EDEMA

What is Edema?

Edema is an accumulation of fluids in the interstitial spaces of the body. The most obvious symptom of this condition is swelling which, as everyone knows, characterizes various pathologies.

A simple but objective diagnostic criterion is based on local compression of the swelling with a finger. If a dimple is formed, called "fovea", the examination has been successful and one can speak of pathological edema. The fovea is more evident if the maneuver is performed in correspondence with a bony prominence, such as the anterior margin of the tibia and the sacrum. If, on the other hand, the edema is the consequence of trauma or is caused by an accumulation of mucopolysaccharides (myxedema), typical of hypothyroidism, the tissues immediately return to their original position.

Causes

Edema can be linked to local causes (circulatory difficulties such as varicose veins in the legs, skin inflammation, etc.) or extend to the whole organism. Kwashiorkor, a disease caused by an extremely low protein intake, manifests itself, among other things, with the appearance of widespread edema. This aspect gives the abdomen a swollen appearance (ascites), particularly evident in malnourished children who populate developing countries.

Why do the legs swell?

From a physiological point of view, edema is the result of alterations in the capillary exchange.

Under normal conditions, the capillaries tend to filter at the level of the arterial extremity and to reabsorb at the level of the venous extremity. The blood, which circulates very slowly inside them, can thus release oxygen and useful substances towards the arterial extremity and become loaded with waste products towards the venous extremity. These passages are favored by a very thin pressure gradient, because it is influenced by numerous factors, such as venous pressure and the concentration of proteins in plasma and interstitial fluid.

When we stand for a long time, our feet swell. In fact, standing implies an increase in venous pressure (gravity hinders the return of blood from the lower limbs to the heart). Because of this pressure increase, the whole capillary tends to filter, both at the venous and arterial extremities, there is no reabsorption and this causes the accumulation of liquids (edema). The same applies if a vein is occluded by a thrombus (phlebitis): the blood cannot pass, the venous pressure increases, the capillary reabsorbs with difficulty, fluid accumulates in the interstitial space and edema is formed.

All this would occur much more often than when it actually happens, if it were not for the action of the lymphatic system, responsible for the reabsorption of the interstitial fluid present in excess. An inadequate lymphatic drainage can in turn be responsible for edema and swelling (for example for example due to parasites, the growth of tumors, the removal of lymph nodes or the growth of fibrous tissue following radiation therapy).

Arterial hypertension, on the other hand, does not cause edema, as it is regulated by the arterioles upstream of the capillary.

Another cause of edema is heart failure. If one ventricle fails to pump all the blood from the other, blood accumulates in the systemic or pulmonary circulation. Again, there will be an increase in venous pressure, filtration will overcome resorption and edema will appear. Kidney failure, on the other hand, causes edema because the kidneys are unable to perform an effective filtering action and there is a loss of protein in the blood.

Malnutrition, a highly hypoproteic diet or the dietary and metabolic changes induced by alcoholism, as seen for Kwashiorkor, decrease the concentration of proteins in the plasma. Since these proteins recall water generating a pressure, called colloidosmotic, the decrease of their plasma concentration reduces capillary reabsorption, causing edema. Liver failure (especially cirrhosis) also leads to the same pathological manifestation, as the liver is the main site of plasma protein synthesis.

Finally, edema is a typical consequence of inflammation, which can arise from agents of a physical nature (trauma, heat), chemical (acids, etc.) or biological (bacteria, viruses, etc.). Due to the injury and some modifications of the microcirculation induced by the inflammatory response, there is an increase in capillary permeability, with consequent accumulation of proteins in the interstitial fluids (present in the extracellular space, i.e. between the capillary and the cell). Similarly to what has been seen for malnutrition, there is a decrease in plasma colloid-osmotic pressure and an increase in filtration at the level of the capillaries. Once again the result is the appearance of edema.