Characterization of the functional near-infrared spectroscopy response to nociception in a pediatric population

Background: Near-infrared spectroscopy can interrogate functional optical signal changes in regional brain oxygenation and blood volume to nociception analogous to functional magnetic resonance imaging. Aims: This exploratory study aimed to characterize the near-infrared spectroscopy signals for oxy-, deoxy-, and total hemoglobin from the brain in response to nociceptive stimulation of varying intensity and duration, and after analgesic and neuromuscular paralytic in a pediatric population. Methods: We enrolled children 6 months-21 years during propofol sedation before surgery. The near-infrared spectroscopy sensor was placed on the forehead and nociception was produced from an electrical current applied to the wrist. We determined the near-infrared spectroscopy signal response to increasing current intensity and duration, and after fentanyl, sevoflurane, and neuromuscular paralytic. Heart rate and arm movement during electrical stimulation was also recorded. The near-infrared spectroscopy signals for oxy-, deoxy-, and total hemoglobin were calculated as optical density*time (area under curve). Results: During electrical stimulation, nociception was evident: tachycardia and arm withdrawal was observed that disappeared after fentanyl and sevoflurane, whereas after paralytic, tachycardia persisted while arm withdrawal disappeared. The near-infrared spectroscopy signals for oxy-, deoxy-, and total hemoglobin increased during stimulation and decreased after stimulation; the areas under the curves were greater for stimulations 30 mA vs 15 mA (13.9 [5.6-22.2], P =.0021; 5.6 [0.8-10.5], P =.0254, and 19.8 [10.5-29.1], P =.0002 for HbO₂, Hb, and Hb_T, respectively), 50 Hz vs 1 Hz (17.2 [5.8-28.6], P =.0046; 7.5 [0.7-14.3], P =.0314, and 21.9 [4.2-39.6], P =.0177 for HbO₂, Hb, and Hb_T, respectively) and 45 seconds vs 15 seconds (16.3 [3.4-29.2], P =.0188 and 22.0 [7.5-36.5], P =.0075 for HbO₂ and Hb_T, respectively); the areas under the curves were attenuated by analgesics but not by paralytic. Conclusion: Near-infrared spectroscopy detected functional activation to nociception in a broad pediatric population. The near-infrared spectroscopy response appears to represent nociceptive processing because the signals increased with noxious stimulus intensity and duration, and were blocked by analgesics but not paralytics.