Effect of haemoglobin concentration on brain oxygenation in focal stroke: a mathematical modelling study.

Acute perioperative anaemia may affect neurological injury from permanent focal ischaemic insults. We modelled the opposing effects of haemodilution (increasing cerebral blood flow, decreasing arterial oxygen content) on oxygen availability and uptake in the ischaemic penumbra. First, we validated a mathematical model of regional cerebral oxygen uptake by using published arterial oxygen content and cerebral blood flow values from normal rabbits with progressive anaemia. Then we applied the model to the problem of interest (i.e. the ischaemic penumbra of a focal embolic stroke). We re-analysed published experimental data giving the cerebral blood flow response to anaemia in the ischaemic penumbra. Penumbral extraction reserves were nearly exhausted at a haemoglobin concentration of approximately 10g 100ml-1. Oxygen uptake in the ischaemic penumbra decreased progressively when haemoglobin concentrations decreased to less than 10g 100ml-1. We conclude that, given the available clinical and experimental literature, and until a suitable randomized clinical study has been performed, a haemoglobin concentration of 10 g 100 ml-1 is the rational transfusion "trigger" for the acutely anaemic stroke patient.