Effect of haemodilution on experimental cerebral ischaemia.

The effect of normovolaemic haemodilution (HD) on cerebral ischaemia after middle cerebral artery occlusion (MCA) was studied. Thirteen adult cats (HD group, 5; control group, 8) were used. Systemic arterial pressure (SAP) was monitored continuously. MCA occlusion was produced by a transorbital approach. Regional cerebral blood flow (rCBF) in the ectosylvian region was measured by a hydrogen clearance method. The electroencephalogram (EEG) was monitored, and spectral power of the EEG was calculated. Pial artery pressure (PAP) in the ectosylvian region was continuously recorded non-occlusively by a micropressure recording device. In the HD group, low-molecular-weight dextran was given normovolaemically from 10 minutes after ischaemia to lower the haematocrit (Ht) to 24%. The rCBF values in the HD group were significantly higher than in the control group after 90 minutes. Upstream resistance [(SAP-PAP)/rCBF] was significantly lower in the HD group than in the control group. Furthermore, downstream resistance (PAP/rCBF) was significantly lower in the HD group than in the control group at the 180-minute point. There was no significant difference between the two groups in the spectral power of the EEG during ischaemia. The Ht was significantly correlated with rCBF in both groups. These results indicate that haemodilution can improve rCBF by lowering the Ht and improving the microcirculation of collateral vessels via pial anastomoses, although it might have insufficient effect on improvement of cerebral function.