Neurophysiological Monitoring during Surgery on the Central Nervous System: The Role of Evoked Responses

Neurosurgical, orthopedic and vascular interventions may be associated with an inherent risk of ischemia and structural damage to the central nervous system. Along with other modalities used to monitor the intraoperative nervous function, registration of evoked responses is intended to provide real-time feedback about the functional integrity of the central nervous system and help to prevent avoidable trauma during surgery. In this review, the principal indications and limitations of monitoring various evoked responses during surgery on the brain and spinal cord are discussed. Current approaches, recent advances and problems associated with intraoperative rhomboid fossa mapping, cranial nerve stimulation and electrooculographic monitoring are presented as well. The authors discuss the effects of general anesthesia on evoked responses and possible ways to avoid signal variability during registration. It is emphasized that only with close cooperation between neurosurgeons, anesthesiologists and neurophysiologists it will be possible to maximize the benefits of intraoperative monitoring of evoked responses and avoid misinterpretation of the results.