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 (srvO2), and hemoglobin concentration (rvHb) during craniotomy.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Klein
Klaus Ulrich
KU
Department of Anesthesiology, University Hospital Medical Center, Johannes Gutenberg University, Mainz, Germany. kuklein@unimainz.de
Schramm
Patrick
P
Glaser
Martin
M
Reisch
Robert
R
Tresch
Achim
A
Werner
Christian
C
Engelhard
Kristin
K
D000328:Adult; D000368:Aged; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D001783:Blood Flow Velocity / Q000187:drug effects; D001921:Brain / Q000098:blood supply* / Q000187:drug effects / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D003399:Craniotomy / Q000379:methods; D004305:Dose-Response Relationship, Drug; D005240:Feasibility Studies; D005260:Female; D005336:Fiber Optic Technology; D005858:Germany; D006454:Hemoglobins / Q000187:drug effects; D006801:Humans; D017078:Laser-Doppler Flowmetry / Q000379:methods*; D008297:Male; D008833:Microcirculation / Q000187:drug effects*; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D010100:Oxygen / Q000378:metabolism*; D010783:Photometry / Q000379:methods; D015742:Propofol / Q000008:administration & dosage*; D013057:Spectrum Analysis / Q000379:methods
D018686:Anesthetics, Intravenous; D006454:Hemoglobins; D002245:Carbon Dioxide; D010100:Oxygen; D015742:Propofol