Physiological alteration and anaesthetic drugs effects on intraoperative neurophysiological monitoring procedures

Intraoperative neurophysiological monitoring (IOM) and especially motor evoked potentials represents an important tool in the evaluation of the nervous system integrity and particularly of the motor tracts. A real and correct registration of the potentials with a proper interpretation of the modification is mandatory for an optimal outcome in eloquent areas, tumours, brainstem and medullary lesions. For all this to happen a suitable anaesthetic protocol must be used. Even though there is a large spectrum of anaesthetic agents at our disposal it is imperative to know their effect on the IOM signals recordings and the fact that some of them are dose-dependent. Drugs effects and physiological changes produced intraoperatively must be corrected before a shift in the direction of the surgical lesion resection it is taken. We present an overview of the action of the anaesthetic agents, most used protocols and the physiological alteration encountered in the operative theatre