• Ke Peng, Deepti KarunakaranKeerthanaKFrom the Center for Pain and the Brain, Harvard Medical School, Boston, Massachusetts., Arielle Lee, Andrea Gomez-Morad, Robert Labadie, Arielle Mizrahi-Arnaud, Delany Berry, Barry Kussman, David Zurakowski, Lyle Micheli, Lino Becerra, and David Borsook.
• From the Center for Pain and the Brain, Harvard Medical School, Boston, Massachusetts; the Department of Neuroscience, Research Center of the University of Montreal Hospital Center, University of Montreal, Montreal, Quebec, Canada.
• Anesthesiology. 2021 Nov 1; 135 (5): 877-892.

BackgroundPatients undergoing surgical procedures are vulnerable to repetitive evoked or ongoing nociceptive barrage. Using functional near infrared spectroscopy, the authors aimed to evaluate the cortical hemodynamic signal power changes during ongoing nociception in healthy awake volunteers and in surgical patients under general anesthesia. The authors hypothesized that ongoing nociception to heat or surgical trauma would induce reductions in the power of cortical low-frequency hemodynamic oscillations in a similar manner as previously reported using functional magnetic resonance imaging for ongoing pain.MethodsCortical hemodynamic signals during noxious stimuli from the fontopolar cortex were evaluated in two groups: group 1, a healthy/conscious group (n = 15, all males) where ongoing noxious and innocuous heat stimulus was induced by a contact thermode to the dorsum of left hand; and group 2, a patient/unconscious group (n = 13, 3 males) receiving general anesthesia undergoing knee surgery. The fractional power of low-frequency hemodynamic signals was compared across stimulation conditions in the healthy awake group, and between patients who received standard anesthesia and those who received standard anesthesia with additional regional nerve block.ResultsA reduction of the total fractional power in both groups-specifically, a decrease in the slow-5 frequency band (0.01 to 0.027 Hz) of oxygenated hemoglobin concentration changes over the frontopolar cortex-was observed during ongoing noxious stimuli in the healthy awake group (paired t test, P = 0.017; effect size, 0.70), and during invasive procedures in the surgery group (paired t test, P = 0.003; effect size, 2.16). The reduction was partially reversed in patients who received a regional nerve block that likely diminished afferent nociceptive activity (two-sample t test, P = 0.002; effect size, 2.34).ConclusionsThese results suggest common power changes in slow-wave cortical hemodynamic oscillations during ongoing nociceptive processing in conscious and unconscious states. The observed signal may potentially promote future development of a surrogate signal to assess ongoing nociception under general anesthesia.Editor’s PerspectiveCopyright © 2021, the American Society of Anesthesiologists. All Rights Reserved.

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