Edema

Edema, (alternate spelling: oedema) formerly referred to as dropsy or hydropsy, is the swelling of the body's tissues due to excess interstitial fluid retention. Edema can occur locally, often affecting the extremities (peripheral edema), or generally, affecting the entire body (anasarca).

In the body, there are two main compartments between which fluid is exchanged: the intravascular and extravascular compartments. Intravascular compartments include the cardiac chambers and the vascular system itself, whereas the extravascular compartments include everywhere else. Fluid moves easily between these compartments, and the extent of this movement is determined primarily by the balance between hydrostatic and oncotic pressures.

Hydrostatic pressure refers to the pressure exerted by gravity on a fluid at equilibrium, and tends to cause fluid to filter out into the extravascular compartment. Oncotic pressure is a form of osmotic pressure in which proteins in the plasma pull fluid back into the intravascular compartment. Typically these pressures are balanced relatively equally, with a net filtration into the extravascular compartment of about 1% of the plasma. The lymphatic system then transports this extra fluid back into the intravascular compartment through the thoracic duct. Therefore, any change in the balance of these pressures that results in a net filtration greater than the lymphatic system can effectively transport can cause edema.

Symptoms of Edema

In addition to pronounced swelling, typically the overlying skin will have a stretched, shiny appearance. In cases of pitting edema, the skin over the affected area will retain a distinct dimple for 10 to 15 seconds after being depressed. In patients with peripheral edema, the swelling is often worst after extended periods of sitting or standing. Anasarca, or general edema, will present with swelling covering the entire body. Ascites refers specifically to fluid retention in the peritoneal cavity, and results in distinct swelling of the abdomen.

Etiology

An increase in hydrostatic pressure can occur as a result of heart failure, kidney failure, liver failure or venous obstruction. Decreased oncotic pressure occurs in patients with malnutrition resulting in an abnormally low level of blood proteins. In addition, any conditions affecting the permeability of vascular membranes, including inflammation or tissue trauma, can also cause more fluid to "leak" out of the intravascular compartment. When the body notices that this leaking is happening, the kidneys in turn retain more water and sodium to make up for the loss of fluid, causing more blood to circulate and more leakage to occur. Edema related specifically to the impairment of the lymphatic system in carrying away interstitial fluid is referred to as a lymphedema.

Risk Factors

Edema itself is not a disease, but a symptom. Less severe forms of edema can result from lifestyle and general health factors such as:

• Staying in one position (sitting, standing or supine) for too long
• Increased sodium intake
• Hormonal changes due to menstruation
• Pregnancy

Edema can also occur as a side effect of several different medications, including:

• Vasodilators
• Calcium channel blockers
• Estrogen-based medication
• Non-steroidal anti-inflammatory drugs (NSAIDs)
• Certain diabetes medications

However, edema can also be a sign of severe underlying medical conditions, such as:

• Congestive heart failure
• Cirrhosis
• Kidney disease
• Chronic venous insufficiency
• Chronic lung diseases (pulmonary edema only)
• A damaged lymphatic system

Complications

If left unchecked, peripheral and general edema can result in the overlying skin becoming stretched, developing infections or ulcerating. Also, decreased blood circulation can lead to blood clots in the deep veins of the body, also known as deep vein thrombosis.

Diagnostic Studies

• Ultrasound of heart, chest, peritoneum and extremities
• Blood tests and urine analysis to evaluate renal and liver function, as well as albumin levels
• X-rays including MRI, CT scan, lymphangiography

Treatments & Interventions for Edema

Depending on diagnosis, the following precautions may help minimize the risk of developing edema in at-risk patients and to minimize complications in patients already exhibiting symptoms:

• Reduce daily sodium intake.
• Avoid tight clothing and jewelry that could constrict the affected area
• Avoid extreme temperatures.
• Keep the affected limb above your heart when possible.
• Lymphatic massage to the affected area can help move excess fluid. Find a qualified lymphedema therapist to properly perform this procedure.
• During activity, monitor the affected limb for any change in size, shape, tissue, texture, soreness, heaviness, or firmness.
• Pay particular attention to the limb during air travel, as the decrease in pressure and extended time seated can exacerbate existing symptoms of edema. Consider wearing a compression garment for such travel, except if you have open wounds or poor circulation in the affected limb

Treating edema should always begin with diagnosing and treating the underlying cause. Depending on the cause, diuretics may be prescribed to increase water output from the kidneys and combining these with a low-sodium diet can help to decrease fluid retention. Other medications and treatments may be prescribed as well. Peripheral edema can also be treated by wearing prescribed compression stockings or garments, which apply more pressure to the affected area and can help force fluid to be reabsorbed into the intravascular compartment.

References

Cleveland Clinic. Edema. Cleveland Clinic. http://my.clevelandclinic.org/disorders/edema/hic_edema.aspx. Accessed April 25, 2018.
Cunha JP. Edema. MedicineNet.com. MedicineNet, Inc. http://www.medicinenet.com/edema/article.htm. Accessed April 25, 2018.
Klabunde RE. Tissue Edema and General Principles of Transcapillary Fluid Exchange. Cardiovascular Physiology Concepts. https://www.cvphysiology.com/Microcirculation/M010.htm. Updated July 11, 2011. Accessed April 25, 2018.
Mayo Foundation for Medical Education and Research. Edema. Mayo Clinic. http://www.mayoclinic.com/health/edema/DS01035. Published October 11, 2011. Accessed April 25, 2018.
MediLexicon International Ltd. What Is Edema? What Causes Edema? Medical News Today. http://www.medicalnewstoday.com/articles/159111.php. Published July 29, 2009. Accessed April 25, 2018.