Impact of Acute Normovolemic Hemodilution on Blood Viscosity

Acute normovolemic hemodilution (ANH) has long been employed for reducing allogenic blood transfusion for cardiac surgery, and hydroxyethyl starch has been used as an intravenous replacement fluid during ANH procedure. However, possible impact of ANH employing HES on blood viscosity and oxygen delivery have not been well investigated in patients undergoing off-pump coronary artery bypass (OPCAB) surgery . Anesthesia is induced and maintained by using propofol-remifentanil-rocuronium in OPCAB surgery (n=21). ANH is performed by using 5 ml/kg of blood salvage and administering 5 ml/kg of balanced HES 130/0.42 (Tetraspan™) for 15 min during vascular graft harvesting. For the present study, three arterial blood samples (3 ml each) are taken before (Sample 1) and after ANH (sample 2 and 3) and they are stored in 3 tubes. Sample 3 (in tube) undergoes further 30% in-vitro dilution by adding 1-1.5 ml HES. By using a scanning capillary tube viscometer (Hemovister™), Blood viscosity at low shear rate (5/sec) of the three samples are determined. By using a formula with blood viscosity and hematocrit, tissue O2 delivery index (TODI, = hematocrit/viscosity at 5/sec) is calculated.