Abstract
The predictability of pain makes surgery an ideal model for the study of pain and the development of strategies for analgesia and reduction of perioperative pain. As functional near-infrared spectroscopy reproduces the known functional magnetic resonance imaging activations in response to a painful stimulus, we evaluated the feasibility of functional near-infrared spectroscopy to measure cortical responses to noxious stimulation during general anesthesia. A multichannel continuous wave near-infrared imager was used to measure somatosensory and frontal cortical activation in patients undergoing catheter ablation of arrhythmias under general anesthesia. Anesthetic technique was standardized and intraoperative NIRS signals recorded continuously with markers placed in the data set for the timing and duration of each cardiac ablation event. Frontal cortical signals only were suitable for analysis in five of eight patients studied (mean age 14 ± 1 years, weight 66.7 ± 17.6 kg, 2 males). Thirty ablative lesions were recorded for the five patients. Radiofrequency or cryoablation was temporally associated with a hemodynamic response function in the frontal cortex characterized by a significant decrease in oxyhemoglobin concentration (paired t-test, p<0.05) with the nadir occurring in the period 4 to 6 seconds after application of the ablative lesion. Cortical signals produced by catheter ablation of arrhythmias in patients under general anesthesia mirrored those seen with noxious stimulation in awake, healthy volunteers, during sedation for colonoscopy, and functional Magnetic Resonance Imaging activations in response to pain. This study demonstrates the feasibility and potential utility of functional near-infrared spectroscopy as an objective measure of cortical activation under general anesthesia.
Highlights
Surgery results in nociceptor activation, inflammation at the surgical site, and nerve injury [1]
We demonstrate the feasibility of using Functional near-infrared spectroscopy (fNIRS) to measure cortical responses to noxious stimulation in patients under general anesthesia
The cortical signals produced by catheter ablation of arrhythmias mirror those seen with noxious stimulation in healthy volunteers and functional magnetic resonance imaging (fMRI) activations in response to pain
Summary
Surgery results in nociceptor activation, inflammation at the surgical site, and nerve injury [1]. By virtue of the abnormal perceptual response to normal sensory input, presents as hyperalgesia, allodynia, after sensations, and spread of pain to areas without discernible pathology. This topic has been reviewed elsewhere [1, 2, 3]. Consequences of central sensitization are plastic changes at a number of levels in the central nervous system, but especially the cortex, leading to altered and pathological behaviors referred to as maladaptive plasticity [4] Individuals vary in their perception of pain and response to tissue injury, and different pain patterns may be seen in the perioperative period. Objective and robust measures of nociceptive processing are a prerequisite to detect and prevent repeated nociceptive afferent discharges, central sensitization, and changes in brain systems [7]
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