✔️Can be measured by Fick Principle
✔️This states that the uptake/ release of a substance e.g. O2 (Vo2) by an organ is the product of the blood flow (Q) through that organ and the arteriovenous difference in content (Cao2-Cvo2)
✔️This is applied using Kety-Schmidt technique where 10% Nitrous oxide is inhaled for 10-15 minutes, and the jugular venous concentration is measured and assumed to be the same as the brain concentration
✔️Once CBF is determined, additional values like CMRO2 and vascular resistance may be derived.
✔️N2O offers significant advantages over other agents used for the measurement of CBF in that it is safe, stable, cheap, readily available and has a partition coefficient unaffected by varying levels of lipid and water and hence is unlikely to change with age or cerebral oedema.
✔️CBF calculated by this technique represents the mean blood flow from the area of the brain draining into the particular jugular venous bulb being sampled: i.e. the ipsilateral cerebral hemisphere. Therefore, the Kety–Schmidt method of CBF measurement is unable to discriminate between grey and white matter and is insensitive to regional changes in flow.
Ref: Textbook of Neuroanaesthesia and Critical Care, Basil F Matta
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