Cause of edema in Nephrotic Syndrome: sodium water retention >>>Hypoproteinemia.
Reference—
- Brenner and Rector’s Nephrology.
Edema is a major characteristic of nephrotic syndrome.
A) UNDERFILL MECHANISM OF SALT AND WATER RETENTION :
Hypoalbuminemia reduces the oncotic pressure within the capillaries, and this favors the net translocation of fluid into the interstitial spaces.
To the extent that this occurs, intravascular volume and blood pressure fall, and this triggers the sympathetic nervous system, activates the renin-angiotensin-aldosterone axis, elevates vasopressin levels, and modulates many other control systems that act together to promote net renal salt and water retention.
This pathogenic sequence has been termed the underfill mechanism of salt and water retention in nephrotic syndrome.
B ) OVERFILL MECHANISM.
However, edema formation in many, PERHAPS MOST, NEPHROTIC PATIENTS CANNOT BE FULLY EXPLAINED BY UNDERFILL MECHANISMS.
Although reduced intravascular oncotic pressures certainly exist in nephrotic patients, the net hydrostatic gradient for water movement across capillary beds is also influenced by the interstitial oncotic pressure, and this generally falls in parallel with reductions in plasma oncotic pressure.
Consequently, the net hydrostatic pressure gradient from the intravascular compartment to the interstitial space may not significantly increase. Edema formation under these conditions may be the consequence of a primary form of renal salt and water retention. This pathogenic sequence for edema formation is called the overfill mechanism. “”””
NOTE: Undoubtedly each of these mechanisms plays a role in various phases and forms of nephrotic syndrome. these mechanisms may evolve from one form to the other.