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Nephrology – Generalized Edema
Whiteboard Animation Transcript
with Timothy Yau, MD and Michael Connor, MD
https://medskl.com/Module/Index/generalized-edema


Edema refers to soft tissue swelling that results from the expansion of interstitial fluid volume. Edema can be focal, as a result of a local process such as inflammation or thrombosis, but generalized edema is usually a result of underlying cardiac, kidney, or liver diseases. When edema becomes severe and widespread, it is termed anasarca.

The most common cause of edema is related to general retention of sodium and water, leading to expansion of plasma volume. This leads to an increased capillary hydrostatic pressure, which results in isotonic fluid leaking into the interstitial space.

There are several causes of this but the most common are renal disease (e.g. reduced kidney function, primary renal sodium retention) and heart disease (e.g. congestive heart failure).

Another etiology for edema formation is a decrease in oncotic forces due to hypoalbuminemia. This can be seen in states of albumin loss (e.g. nephrotic syndromes, GI protein malabsorption) or decreased albumin synthesis (e.g. cirrhosis).

The broad approach to treating edematous states is to restore normal intravascular volume. In states of volume overload, as seen in kidney and heart diseases, this usually involves the use of diuretics to enhance salt and water excretion.

In low cardiac output states, inotropes can be used as well to improve stroke volume and enhance delivery of blood to vital organs.

Diuretics can also be used in hypoalbuminemic states as a temporizing measure, but addressing the underlying etiology of the low albumin is paramount. The use of albumin supplementation in hypoalbuminemic edematous states is controversial and usually not used as first-line therapy.

Occasionally patients can present with total body overload and manifest with edema, yet have a decreased effective arterial volume and low blood pressure. These patients pose a particularly challenging scenario as diuresis can be difficult in the setting of systemic hypotension.