Blood viscosity, hemodynamics and vascular hindrance in a rat model of acute controlled bleeding and volume restitution with blood or Haemaccel

Background: Hemorrhage and volume restitution with commercially available s olutions is followed by reduced blood viscosity. Consequent hemodynamic cha nges may arise not only from the reduced viscosity itself but also from cha nges in vascular geometry induced by autoregulation processes. Vascular hin drance reflects the contribution of vascular geometry to flow Our aim was t o explore the possible effects of blood volume restitution with Haemaccel o r blood, on regional blood flow and vascular geometry. Methods: Under ketamine anesthesia, blood was withdrawn at a rate of 0.3 ml /min for 15 min followed by 15 min of stabilization. The shed blood or Haem accel was infused at the same rate and volume as used for withdrawal. Hemod ynamic measurements were performed using radioactive microspheres. Blood vi scosity was measured with an Ostwald viscometer. Vascular hindrance was cal culated as the resistance/viscosity ratio. Results: Volume replacement with Haemaccel (n=10), compared to blood (n=10) , was followed by increased cardiac output and portal venous inflow (37.1+/ -9.0 and 3.1+/-0.5 vs 25.9+/-6.8 and 2.2+/-0.9 ml.min(-1) 100 g bw(-1), res pectively; P<0.05), de-creased viscosity (2.8+/-1.3 vs 3.7+/-1.3, respectiv ely; P<0.01) and decreased peripheral and splanchnic arteriolar resistance (3.8+/-1.1 and 40.9+/-7.6 vs 5.2+/-1.7 and 61.1+/-29.5 mmHg . ml(-1) . min 100 g bw, respectively; P<0.05). No significant differences between the gro ups were observed in vascular hindrance and cardiac output distribution. Conclusion: Volume replacement with Haemaccel, compared to blood, induced i ncrease in systemic and splanchnic blood flows, reflecting mainly changes i n viscosity and not in blood vessel geometry. These results suggest no sign ificant difference in overall activation of autoregulation process between volume restitution with blood or Haemaccel.