• Jesus Pujol, Gerard Martínez-Vilavella, Lluís Gallart, Laura Blanco-Hinojo, Susana Pacreu, Vincent Bonhomme, Joan Deus, Víctor Pérez-Sola, Pedro L Gambús, and Juan Fernández-Candil.
• MRI Research Unit, Department of Radiology, Hospital Del Mar, Barcelona, Spain; Centro Investigación Biomédica en Red de Salud Mental, CIBERSAM G21, Barcelona, Spain. Electronic address: 21404jpn@comb.cat.
• Br J Anaesth. 2023 Feb 1; 130 (2): e330e338e330-e338.

BackgroundThe safety of anaesthesia has improved as a result of better control of anaesthetic depth. However, conventional monitoring does not inform on the nature of nociceptive processes during unconsciousness. A means of inferring the quality of potentially painful experiences could derive from analysis of brain activity using neuroimaging. We have evaluated the dose effects of remifentanil on brain response to noxious stimuli during deep sedation and spontaneous breathing.MethodsOptimal data were obtained in 26 healthy subjects. Pressure stimulation that proved to be moderately painful before the experiment was applied to the thumbnail. Functional MRI was acquired in 4-min periods at low (0.5 ng ml-1), medium (1 ng ml-1), and high (1.5 ng ml-1) target plasma concentrations of remifentanil at a stable background infusion of propofol adjusted to induce a state of light unconsciousness.ResultsAt low remifentanil doses, we observed partial activation in brain areas processing sensory-discriminative and emotional-affective aspects of pain. At medium doses, relevant changes were identified in structures highly sensitive to general brain arousal, including the brainstem, cerebellum, thalamus, auditory and visual cortices, and the frontal lobe. At high doses, no significant activation was observed.ConclusionsThe response to moderately intense focal pressure in pain-related brain networks is effectively eliminated with safe remifentanil doses. However, the safety margin in deep sedation-analgesia would be narrowed in minimising not only nociceptive responses, but also arousal-related biological stress.Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.

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