Edema (Water Retention): Causes, Types

Brief overview

What is edema? Swelling caused by fluid stored in the tissue
How does edema develop? Due to excess pressure in the smallest blood or lymph vessels, causing fluid to leak into the surrounding tissue
Classification according to various criteria: e.g. generalized and regional oedema, perifocal oedema, special forms (such as lymphoedema, Quincke’s oedema)
Causes: Often harmless (e.g. prolonged standing or sitting, heat, pregnancy), but sometimes serious, e.g. heart, kidney or liver disease, circulatory disorders, venous insufficiency, thrombosis, allergies, inflammation
When to see a doctor? If the affected part of the body becomes unnaturally warm or cold and turns bluish or reddish in color; in case of other symptoms such as pain, fever, shortness of breath, clouding of consciousness; in case of sudden onset or rapid increase in edema
Examination: medical history (anamnesis), physical examination, blood test, ultrasound if necessary
Treatment: Treatment of the underlying disease, dehydration tablets (diuretics) if necessary
Prevention: If the cause is harmless, exercise, elevation of the legs and warm-cold alternating baths; sometimes a low-salt and dehydrating diet is helpful

Edema: Description

Impaired fluid balance

Our body consists mainly of fluid, which is distributed in the cells, the spaces between the cells (interstitium), the connective tissue and the subcutaneous tissue. Even our bones contain water. And the blood also consists mainly of water with many different types of cells floating in it.

Several liters of fluid pass from the smallest veins (capillaries) into the interstitium every day. From there, the larger proportion returns to the bloodstream, where veins transport it back to the heart. Around ten percent of the interstitial fluid, on the other hand, flows out via the lymph channels. If the pressure within the veins increases, more fluid is pressed into the surrounding tissue. This in turn reduces the pressure in the vessels.

Regulation of the water balance

Special pressure sensors (baroreceptors) in the carotid artery and in the aorta regularly measure the pressure in the circulation. If the values are too low, an increase in blood pressure is triggered: The arteries constrict and the heart pumps harder and faster. This mechanism allows the body to adjust the blood pressure in the short term.

Vicious circle of protein deficiency

Sometimes, however, this leads to a vicious circle. In some diseases, for example, important proteins are missing in the blood. They normally retain water in the vascular system. If they are missing, the fluid passes more easily into the tissue and, conversely, is no longer absorbed properly. This results in edema. However, this also results in a lack of water in the circulation, which the sensors quickly detect. As a result, the body excretes less water. However, because the proteins are still missing, the retained fluid quickly returns to the tissue – the oedema increases, while water continues to be missing from the bloodstream.

Classification of edema

Edema occurs when the flow of blood through the capillaries changes. A distinction is made depending on the cause:

Hydrostatic oedema: This occurs because the pressure within the vessels (hydrostatic pressure) is increased, so that more fluid is squeezed out into the surrounding tissue.
Colloid osmotic oedema: A lack of protein in the blood causes the colloid osmotic (oncotic) pressure to drop, resulting in increased fluid accumulation in the tissue and the development of oedema.
Inflammatory oedema: As a result of inflammatory processes, but also allergies or burns, the vessel walls become more permeable, so that more fluid escapes from the blood into the tissue.

However, edema can also be classified according to criteria other than its mechanism of formation. For example, there are categories according to the location of the swelling:

Generalized oedema occurs all over the body (e.g. hormonally induced water retention in women before menstruation as part of premenstrual syndrome),
Regionalized (regional) oedema only affects one region of the body (e.g. on a lower leg after a thrombosis).
Perifocal edema forms in healthy tissue around a focus of disease (in tumors, abscesses or radiation)
Intracellular edema develops in a cell and causes it to swell.
Extracellular edema is located in the space between cells.

Another classification criterion is the course of an edema:

Acute edema (e.g. acute cardiac insufficiency, kidney failure, inflammation, burns, thrombosis)
Chronic edema (e.g. liver cirrhosis, chronic venous insufficiency)

There are also special forms of oedema such as lymphoedema and Quincke’s oedema.

Lymphoedema

In lymphoedema (lymphoedema), lymph fluid builds up in the lymph vessels: the lymph is not drained properly and also leaks into the surrounding tissue, causing it to swell. Sometimes the reason for this is congenital – the lymphatic system has a malformation.

Detailed information on this particular form of edema can be found in the article Lymphedema.

Quincke’s oedema

Quincke’s oedema (angioedema) is an acute swelling of the dermis and subcutis or the mucous membrane with the underlying connective tissue layer (submucosa). It usually forms on the face, in the area of the eyelids and lips, on the mucous membranes of the throat, on the epiglottis and on the tongue.

Quincke’s edema is sometimes congenital. However, it can also be acquired. In this case, it usually occurs as part of an allergic reaction, such as allergic hives (urticaria). Angioedema also often hurts or burns.

Quincke’s oedema can be life-threatening if it affects the pharyngeal mucosa or the larynx and causes acute respiratory distress!

Edema: Causes

Edema also often occurs in pregnant women, especially in the last few weeks before giving birth. Hormonal changes in the water balance and the condition of the connective tissue as well as increased pressure on the large veins in the abdominal cavity and the resulting impaired drainage can lead to water retention in the tissue.

Oedema all over the body

However, there can also be more serious reasons behind edema. Generalized oedema can occur, for example, with

Heart disease: Swollen legs are often the result of cardiac insufficiency, particularly of the right heart (right heart failure).
Kidney diseases such as nephrotic syndrome, inflamed kidney corpuscles (glomerulonephritis), kidney weakness or even kidney failure can cause a protein deficiency or an imbalanced electrolyte balance with water retention in the legs.

Liver diseases: The liver usually produces too little protein and the colloid osmotic pressure in the vascular system falls. Water retention in the abdomen (ascites, ascites) often occurs with liver cancer or liver metastases, liver cirrhosis and liver weakness.
Adrenal diseases often lead to impaired production of the hormone aldosterone, which results in water retention in the abdomen and legs.
Malnutrition: A sign of a long period of starvation is the “hungry belly”, which is caused by a lack of protein.
Medication: Antidepressants, high blood pressure medication, glucocorticoids (“cortisone”) and anti-inflammatory drugs can also cause edema.

Edema in a specific region of the body

Regional edema is mainly caused by:

Lymphatic drainage disorders: The tissue fluid is transferred back into the venous vessels via the lymph channels. Congenital or mechanical disorders (external pressure, bruising) disrupt the lymphatic drainage and thus cause swelling in the tissue. Causes include tumors, operations and radiation. However, infestation with parasitic threadworms of filariasis can also cause an extreme form of edema, elephantiasis.

Circulatory disorders can affect veins or arteries and, in addition to edema, can also cause an undersupply of the tissue.
Chronic venous insufficiency (chronic venous insufficiency, CVI): Damaged venous valves in particular prevent the blood from flowing back to the heart properly. Instead, it builds up due to gravity, particularly in the legs. This can lead to severe water retention.
Inflammations, burns and injuries: This can make the vascular walls more permeable, which promotes water retention in the surrounding tissue.

Allergies: Contact with an allergy trigger (allergen) triggers immune cells, whose messenger substances make the vessel walls more permeable. As a result, more fluid leaks from the vessels into the tissue, causing swelling. This can also lead to Quincke’s oedema (see above).
Hereditary angioedema (HAE): This hereditary special form of Quincke’s oedema is characterized by acute and intermittent swelling, particularly in the extremities, but also in the abdominal organs. The occurrence of these swellings is unpredictable.

Edema: Examinations

Many edemas disappear on their own. This applies in particular to water retention after prolonged standing or sitting and to swelling of the eyelids as a result of an allergic reaction. In these cases, it is generally not necessary to see a doctor. However, there are situations in which you should definitely see a doctor.

Edema: When to see a doctor?

You should always consult a doctor if the following applies to you:

The edema has only developed on one side and quickly
The edema does not disappear on its own or becomes larger
The swelling is also warm, reddened or painful
The affected part of the body becomes unnaturally warm or cold and turns bluish or reddish in color
With fever
With shortness of breath
In case of clouding of consciousness up to delirium

Examinations by the doctor

The doctor will first ask you about your medical history (anamnesis). The following information is particularly important:

When did the edema develop?
How does it manifest itself (pain, spread, progression)?
What medication are you taking?
Do you suffer from any previous illnesses or allergies?
Do you also have shortness of breath?
Do you have to urinate frequently at night? (The reason: when lying down, the water from the edema flows more easily back to the heart, from where it is pumped to the kidneys and excreted)

The next step is a physical examination. The edema itself is usually easy to recognize. Its location gives the doctor the first clues in the search for the cause. For example, swollen legs are more likely to be found in cases of cardiac insufficiency, thrombosis or venous disease, while water retention in the abdomen (ascites) often indicates liver damage.

Blood tests show whether there is a protein deficiency or disorders of the blood salts. In addition, the urine can be examined for protein (proteinuria) – in kidney diseases, the body typically loses protein in the urine.

Sometimes imaging procedures are also used. Ascites, for example, can be detected using an ultrasound examination. This allows an assessment of how much water has accumulated in the abdominal cavity and whether the cause may be in the liver. The leg veins and possible thromboses can also be clearly visualized using ultrasound.

Edema: treatment

Edema treatment depends on the cause. In the case of venous insufficiency, for example, compression stockings help to combat the oedema. They are also used in the case of thrombosis as soon as the oedema has subsided (until then, a compression bandage is applied). Thrombosis patients also receive anticoagulant medication (anticoagulation).

Sometimes the doctor has to prescribe dehydrating medication (diuretics), for example in the case of heart or kidney-related edema. It is important to take the correct dosage of medication and to ensure an appropriate fluid intake. It is important to find a balance between fluid intake and excretion and to avoid losing important salts.

Loop diuretics such as furosemide or torasemide are effective, but also flush out salts such as potassium and sodium.
Potassium-sparing diuretics such as spironolactone are used in particular for ascites with liver damage or in patients with cardiac insufficiency.
Thiazide diuretics are often concomitant medications in antihypertensive therapies, but also disturb the blood salt balance (sodium (!), potassium, magnesium)

Edema: What you can do yourself

If it is normal, harmless water retention, you can gently remedy the situation yourself with a few tips. However, if you have a medical condition, such as heart or kidney disease, it is essential that you speak to your doctor before using these tips.

Exercise: Active leg muscles act as a “muscle pump” to ensure that water is transported back to the heart via the bloodstream.
Draining teas: Some plants are said to support the drainage of the body. Nettle tea or green tea are good examples. Tea made from St. John’s wort also has a dehydrating effect, but is not suitable for women who are taking the contraceptive pill.
Dehydrating foods: Some foods are also said to have a dehydrating effect. These include rice and potatoes in particular. Pineapple, strawberries, fennel and lettuce also expel fluid from the body.
Elevate your legs: Elevating your legs often helps against swollen legs.
Circulation-promoting measures: Kneipp baths with alternating warm and cold water keep blood vessels and muscles healthy. Blood circulation in the feet increases, the veins pump more blood back to the heart and the tendency to oedema decreases. You can read more about this in the article Hydrotherapy.

It remains important: If you keep getting edema or it doesn’t go away at all, talk to your doctor. This is the only way he or she can determine the cause and recommend suitable treatment for the edema.

Frequently asked questions

You can find the answers to the most frequently asked questions on the subject in our article Frequently asked questions about oedema.