Internal jugular venous oxygen tension as an index of cerebral blood flow during carotid endarterectomy.

A QUANTITATIVE relationship between arterial carbon dioxide tension (Paco2) and cerebral blood flow (CBF) measured indirectly by the nitrous oxide or 85krypton techniques has been demonstrated by many investigators in normal manl4 and in anesthetized man.5-8 We have calculated this relationship to be CBF =1.31 Paco2+ 7.3 from the data of Kety and Schmidt' 2 who studied unanesthetized healthy subjects. In healthy subjects anesthetized with halothane, Alexander and associates8 found this relationship to be CBF= 1.37 PacO2 5.08 for PacO2 values between 19 and 56 mm Hg. In rhesus monkeys anesthetized with pentobarbital, Reivich9 who measured CBF with thermistor-flowmeter probes in both internal jugular veins, found an almost linear relationship between CBF and PacO2 values between 20 and 100 mm Hg. With Paco2 above 100 mm Hg, little or no further increase in CBF occurred. A similar linear relationship was found to exist between CBF and oxygen tension in the internal jugular vein (Pvo,) during halothane anesthesia in healthy subjects.7 Such a linear relationship can be expected under conditions of complete oxygenation of arterial blood, constant cerebral metabolic rate for oxygen (CMR02), and venous oxygen saturation between 20 and 65%, the linear portion of the venous blood oxygen dissociation curve. Woll-