ISOFLURANE ANESTHESIA BLUNTS CEREBRAL RESPONSES TO NOXIOUS AND INNOCUOUS STIMULI - A FMRI STUDY

We used functional magnetic resonance imaging to determine how isoflur ane affected cerebral neuronal activation resulting from noxious and i nnocuous stimuli. Five male volunteers were subjected to mild electric al shock and tactile stimuli applied to the hand. During low (0.7%) an d moderate (1.3%) isoflurane anesthesia the stimuli were repeated and a supramaximal electrical shock was also applied. Tactile stimulation activated bilateral SI and SII, but resulted in no significant activat ion at low or moderate anesthesia. Electrical shock activated contrala teral SI and bilateral SII; low anesthesia completely abolished this r esponse. The supramaximal stimulus activated the caudate nucleus and b ilateral thalamus at low anesthesia; these responses were diminished a t moderate anesthesia. Isoflurane anesthesia blunts cerebral responses to somatosensory stimuli, and the absence of cortical activation duri ng supramaximal stimulation suggests that noxious-induced movement is generated in lower CNS structures. (C) 1997 Elsevier Science Inc.