In vitro colloid osmotic pressure of commonly used plasma expanders and substitutes: a study of the diffusibility of colloid molecules

Abstract

The rational choice of a plasma substitute for states of hypovolaemia depends partly on its colloid osmotic pressure (COP). We have measured the COP of 108 samples of plasma substitute across selectively permeable membranes which retain molecules greater than 10,000 dalton (COP10) and 50,000 dalton (COP50) the ratio COP50/COP10 providing a potential index of diffusibility of the smaller molecules across capillary membranes. 6% Hespan solution showed a particularly favourable COP50/COP10 ratio at 0.58 indicating a potential for good retention in the circulation whilst 3.5% Haemaccel showed a COP50/COP10 ratio of 0.18 indicating a potential for marked transcapillary diffusion, especially in states of capillary leak. In patients with normal capillary permeability both Gelofusine and Dextran 110 are likely to show adequate retention in the circulation with a COP50/COP10 ratio of 0.37 and 0.39 respectively. These are comparable to the retention of 4.5% human albumin (0.36) but all of the plasma substitutes tested, with the exception of Haemaccel, provided a higher COP across both membranes than 4.5% human albumin solution. An in vivo comparison of these plasma substitutes is required to confirm the advantages of macromolecular colloids in states of capillary leak.

Effects of extreme hemodilution with hemoglobin-based O2 carriers on microvascular pressure

“…Calibration of the osmometer was made with a 5% albumin solution using a 30-kDa cutoff membrane (Amicon; Danvers, MA) (30). The viscosity of plasma and whole blood was determined with a cone and plate viscometer at a shear rate of 160 s Ϫ1 at 37°C (Dv-IIϩ Viscometer, Brookfield Engineering Laboratories; Middleboro, MA).…”

Oxygen delivery and consumption in the microcirculation after extreme hemodilution with perfluorocarbons

“…Blood samples were centrifuged, and colloid osmotic pressure in plasma was measured (model 420, Colloid osmometer, Wescor; Logan, UT). Calibration of the osmometer was made with a 5% albumin solution using a 30-kDa cutoff membrane (Amicon; Danvers, MA) (33). The viscosity of plasma and whole blood was determined at a shear rate of 160 s Ϫ1 and 37°C in a Dv-IIϩ Viscometer (Brookfield Engineering Laboratories; Middleboro, MA).…”

Microvascular Po2during extreme hemodilution with hemoglobin site specifically PEGylated at Cys-93(β) in hamster window chamber

“…Viscosity was measured in a Brookfield DV-III cone/plate Rheometer with a CPE-40 cone spindle at a shear rate of 160 s Ϫ1 . COP was measured using a Wescor 4420 Colloid Osmometer (31). Oxygen equilibration curves were measured at 37°C using a Hem-O-Scan Aminco instrument (SLM Aminco Instruments; Urbana, IL).…”