Blood rheology compared in intravenous and halothane anaesthesia

Blood viscosity factors were compared in 28 adult ASA I and II surgical patients during intravenous (14 patients) and halothane (14 patients) anaesthesia lasting 45-60 minutes. Systolic and diastolic blood pressures, O 2 saturation and end-tidal CO 2 values were monitored continuously and checked by blood gas and pH analysis. Intravenous fluids (Ringer's lactate) were limited to 4 ml/kg/hour. While haematocrit was equally reduced (p < 0.005) in both groups, indicating comparable haemodilution, there were in the halothane group significantly greater reductions in (a) blood viscosity at all the five shear rates measured (230, 115, 46, 23 and 11.5 seconds 1), particularly at the lower two shear rates, (b) plasma viscosity and (c) fibrinogen and albumin concentrations in the plasma. These blood viscosity reductions point to a possible lessening of red blood cell aggregation with halothane anaesthesia, which then could have a rheological advantage over purely intravenous anaesthesia.