[In vivo rheologic studies of plasma substitutes]

The aim of this study was to compare in 60 ASA1 patients, the rheological effects of a 500 ml plasma substitute infusion at induction of general anaesthesia. The 60 patients were allocated into 6 groups of 10. Each group received either albumin 4%, or dextran 40 3.5%, or dextran 60 6%, or hydroxyethylstarch (HES) 200 6%, or modified fluid gelatin or Ringer lactate. The infusion extended over 30 minutes. In blood samples obtained before infusion, immediately after the end, three and 24 hours after the end of infusion, osmotic pressure, oncotic pressure, proteins and fibrinogen concentration were measured. Following rheological parameters were also assessed: plasma viscosity, blood viscosity at two shear rates (0.5 and 128 s-1), erythrocyte aggregation by primary and final aggregation times as well as total and partial dissociation thresholds. The determinations were carried out at haematocrit corrected to 40%. At intergroup analysis of the different substitutes compared to albumin 4%, with the exception of Ringer lactate, there was no significant modification of osmotic and oncotic pressures or fibrinogen concentrations. Only gelatin and dextran 60 modified the rheological parameters. The intragroup comparison did not demonstrate significant variations of osmotic and oncotic pressures. Fibrinogen concentrations remained unchanged up to the 24th hours, where they increased as a reaction to surgery. Similar changes of rheological parameters occurred for Ringer lactate, albumin 4% and dextran 40: decrease of plasma viscosity (< 10%) and blood viscosity (< 20% at shear rate of 0.5 s-1), increase of primary aggregation time (30-50%) with decrease of total dissociation threshold (10-20%). These changes ended 24 hours after infusion. Dextran 60 and gelatin elicited a modification of blood rheology until the 24th hour after the end of infusion. Such modifications did not occur with HES. It is concluded that when a rheological effect is required albumin 4% or dextran 40 3.5% should be used.