We investigated the effects of reduced oxygen-carrying capacity on cardiac function during acute hemodilution, while the plasma viscosity was increased in anesthetized animals. Two levels of oxygen-carrying capacity were created by 1-step and 2-step hemodilution in male golden Syrian hamsters. In the 1-step hemodilution (1-HD), 40% of the animals' blood volume (BV) was exchanged with 6% dextran 70？kDa (Dx70) or dextran 2000？kDa (Dx2M). In the 2-step hemodilution (2-HD), 25% of the animals' BV was exchanged with Dx70 followed by 40% BV exchanged with Dx70 or Dx2M after 30 minutes of first hemodilution. Oxygen delivery in the 2-HD group consequently decreased by 17% and 38% compared to that in the 1-HD group hemodiluted with Dx70 and Dx2M, respectively. End-systolic pressure and maximum rate of pressure change in the 2-HD group significantly lowered compared with that in the 1-HD group for both Dx70 and Dx2M. Cardiac output in the 2-HD group hemodiluted with Dx2M was significantly higher compared with that hemodiluted with Dx70. In conclusion, increasing plasma viscosity associated with lowering oxygen-carrying capacity should be considerably balanced to maintain the cardiac performance, especially in the state of anesthesia. 1. Introduction Hemodilution reduces the circulating number of red blood cells (RBCs), decreases oxygen-carrying capacity, and lowers whole blood viscosity. To maintainf tissue oxygenation preventing multiorgan dysfunction, cardiac output (CO) increases to compensate for the reduction in oxygen-carrying capacity. The acute normovolemic hemodilution in anesthetized dogs revealed that myocardial blood flow significantly led an increased preservation of both myocardial oxygen-carrying capacity and consumption [1, 2]. Sufficient oxygen is normally offloaded from the hemoglobin in the RBCs unless the hematocrit (Hct) drops to very low values. There is a trigger point which is necessary to re-administer the RBCs into the circulation. The threshold for a blood transfusion is set at ~7？g of hemoglobin per 100？mL of blood. However, the findings by Tsai and Intaglietta [3] indicated that hemoglobin concentration can be lowered to 6？g/dL (18%？Hct) if the blood viscosity at a physiological level is maintained with a high viscosity plasma expander (HVPE). Other studies using an awake animal model as well as an anesthetized animal model have shown that microvascular function is impaired if the blood viscosity is severely decreased by hemodilution rather than an insufficient oxygen-carrying capacity [4–8]. A recent study by Chatpun and Cabrales [9]
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