IT IS GENERALLY conceded that the nitrous oxide technique developed by Kety and Schmidt1,2 is the most reliable method presently available for measurement of average cerebral blood flow (CBF) in man. Nevertheless, as may be expected, the method has some limitations. From a theoretical point of view, equilibrium of nitrous oxide gas between cerebral blood and brain tissue might not be complete within ten minutes, resulting in incomplete saturation of brain tissue which might produce some error. Furthermore, nitrous oxide is not an inert gas, although it is reasonable to assume that nitrous oxide is pharmacologically inert in the concentration of 15% used. A serious practical limitation is that samples of blood in excess of 50 ml must be drawn from the subject for each determination, resulting in considerable blood loss if repeated determinations are to be made. As originally described, indirect analysis of blood samples for nitrous oxide
GOTOH F, MEYER JS, TOMITA M. Hydrogen Method for Determining Cerebral Blood Flow in Man. Arch Neurol. 1966;15(5):549–559. doi:10.1001/archneur.1966.00470170103013
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