Raising plasma COP reduces J v but does not cause absorptionĪt subnormal capillary pressure, net absorption increases plasma volumeĪt subnormal capillary pressure, J v approaches zero. Raising plasma COP enhances absorption and shifts fluid from ISF to plasma J v is much less than predicted by Starling's principle, and the major route for return to the circulation is as lymph Small proportion returns to the circulation as lymph ISF COP is not a direct determinant of J vįluid is filtered from the arterial end of capillaries and absorbed from the venous end. The important Starling forces are the transendothelial pressure difference and the plasma–subglycocalyx COP difference. The important Starling forces are the transendothelial pressure difference and the plasma–interstitial COP difference The EGL is semi-permeable to anionic proteins and their concentration in the intercellular clefts below the glycocalyx is very low Open fenestrated capillaries produce the renal glomerular filtrateĭiaphragm fenestrated capillaries in specialized tissues can absorb ISF to plasmaĬontinuous capillaries exhibit ‘no absorption' Sinusoidal tissues (marrow, spleen, and liver) have discontinuous capillaries and their ISF is essentially part of the plasma volume Intravascular volume consists of glycocalyx volume, plasma volume, and red cell distribution volumeĬapillaries separate plasma with high protein concentration from ISF with low protein concentration Intravascular volume consists of plasma and cellular elements Revised Starling equation and glycocalyx model Table 1 Comparison of the original and revised paradigms for prescribing fluid therapy Original Starling principle Any potential advantage of plasma or plasma substitutes over crystalloids for volume expansion only manifests itself at higher capillary pressures. An explanation for the phenomenon of context sensitivity of fluid volume kinetics is offered, and the proposal that crystalloid resuscitation from low capillary pressures is rational. The EGL excludes larger molecules and occupies a substantial volume of the intravascular space and therefore requires a new interpretation of dilution studies of blood volume and the speculation that protection or restoration of the EGL might be an important therapeutic goal. Filtered fluid returns to the circulation as lymph. The oncotic pressure difference across the EGL opposes, but does not reverse, the filtration rate (the ‘no absorption' rule) and is an important feature of the revised paradigm and highlights the limitations of attempting to prevent or treat oedema by transfusing colloids. The characteristics of capillaries in various tissues are reviewed and some clinical corollaries considered. The revised Starling equation based on recent research considers the contributions of the endothelial glycocalyx layer (EGL), the endothelial basement membrane, and the extracellular matrix. Fluid therapy to support the circulation relies on applying a physiological paradigm that better explains clinical and research observations. fluid therapy does not result in the extracellular volume distribution expected from Starling's original model of semi-permeable capillaries subject to hydrostatic and oncotic pressure gradients within the extracellular fluid. Special Issue on Memory and Awareness in Anesthesia (PDF).Special Issue on Mass Casualty Medicine and Anaesthesia: Science and Clinical Practice (JPG).Special Issue on Thoracic Anaesthesia and Respiratory Physiology (PDF).Hong Kong College of Anaesthesiologists.College of Anaesthesiologists of Ireland.Memory, Awareness and Anaesthesia 2022 Special Collection.COVID-19 and the Anaesthetist: A Special Series.
0 Comments
Leave a Reply. |