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Background and Methods: The infusion of dextran solutions is associated with haemodilution and, under some conditions, with a slight increase in plasma viscosity. To clarify the compound effects of simultaneous haemodilution and plasma viscosity increases on macro- and microhaemodynamics, we investigated the changes in arterial perfusion (radiolabelled microspheres, 15 microns ø) and oxygenation (tissue Po2) of vital organs using an animal model of plasma hyperviscosity. In nine splenectomized beagles plasma viscosity was increased step by step from 1.06 (baseline) to 2.14, and 2.99 mPa.s by infusion of small amounts (4% of total blood volume) of an ultra-high-molecular-weight dextran (50% w/v, mw: 500,000)., Results: Despite the significant increase in plasma viscosity, cardiac output as well as specific organ blood flows in heart, brain, liver, and muscle rose steadily with each step of viscosity, while the haematocrit declined from 0.31 to 0.24 and 0.20, respectively. Medians of tissue Po2 in liver peaked at a viscosity of 2 mPa.s and returned to baseline values at 3 mPa.s, whereas in non-working skeletal muscle Po2 values were maximal at 3 mPa.s., Conclusion: These results indicate that the impact of plasma viscosity on the rheological properties of whole blood is completely offset by the concomitant reduction of haematocrit. Thus, the comparatively minor changes in plasma viscosity observed after prolonged use of clinical dextrans and other colloids in no way compromise the perfusion and oxygenation of vital organs.

Background: The use of dextran solutions (DX) for hemodilution (HD) is considered being detrimental due to their effects on plasma viscosity., Methods: 14 splenectomized beagles (12.7 +/- 1.3 kg) were anesthetized and randomly assigned to HD to 20 vol% hematocrit (hct) with either 3 or 6% DX-60. The effects of HD upon nutritional organ blood flow (radioisotope-labelled microspheres, phi 15 microns), local tissue oxygenation (pO2 multiwire surface electrode), plasma and blood volume (131I-labelled dog albumin distribution), and macrohemodynamics were evaluated with regard to actual changes in hct and plasma viscosity, respectively., Results: Normovolemic HD with either solution resulted in equivalent changes in macrohemodynamics, and plasma and blood volume. Despite the increase in plasma viscosity associated with HD using 6% DX-60 (up to 1.45 +/- 0.10 mPa.s), blood flow rose in all organs studied (p < 0.05). After HD by means of 3% DX-60, plasma viscosity remained unchanged (1.09 +/- 0.04 mPa.s) but was not associated with higher organ blood flow as compared to 6% DX-60. In both groups, elevated pO2 values on the surface of liver and skeletal muscle (p < 0.01) as well as the shift in the pO2 histograms toward higher pO2 values indicated a more homogeneous tissue perfusion upon HD, independent of the diluent applied., Conclusion: In comparison to 6% DX-60, the solution of 3% DX-60 is of equivalent efficacy as volume substitute and in the induction of normovolemic HD. The main advantage of 3% DX-60 solution, however, is the fact that twice as much volume can be administered before the recommended maximal daily dose of 1.5 g/kg DX is reached. Of the rheological factors influencing oxygen delivery, hematocrit thus plays the predominant role, while plasma viscosity is of minor importance.

Oxygen delivery (systemic oxygen transport) is directly dependent upon cardiac output and oxygen content of the blood. The rheology of blood, however, represents a co-determinant of oxygen delivery. It has recently been argued that the increase in plasma viscosity occurring under hemodilution with dextran could be detrimental to blood flow and, hence, tissue oxygenation. METHODS. Twelve splenectomized beagles (12.5 +/- 1.7 kg) were anesthetized and randomly assigned to hemodilution to 20 vol% hematocrit (hct) with 6% hydroxyethyl starch (HES 200/0.62) or 6% dextran-70 (DX-70). The effects of hemodilution (HD) upon macrohemodynamics, plasma and blood volumes (131I dog albumin distribution), organ blood flow (radioactive-labelled microspheres, phi 15 microns), and local tissue oxygenation (pO2 multiwire surface electrode) were evaluated with special reference to any actual plasma viscosity. RESULTS. Moderate HD with either solution resulted in equivalent changes in macrohemodynamics and plasma and blood volumes. Tissue oxygen extraction increased (p less than 0.05) due to a small rise (maximally 28%) in cardiac output. HD with either solution resulted in an increase in plasma viscosity that was more pronounced in the DX-70 group (1.45 +/- 0.07 mPa.s) as compared to HES-diluted animals (1.16 +/- 0.04 mPa.s). Blood flow increased (p less than 0.01) in all organs after HD independently of the diluent. Both higher pO2 values on the surface of liver and skeletal muscle (p less than 0.01) as well as a shift of the pO2 histograms to the right indicated a more homogeneous tissue perfusion during HD. CONCLUSIONS. In normotensive animals without peripheral arterial occlusive disease undergoing moderate hemodilution, organ blood flow was independent of plasma viscosity. Systemic oxygen transport was not affected by plasma viscosity changes, but is primarily determined by systemic hct. Local surface tissue oxygenation on skeletal muscle and liver was not impaired, but rather improved during hemodilution despite raised plasma viscosity. Of the rheological factors influencing oxygen delivery, hct thus plays the predominant role while plasma viscosity is of minor importance.

The macro- and microcirculatory effect of small-volume resuscitation with hyperosmotic-hyperoncotic solutions was analyzed in 21 anesthetized beagles subjected to standardized traumatic-hemorrhagic hypotension (laparotomy and exteriorization of the intestine; MAP 40 mmHg for 75 min). Primary resuscitation consisted of bolus infusion of 10% of the blood loss (approx. 4 ml/kg) of either hyperosmotic (7.2%) saline -HSS-, hyperoncotic (10%) dextran 60 -HDS-, or hyperosomotic-hyperoncotic saline dextran (10% dextran 60 in 7.2% saline; HHS). Within 5 min CO was restored and systemic pressure significantly increased. In the HHS-group nutritional blood flow (RBF, measured by radiolabeled microspheres phi 15 microns) in kidneys, gastric mucosa, small intestine, colon, and pancreas was completely restored, while RBF to the myocardium, brain, and skeletal muscles exceeded baseline values. Despite the identical response in central hemodynamics, RBF to gastric mucosa, intestine, pancreas, and kidneys was significantly lower in HSS-animals (P less than 0.05 vs. HHS). In contrast, in the HDS-group CO, splanchnic, myocardial, and renal blood flow remained significantly reduced (P less than 0.05 vs. HHS). Despite the normalization of cardiac output by small volumes of hypertonic solutions, 7.2% saline alone failed to fully restore RBF after protracted traumatic hemorrhage. For the concept of small-volume resuscitation, the hyperosomotic-hyperoncotic solution of 10% dextran 60 in 7.2% saline appears to be most effective to improve organ perfusion during the prehospital period of trauma patients.