Rheological properties of commonly used plasma substitutes during preoperative normovolaemic acute haemodilution

Abstract

Preoperative normovolaemic acute haemodilution (PNAH) is used to reduce major blood loss during elective surgery. Considerable attention has been paid to colloid osmotic pressure, index of diffusibility and intravascular half-life of the currently available substitutes, but there is little information on their rheological properties from in vivo studies. Forty patients undergoing elective aortic reconstruction were given 4% human albumin (HA), 3.5% dextran 40 (Dxt 40), 6% dextran 60 (Dxt 60), 6% hydroxyethylstarch 200 (HES) or modified fluid gelatin (Gel) during PNAH to produce a packed cell volume (PCV) of approximately 30%. Mean volumes of more than 1000 ml were infused. Blood samples were obtained before infusion, immediately after, and 1.5 h after the end of haemodilution. The following variables were measured: PCV, plasma viscosity, whole blood viscosity at measured and corrected PCV (0.45), and erythrocyte aggregation. Haemodynamic and metabolic variables were determined at the same time. The five substitutes had very different effects on red blood cell aggregation and low shear rate viscosity at corrected PCV. Red blood cell aggregation was reduced in the presence of HA, Dxt 40, but was increased moderately to markedly in the presence of the other substitutes in the following order: HES < Dxt 60 < Gel. The influence of the rheological conditions on tissue oxygenation was assessed by measuring the concentration of lactic acid; this was unchanged after PNAH with HA or Dxt 40, but was increased in the presence of HES, Dxt 60 or Gel.

Assessment of hemodynamic and gastric mucosal acidosis with modified fluid gelatin versus 6% hydroxyethyl starch: a prospective, randomized study

“…Similar results have been reported by other authors with HES, MFG and albumin [14,15]. Both colloids decreased hemoglobin concentration by the same amount and increased cardiac index.…”

Randomized clinical trial comparing the effects on renal function of hydroxyethyl starch or gelatine during aortic aneurysm surgery

“…Explanations for these differences include improved haemorheology and reduced renal arteriolar vasoconstrictor release with HES solutions, or a reduction in renal capillary leak. HES 200/0·62 has been shown to reduce whole blood viscosity compared with gelatine during aortic surgery 15 . Since then, it has been shown that smaller molecules of starch reduce erythrocyte aggregation by preventing the bridges formed by macromolecules such as fibrinogen and large HES molecules 16 .…”

Effect of High- and Low-molecular-weight Low-substituted Hydroxyethyl Starch on Blood Coagulation during Acute Normovolemic Hemodilution in Pigs

“…However, no significant differences after hemodilution with HES 650/0.42 as compared with HES 130/0.42 have been observed by relating the decrease in hemoglobin concentration to the measured HES in vivo molecular weights ( fig. 6F) 26,27 The predominant rheologic effect of colloids consists in the reduction of whole blood viscosity proportional to the magnitude of their plasma volume expansion. 27 Plasma viscosity, however, is determined principally by the number and physical properties of dissolved macromolecules.…”