[Somatosensory evoked potentials (SEP) by isoflurane and enflurane in cardiosurgical interventions]

In the order to gain further insight into the sensory nervous pathways during enflurane- and isoflurane anaesthesia, two different concentrations (1 and 2 vol.%) of the anaesthetics were given to patients during extracorporeal circulation in normothermia and normocarbia, while somatosensory-evoked potentials (SEP) were recorded. As SEP-changes either reflect a change in functional integrity of the sensory nervous pathways (amplitude suppression) and a change in the speed of conduction (latency changes), the central effects of the volatile anaesthetics could be more fully evaluated. Isoflurane as well as enflurane induced a concentration-related change in latency especially of the late N100-component. However, in contrast to isoflurane administration the isomer enflurane in the high concentration range (2 vol.%) induced an increase of amplitudes of the early N20 and late N100-peak. Such an increase in amplitudes is interpreted as a disinhibition of medullary inhibitory centres, a possible premonitory sign of epileptogenic cortical activity, which already had been observed by various investigators.