Why There is Severe Edema in Nephrotic Syndrome

Typical clinical symptoms of nephrotic syndrome are three highs and one low---massive proteinuria (≧3.5g/d), severe edema, hyperlipidemia, hypoalbuminemia (≦30g/L). In serious cases there will be serous cavity effusion and anuria.

Varying degrees’ edema is often the first symptoms of nephrotic syndrome and it usually starts from the eyelid and face and then gradually affect the limbs and then the whole body. There will also be serous cavity effusion such as pleural effusion and ascites and boys often have obvious scrotal edema. Serious cases will have stretch marks or purple marks in the skin. The weight can increase by 30% to 50% and edema is often accompanied by reduction of urine output. However the severity of edema has nothing to do with the prognosis.

What are the causes of edema in nephrotic syndrome:

1. Decreased plasma colloid osmotic pressure. The exchange of body fluid in and outside the blood vessels is regulated by the osmotic pressures in the two sides. Osmotic pressure include crystal osmotic pressure and colloid osmotic pressure. The former is determined by crystal materials (mainly the electrolyte) and has less influence on fluid exchange since the crystal materials can pass through the capillary wall freely. The latter is mainly determined by protein and is the major factor affecting fluid exchange sice the protein can not pass through capillary wall freely. In case of nephrotic syndrome, large amount of plasma protein is lost in urine and cause hypoalbuminemia and this will lower the plasma colloid osmotic pressure. When it is lowered to 0.8-1.1kPa from the normal value (3.3-4kPa), the fluid in the blood vessels will flow to the hypertonic tissues and cause edema.

2. The reduction of effective blood volume. The flowing out of fluids in the blood vessels will cause reduction of the effective blood volume and cause a series of changes in the body. The capacity receptor will stimulate the increase of antidiuretic hormone (ADH) and the renal tubules will absorb more water. Through activating the renin-angiotensin-aldosterone system, there will be secondary aldosteronism and cause increase of sodium re-absorption and decrease of sodium excretion. Retention of water and sodium will further worsen the edema.

The above two factors are the main reasons causing edema in nephrotic syndrome.