[Is cerebral venous oxygen saturation an indicator of cerebral circulation?]

The arteriovenous oxygen content difference (avDO2) of the brain is dependent on O2 consumption (CM-RO2) and cerebral blood flow (CBF). With unchanging arterial O2 content, avDO2 is inversely related to cerebral venous O2 saturation (SO2). Measurement of SO2 in the jugular bulb not only provides information about the O2 balance of the brain, but may give an important estimation of CBF if a clinically useful correlation is proven. The aim of the present study was to verify this aspect. METHODS. Sixty-two male patients undergoing coronary revascularisation were investigated. The study was approved by the local Ethical Committee and each patient gave written informed consent on the preoperative day. At four points during the perioperative course arterial and cerebral venous SO2 and CBF were measured. Cerebral venous blood was sampled from a catheter in the superior bulb of the right internal jugular vein. CBF was measured using the argon wash-in technique. All sampled data were pooled and evaluated. RESULTS. As expected from theory, cerebral venous SO2 and avDO2 showed a close linear relationship (r = -0.892). However, only a weak hyperbolic relationship was found between cerebral venous SO2 and CBF. In addition, no direct correlation between CMRO2 and SO2 in the jugular bulb could be demonstrated. CONCLUSIONS. In this clinical study, a close relationship between cerebral venous SO2 and CBF was not found. This was primarily due to the high variability of cerebral O2 uptake. Changes in cerebral venous SO2 may therefore not be used as an estimate of perioperative changes in CBF.