Edema is the name given to localized swelling somewhere on the body. The best known is the edema that occurs in the legs. Edema though can occur at any place of the body. There are pulmonary edema, cerebral edema, laryngeal edema, tongue edema, etc.
Let us understand what edema is. The swelling of organs will be described another time. Now only visible swelling on the skin will be explained.
Contrary to what one might imagine, our blood vessels are not waterproof and have pores that allow the input and output of cells, bacteria, proteins and water.
The swelling occurs when there is excessive liquid outlet for a fabric. In fact, the excessive water flows to the interstitial space, the space between the tissue cells.
When inflammation occurs, the blood vessels become more permeable to facilitate the arrival of the defense cells to the site of infection or trauma. With the enlargement of pores, there is a greater fluid extravasation into the surrounding tissues.
The process of edema formation in a trauma or infection is easy to understand and is thoroughly explained in the link above. The problem is that the edema can form in several other situations. There are three mechanisms for the formation of edema in addition to increased permeability of vessels.
Increased pressure
Increased pressure within the veins and capillaries. This increase has nothing to do with hypertension, which is the elevation of blood pressure. It is worth remembering that the arteries carry the blood from the heart to organs and tissues while the veins the other way bring back blood from the tissues to the heart.
The increase in venous pressure occurs when there is some kind of obstruction, even partial, of the venous blood flow. We call it the increased hydrostatic pressure, i.e., when pressure of the liquid volume inside the vessel is on the wall itself.
Varicose veins
A known example is varicose veins in the legs. Varicose veins are veins that have defective difficulty in taking blood back to the heart. It is worth remarking that the veins of the legs must act against gravity, and when there is a defect in this system, there is a damming of blood in the lower limbs. The accumulated blood in the veins increases the pressure within them and causes fluid extravasation into the subcutaneous tissue. This situation is called venous insufficiency of the lower limbs.
Similar mechanism occurs in case of heart failure, where a weak heart cannot pump blood efficiently, again favoring the same situation in the lower limbs.
Both heart failure and venous insufficiency in the lower limb, edema appears and worsens when the patient stands for a long time and tends to disappear after a few hours in bed, when gravity does not exert opposing force.
One of the typical signs of swelling in the legs or locker is the Godet signal, which is the presence of a small sinking digital pressure to the skin. It is a sign of excessive fluid in the subcutaneous tissue.
In some diseases, especially of renal origin, there is an accumulation of sodium (salt) in the body. This excess of salt increases the amount of body water, which consequently increases not only the blood pressure but also the venous pressure, favoring the appearance of bumps.
The two mechanisms described above (vascular permeability and increased venous pressure) causes located edema, in the legs or the affected site of trauma or inflammation. In the case of salt retention, edema tends to be more diffuse.
Decreased blood viscosity
Another mechanism for the formation of lumps is decreased blood viscosity, called the oncotic pressure, and is mainly caused by the protein concentration in blood.
While the increase in pressure within the veins favors the leakage of liquids, the oncotic pressure acts the opposite way. Therefore, the formation of edema is a balance between the hydrostatic pressure and oncotic pressure.
When one has a condition which reduces the blood proteins (albumin is the major), the patient tends to form edema, even though the pressure within the veins is normal. In this case the swelling is widespread, since the lack of protein occurs throughout the body.
Ascites
When edema occurs in a diffuse way, we call it anasarca. The characteristic of this type of edema is cirrhosis. The main producer of albumin in the body is the liver. When it stops working properly, reduced protein synthesis occurs and consequently it leads to the oncotic pressure. The end result is the anasarca.
A type of swelling characteristic of cirrhosis, and that is part of anasarca, is ascites, which occurs by leakage of fluid into the abdominal cavity. It can also occur in advanced heart failure. Ascites has two mechanisms: caused both by the absence of albumin and by increased pressure in the veins of the liver common in cirrhosis.
Another disease that can cause diffuse edema and ascites is the nephrotic syndrome, which is nothing more than a kidney disease where there is loss of protein in the urine. In fact, any serious chronic disease may inhibit the production of albumin by the liver and cause edema.
Lymphedema
Lymphedema
Another type of edema, less common, is the origin of lymphatic. It is called lymphedema and occurs due to obstruction of lymphatic vessels. It occurs in elephantiasis, in cancers, in the morbidly obese and upper limbs of patients who do mastectomy and have their axillary lymph nodes removed. In venous insufficiency, severe and untreated, associated lymphedema can also occur.
Lymphedema is more crippling than the venous edema and can be quite asymmetric. The swelling is often caused by more than one mechanism.
There is a kind of swelling that occurs mainly in young and healthy people, normally associated with the menstrual period. It is also associated with obesity and depression. There is no apparent cause.
Edema is often cyclical and many women take diuretics before the menstrual period for symptom relief. In fact, taking a diuretic for this type of edema only worsens the situation. Chronic use of diuretics without giving a cause of edema is as paradoxical as it may seem.
The diuretic wrongly indicated increases sodium retention, especially in the intervals between shots. The patient ends up being dependent on medication and cannot establish a causal link with the diuretic. Indeed, the patient feels that only relieves its diuretic edema. When suspending the diuretic, there is a worsening of edema, which frightens and causes it to return the product. After a few weeks without a diuretic, edema subsides alone.
So healthy people should not use diuretics for small edemas in lower limbs, especially if associated with menstrual periods. It is best to reduce salt intake, stop taking drugs that may cause edema as nifedipine, amlodipine, anti-inflammatory rosiglitazone and minoxidil. Those who are overweight, weight loss is necessary.
A type of edema is common in clinical practice that occurs in a patient with long hospitalization, especially in the ICU.
