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 (srvO2), and hemoglobin concentration (rvHb) during craniotomy.
Thirty-four patients were randomly assigned to a low propofol (4 mg/kg/h) versus a high propofol (6 mg/kg/h) group. A fiberoptic probe was applied on the cortex next to the surgical site. Measurements were performed during lower (35 mm Hg) and higher (45 mm Hg) levels of partial pressure of carbon dioxide (paCO2). Arterio-venous difference in oxygen concentration (avDO2) and approximated cerebral metabolic rate of oxygen (aCMRO2) were calculated for each paCO2 state. Linear models were fitted to test changes of end points in response to paCO2 and propofol concentration.
In comparison to the lower levels of paCO2, higher levels of paCO2 increased rvCBF (P<0.001), and srvO2 (P=0.002). RvHb remained unchanged during measurements (P=0.325). Calculated avDO2 decreased with increasing paCO2 (P<0.001), whereas aCMRO2 did not change during the study (P=0.999). Propofol concentration had no effect on measured or calculated end points.
Increase of rvCBF by paCO2 indicates a preserved CO2 reactivity independent of propofol anesthesia. The consecutive rise in srvO2 implies enhanced oxygen availability due to vasodilatation. Unchanged rvHb represents constant venous hemoglobin concentration. As expected, calculated avDO2 decreases with increased paCO2, whereas aCMRO2 remains unchanged. Despite the promising technical approach, the technology needs validation and further investigation for usage during neurosurgery.
Departments of *Anesthesiology
†Neurosurgery, University Hospital Medical Center, Johannes Gutenberg University, Mainz
‡Department of Chemistry and Biochemistry, Gene Center Munich, Ludwig Maximilians University, Munich, Germany
Financial Support: Supported by departmental funding.
There exists no financial relationship between the authors and the manufacturer of the O2C-device (LEA Medizintechnik GmbH, Giessen, Germany) or any other company or organization with potential or vested interest in the outcome of the study.
Reprints: Klaus Ulrich Klein, MD, Department of Anesthesiology, University Hospital Medical Center, Johannes Gutenberg University Langenbeckstrasse 1, 55131 Mainz, Germany (e-mail: firstname.lastname@example.org).
Received for publication April 29, 2009; accepted August 28, 2009
Remark: Parts of this work have been presented at the Annual Meeting of the American Society of Anesthesiologists, October 14 to 18, 2006, and the Society of Neurosurgical Anesthesia and Critical Care, October 13, 2006, Chicago, Illinois; and at the Annual Meeting of the American Society of Anesthesiologists, October 13 to 17, 2007, and the Society of Neurosurgical Anesthesia and Critical Care, October 12, 2007, San Francisco, California. Results of the present study were awarded with the clinical research prize 2008 (30.000 €) of the German Society of Anesthesiology and Intensive Care Medicine (Deutsche Gesellschaft für Anästhesiologie und Intensivmedizin, DGAI).
Implications Statement: Intraoperative routine monitoring of cerebral blood flow and oxygenation remains a technological challenge. In the present study, monitoring of brain tissue using a combination of photo-spectrometry and laser-Doppler flowmetry reproducibly assesses changes in cerebral microcirculation and oxygenation induced by CO2 changes.