Intraoperative Monitoring of Cerebral Microcirculation and Oxygenation-A Feasibility Study Using a Novel Photo-Spectrometric Laser-Doppler Flowmetry

Background: The present study assesses the utility of a novel invasive device (O2C-, oxygen-to-see-device) for intraoperative measurement of the cerebral microcirculation. CO2 vasoreactivity during 2 different propofol concentrations was used to investigate changes of capillary venous cerebral blood flow (rvCBF), oxygen saturation (srvO(2)), and hemoglobin concentration (rvHb) during craniotomy. Methods: Thirty-four patients were randomly assigned to a low propofol (4mg/kg/h) versus a high propofol (6mg/kg/h) group. A fiberoptic probe was applied on the cortex next to the surgical site. Measurements were performed during lower (35mm Hg) and higher (45mm Hg) levels of partial pressure of carbon dioxide (paCO(2)). Arterio-venous difference in oxygen concentration (avDO(2)) and approximated cerebral metabolic rate of oxygen (aCMRO(2)) were calculated for each paCO(2) state. Linear models were fitted to test changes of end points in response to paCO(2) and propofol concentration. Results: In comparison to the lower levels of paCO(2), higher levels of paCO(2) increased rvCBF (P<0.001), and srvO(2) (P = 0.002). RvHb remained unchanged during measurements (P = 0.325). Calculated avDO(2) decreased with increasing paCO(2) (P < 0.001), whereas aCMRO(2) did not change during the study (P = 0.999). Propofol concentration had no effect on measured or calculated end points. Conclusions: Increase of rvCBF by paCO(2) indicates a preserved CO2 reactivity independent of propofol anesthesia. The consecutive rise in srvO(2) implies enhanced oxygen availability due to vasodilatation. Unchanged rvHb represents constant venous hemoglobin concentration. As expected, calculated avDO(2) decreases with increased PaCO2, whereas aCMRO(2) remains unchanged. Despite the promising technical approach, the technology needs validation and further investigation for usage during neurosurgery.