The BJA Review that started it all;
Woodcock TE, Woodcock TM. Revised Starling equation and the glycocalyx model of transvascular fluid exchange: an improved paradigm for prescribing intravenous fluid therapy. Br J Anaesth. 2012;108:384-394.
FULL TEXT HTML or .pdf files are available from BJA
I summarise traditional teaching based on the Original Starling principle as follows;
◆ Intravascular volume consists of plasma and cellular elements.
◆ Capillaries separate plasma with high protein concentration from ISF with low protein concentration.
◆ The important Starling forces are the transendothelial pressure difference and the plasma–interstitial COP difference.
◆ Fluid is filtered from the arterial end of capillaries and absorbed from the venous end. Small proportion returns to the circulation as lymph.
◆ Raising plasma COP enhances absorption and shifts fluid from ISF to plasma.
◆ At supranormal capillary pressure, net filtration increases ISF volume
◆ At subnormal capillary pressure, net absorption increases plasma volume
◆ Infused colloid solution is distributed through the plasma volume, and infused ISS through the extracellular volume
This reassuringly simple paradigm is known to anybody who has studied medicine in the past century and is perpetuated in journals and textbooks to the present day.
Revised Starling equation and glycocalyx model requires us now to ditch the above concepts in their entirety. In their stead we should be teaching the following;
◆ Intravascular volume consists of a gel phase the glycocalyx volume, a sol phase the plasma volume, and red cell volume.
◆ Sinusoidal tissues (marrow, spleen, and liver) have discontinuous capillaries and their ISF is essentially part of the plasma volume.
◆ Open fenestrated capillaries produce the renal glomerular filtrate.
◆ Diaphragm fenestrated capillaries in specialized tissues can absorb exogenous fluid to plasma .
◆ Continuous capillaries exhibit ‘no absorption’.
◆ The EGL is semi-permeable to anionic proteins and their concentration in the intercellular clefts below the glycocalyx is very low.
◆ The important Starling forces are the transendothelial pressure difference and the plasma–subglycocalyx COP difference.
◆ ISF COP is not a direct determinant of Jv.
◆ Jv is much less than predicted by Starling’s principle, and the major route for return to the circulation is as lymph.
◆ Raising plasma COP reduces Jv but does not cause absorption.
◆ At subnormal capillary pressure, Jv approaches zero. Auto transfusion is acute, transient, and limited to about 500 ml.
◆ At supranormal capillary pressure, when the COP difference is maximal, Jv is proportional to transendothelial pressure difference.
◆ Infused colloid solution is initially distributed through the plasma volume, and infused ISS through the plasma volume plus glycocalyx volume.
◆ At supranormal capillary pressure, infusion of colloid solution preserves plasma COP, raises capillary pressure, and increases Jv.
◆ At supranormal capillary pressure, infusion of ISS also raises capillary pressure, but it lowers COP 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 ISS increases intravascular volume, but Jv remains close to zero in both cases.
Plasma volume, tissue oedema, and the steady-state Starling principle
Read about the steady state Starling principle applied to the control of plasma volume at the bedside.
Fluid Physiology: A Handbook for Anaesthesia and Critical Care Practice.
Woodcock T. Cambridge Scholars Publishing; 2019
Restricted or Liberal Fluid Therapy.
Understanding and extending the Starling Principle.
Michel CC, Woodcock TE, Curry FE. Understanding and extending the Starling Principle. Acta Anaesthesiol Scand. 2020;64:1032-1037.