Fig. 1
In the normal brain, a progressive reduction of hemoglobin (Hb) is compensated for by vasodilation, which results in increased cerebral blood flow (CBF, black line) and a constant cerebral oxygen delivery (DO 2 , grey line). When Hb falls below 5–6 g/dl, DO2 is progressively reduced; no further vasodilation can occur and maximal CBF values (CBF max ) are obtained. The oxygen extraction rate (OER) then increases to meet metabolic tissue requirements