edema of the legs and feet.
Edema of the legs also can occur with an episode of deep vein thrombophlebitis, which is a blood clot within an inflamed vein. In this situation, the clot in the deep vein blocks the return of blood, and consequently causes increased back-pressure in the leg veins.
Venous insufficiency is a problem that is localized to the legs, ankles, and feet. One leg may be more affected than the other (asymmetrical edema). In contrast, systemic diseases that are associated with fluid retention generally cause the same amount of edema in both legs, and can also cause edema and swelling elsewhere in the body. The response to therapy with diuretic drugs in patients with venous insufficiency tends to be unsatisfactory. This is because the continued pooling of fluid in the lower extremities makes it difficult for the diuretics to mobilize the edema fluid. Elevation of the legs periodically during the day and the use of compression stockings may alleviate the edema. Some patients require surgical treatment to relieve chronic edema that is caused by venous insufficiency.
Which diuretics are used to treat edema?
Edema can become a problem in systemic diseases of the heart, liver or kidneys. Diuretic therapy can be initiated, often alleviating the edema. The most potent diuretics are loop diuretics, so-called because they work in the portion of the kidney tubules referred to as the loop of Henle. The kidney tubules are small ducts that regulate salt and water balance, while transporting the
forming urine. Clinical loop diuretics available are:
The doses of these diuretics vary depending upon the clinical circumstances. These drugs can be given orally, although seriously ill patients in the hospital may receive them intravenously for more prompt or effective response. If one of the loop diuretics is not effective alone, it may be combined with an agent that works further down (more distally) in the tubule. These agents include the thiazide type diuretics, such as hydrochlorothiazide (HydroDIURIL), or a similar but more potent type of diuretic called metolazone (Zaroxolyn). When diuretics that work at different sites in the kidney are used together, the response often is greater than the combined responses to the individual diuretics (synergistic response).
Some diuretics frequently cause an excessive loss of potassium in the urine, leading to the depletion of body potassium. These drugs include the loop diuretics, the thiazide diuretics, and metolazone. Patients on these diuretics are commonly advised to take potassium supplements and/or to eat foods high in potassium. High potassium foods include certain fruits such as:
- bananas,
- orange juice,
- tomatoes, and
- potatoes.
Patients with impaired kidney function often do not require potassium supplements with diuretics because their damaged kidneys tend to retain potassium. In certain instances, the volume of urine induced by the diuretic can be improved by adding a potassium-sparing diuretic, one that does not cause depletion of potassium. These diuretics include spironolactone (Aldactone),
triamterene (Dyrenium, a component of
Dyazide), and
amiloride (Midamor). Adding one of these diuretics to the patient's diuretic regimen may preclude the need for potassium supplements. Another diuretic that can be used is
acetazolamide (Diamox), which counteracts the development of an increased concentration of bicarbonate (too much alkali) in the blood. Increased bicarbonate sometimes occurs in patients receiving other diuretics.
Next: Are diuretics used for other purposes? »
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