Monitoring of cerebral oxygenation and local field potential with a variation of isoflurane concentration in a rat model

Abstract

Abstract:We aimed to investigate experimentally how anesthetic levels affect cerebral metabolism measured by near-infrared spectroscopy (NIRS) and to identify a robust marker among NIRS parameters to discriminate various stages of anesthetic depth in rats under isoflurane anesthesia. In order to record the hemodynamic changes and local field potential (LFP) in the brain, fiber-optic cannulae and custom-made microelectrodes were implanted in the frontal cortex of the skull. The NIRS and LFP signals were continuously monitored before, during and after isoflurane anesthesia. As isoflurane concentration is reduced, the level of oxyhemoglobin and total hemoglobin concentrations of the frontal cortex decreased gradually, while deoxyhemoglobin increased. The reflectance ratio between 730nm and 850nm and burst suppression ratio (BSR) correspond similarly with the change of oxyhemoglobin during the variation of isoflurane concentration. These results suggest that NIRS signals in addition to EEG may provide a possibility of developing a new anesthetic depth index. . 12(4), 1019-1029 (1996). 15. S. Ahn, T. Nguyen, H. Jang, J. G. Kim, and S. C. Jun, "Exploring neuro-physiological correlates of drivers' mental fatigue caused by sleep deprivation using simultaneous EEG, ECG, and fNIRS data," Front. Hum. Neurosci. 10, 219 (2016). 16. J. G. Kim, J. Lee, J. Roe, B. J. Tromberg, M. Brenner, and T. J. Walters, "Hemodynamic changes in rat leg muscles during tourniquet-induced ischemia-reperfusion injury observed by near-infrared spectroscopy,"

The changes of cerebral hemodynamics during ketamine induced anesthesia in a rat model

“…The selected LFP epochs during ketamine anesthesia were compared with LFP epochs during isoflurane anesthesia (Figure ). In our previous study, we calculated burst suppression ratio of the chosen LFP epochs to elaborate brain activity during isoflurane anesthesia . As shown in Figure A, isoflurane suppresses the LFP activity, and it can be quantified as the ratio of total time of suppression over epoch length.…”

“…Since our previous anesthetic agent, isoflurane, also increases CBF and CBV, we expected that a similar trend of hemoglobin concentration change would occur during ketamine anesthesia . Contrary to our expectations, the result shows an entirely different pattern of the hemoglobin concentration during ketamine anesthesia compared to isoflurane‐induced anesthesia.…”

“…Our NIRS system consists of a tungsten‐halogen light source (HL‐2000‐HP, Ocean Optics Inc., Largo, Florida) and a 16‐bit CCD spectrometer (USB4000, Ocean Optics Inc.) as a detector . Custom‐made optode with an optical fiber (0.39 NA, Ø400 μm Core, FT400EMT, Thorlabs) was used to illuminate the broadband light to the left frontal lobe.…”

“…If OHb and RHb are the major absorbers in the NIR range while scattering is constant, we can estimate the change of OHb and RHb with the following Eq. . where ∆ OD λ is the change of optical density at wavelength λ , whereas ε λ RHb and ε λ OHb are the extinction coefficients of OHb and RHb at wavelength λ , respectively. The light traveling path length in tissue is determined by d × DPF, where d is the source‐detector separation distance and DPF is the differential path length factor.…”

“…Since anesthesia induced respiratory change could induce significant CBV change, we calculated a ratio of reflectance intensity (RRI) between 730 and 850 nm wavelengths to deduct confounding effect . We normalized the reflectance of both 730 nm (R730) and 850 nm (R850) with 800 nm (R800) because at this wavelength OHb and RHb have identical extinction coefficient values (Eq.…”