Total intravenous anesthesia for intraoperative monitoring of the motor pathways: an integral view combining clinical and experimental data

Object. Monitoring of descending corticospinal pathways by using motor evoked potentials (MEPs) has proven to be useful in preventing permanent neurological deficits during cranial and spinal procedures. Difficulties in interpretation of intraoperative, changes in potentials may largely be attributed to the effects of anesthesia. Development of suitable intravenous anesthesia protocols specifically tailored for MEP monitoring, including plasma level target-controlled infusion (TCI), requires precise knowledge of the specific neurophysiological properties of the various agents. Methods. The effects of alfentanil, sufentanil, fentanyl, remifentanil, thiopental, midazolam, etomidate, ketamine, and propofol on neurogenic arid myogenic MEPs were evaluated in an integral study combining clinical data obtained in 40 patients and experimental investigations conducted in 140 animals. The dose-dependent modulation of MEPs after electrical and magnetoelectrical stimulation of the motor cortex was recorded from peripheral muscles and the spinal cord. The results were as follows opioids, propofol, and thiopental suppressed myogenic, but not neurogenic MEPs in a dose-dependent fashion; remifentanil. exerted the least suppressive effects. Etomidate and midazolam did not suppress myogenic MEP, even at plasma concentrations sufficient for anesthesia. Ketamine, induced moderate reduction of compound muscle action potential amplitudes only at high doses. Remifentanil and propofol administered via TCI systems allowed recording of myogenic potentials within a defined target plasma concentration range, Conclusions. Development of standardized total intravenous anesthesia/TCI protocols by using anesthetic agents such as propofol, remifentanil, ketamine, and midazolam, which have favorable pharmacokinetic and neurophysiological properties, will enhance the quality of intraoperative, MEPs and promote the use of MEP monitoring as a useful tool to reduce surgery-related morbidity.