A decade of The Glycocalyx Model paradigm.

Original Starling principle paradigmExtended Starling principle or Glycocalyx Model paradigm.
Intravascular volume consists of plasma and cellular elements.Intravascular volume consists of glycocalyx volume, plasma volume, and cellular elements.
Capillaries separate plasma with high protein concentration from interstitial fluid (ISF) with low protein concentration. Sinusoidal tissues (marrow, spleen, and liver) have discontinuous capillaries and their interstitial fluid (ISF) is essentially part of the plasma volume.
Open fenestrated capillaries produce the renal glomerular filtrate. 
Diaphragm fenestrated capillaries in specialized tissues can sustain absorbtion of ISF to plasma. 
Continuous capillaries exhibit ‘no absorption’.
The endothelial glycocalyx is semi-permeable to proteins and their concentration in the intercellular clefts below the glycocalyx is low.
The important Starling forces are the transendothelial pressure difference and the plasma–interstitial colloid osmotic pressure difference operating across a porous endothelial barrier. The important Starling forces are the transendothelial pressure difference and the plasma – subglycocalyx colloid osmotic pressure difference operating across the continuous glycocalyx.
Fluid is filtered from the arterial end of capillaries and absorbed from the venular end, while small proportion returns to the circulation as lymph.Transendothelial solvent filtration (Jv) is much less than predicted by Starling’s principle, and the major route for return to the circulation is as lymph.
Raising plasma colloid osmotic pressure with hyper osmotic colloid solutions enhances absorption and shifts oedema fluid from ISF to plasma. Raising plasma colloid osmotic pressure reduces Jv but does not cause sustained absorption of ISF and is not a sufficient treatment of oedema.
Auto transfusion after abrupt disequilibrium is a transient phenomenon, and limited to about 500 ml.
At subnormal capillary pressure, net absorption increases plasma volume. At subnormal capillary pressure, Jv approaches zero. 
Auto transfusion after abrupt disequilibrium is a transient phenomenon, and limited to about 500 ml.
At supranormal capillary pressure, net filtration increases ISF volume.At supranormal capillary pressure, when the colloid osmotic pressure difference is maximal, Jv is proportional to transendothelial pressure difference 
Infused colloid solution is distributed through the plasma volume, and infused isotonic salt solution through the extracellular volume. 100 ml of isosmotic colloid is equivalent to 400 ml of crystalloid for its contribution to plasma volume.Infused colloid solution is initially distributed through the plasma volume, and infused isotonic salt solution through the intravascular volume. The effect on plasma volume is context-sensitive.
At supranormal capillary pressure, infusion of colloid solution preserves plasma colloid osmotic pressure, raises capillary pressure, and increases Jv.
Infusion of isotonic salt solution also raises capillary pressure, but it lowers colloid osmotic pressure and so increases Jv more than the same colloid solution volume.
At subnormal capillary pressure, infusion of colloid solution increases plasma volume and infusion of isotonic salt solution increases intravascular volume, but Jv remains close to zero in both cases. 100 ml of isosmotic colloid is equivalent to no more than 150 ml of crystalloid for its contribution to plasma volume.
Traditional versus extended Starling principle paradigms for fluid therapy.

A Quick Summary of the new clinical teaching, based upon Charles Michel’s Extended Starling Principle.

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