Comparison of cerebral metabolic rate of oxygen, blood flow, and bispectral index under general anesthesia

Abstract

Significance: The optical measurement of cerebral oxygen metabolism was evaluated.

Aim: Compare optically derived cerebral signals to the electroencephalographic bispectral index (BIS) sensors to monitor propofol-induced anesthesia during surgery.

Approach: Relative cerebral metabolic rate of oxygen ( ${\mathrm{rCMRO}}_2$ ) and blood flow (rCBF) were measured by time-resolved and diffuse correlation spectroscopies. Changes were tested against the relative BIS (rBIS) ones. The synchronism in the changes was also assessed by the R-Pearson correlation.

Results: In 23 measurements, optically derived signals showed significant changes in agreement with rBIS: during propofol induction, rBIS decreased by 67% [interquartile ranges (IQR) 62% to 71%], ${\mathrm{rCMRO}}_2$ by 33% (IQR 18% to 46%), and rCBF by 28% (IQR 10% to 37%). During recovery, a significant increase was observed for rBIS (48%, IQR 38% to 55%), ${\mathrm{rCMRO}}_2$ (29%, IQR 17% to 39%), and rCBF (30%, IQR 10% to 44%). The significance and direction of the changes subject-by-subject were tested: the coupling between the rBIS, ${\mathrm{rCMRO}}_2$ , and rCBF was witnessed in the majority of the cases (14/18 and 12/18 for rCBF and 19/21 and 13/18 for ${\mathrm{rCMRO}}_2$ in the initial and final part, respectively). These changes were also correlated in time ( $R>0.69$ to $R=1$ , $p\text{-}\text{values}<0.05$ ).

Conclusions: Optics can reliably monitor ${\mathrm{rCMRO}}_2$ in such conditions.

Keywords: bispectral index; cerebral blood flow; cerebral metabolic rate of oxygen; cerebral physiological changes; diffuse correlation spectroscopy; diffuse optics; near-infrared spectroscopy; propofol-induced anesthesia; time-resolved spectroscopy.

Fig. 1

(a) Bottom view of the 3D printed combined BIS-TRS/DCS probe. The first three electrodes of the BIS sensor are placed on the subject’s left forehead followed by the black fiber pad which fits around the BIS sensor. The fourth electrode is attached next to the patient’s left eye. Source (top) and detector (bottom) fiber tips are placed in between the first and second electrodes, surrounded by TangoBlack shore 27 material. (b) TRS and DCS acquired data in alternation. The intensity autocorrelation curves were calculated for 2.5 s, while the system switched through all three TRS lasers with an acquisition time of 800-ms per wavelength.

Fig. 2

Exemplification of the automatic segmentation by the Lavielle method. (a) The period of LOC for the variables of relevance (${\mathrm{rBIS}}_i$, ${\mathrm{OEF}}_i$, ${\mathrm{CBF}}_i$, and ${\mathrm{CMRO}}_{2i}$) in time is depicted. The period includes an initial baseline, a transition period and then another period that reaches a stable condition. The moments in the time axis where the segments split the time-traces are then collected. In the LOC, the anesthesia onset corresponds to the change point between the initial baseline and the beginning of the transition; while the time to reach stabilization coincides with the moment in which the transition ends and the new stability level is reached. (b) Similarly, on the right there is an example focused on the ROC. Here, the end of anesthesia onset and time to reach plateau are identified.

Fig. 3

Representative time evolution of the (a) BIS; (b) tissue oxygen saturation (${\mathrm{StO}}_2$); (c) rBIS. (d) The relative oxygen extraction fraction (rOEF); (e) the relative cerebral metabolic rate of oxygen extraction change (${\mathrm{rCMRO}}_2$); and (f) the relative CBF change (rCBF) during anesthesia induction ($t_0$ 3 minutes) by propofol (1%).

Fig. 4

Representative time evolution during ROC of the (a) BIS; (b) tissue oxygen saturation (${\mathrm{StO}}_2$); and (c) relative BIS (rBIS). The relative changes of (d) the oxygen extraction fraction (rOEF), e) the cerebral metabolic rate of oxygen extraction (${\mathrm{rCMRO}}_2$) and (f) the CBF (rCBF) are also shown at the end of the surgery performed under TIVA with propofol (1%) ($t_{\text{end}}$ 207 minutes).

Fig. 5

Data group visualization by boxplots for the periods of LOC and ROC. Both periods include the data distributions for the four variables (rBIS, rCBF, rOEF, and ${\mathrm{rCMRO}}_2$) around the group median and are all compared to their respective baseline period (either before anesthesia onset or recovery), which equals one and is represented by a dashed gray line. Percent changes of the medians are also reported close to arrows that show the direction (higher-up or lower-down) with respect to baseline. $P$-values for testing the difference of the group median with respect to baseline are reported. Asterisks indicate significant $p$-values. Subjects are color-coded in the same way for all variables.

Fig. 6

Linear regression plots for the four automatically retrieved time points identifying a change in the time-traces for all four variables of interest. BIS time is plotted versus CBF time, then versus OEF time and finally versus ${\mathrm{CMRO}}_2$ time. Pearson correlation coefficients $R$ and $p$-values are reported for each plot. Gray areas represent a 95% confidence interval built around the regression line.