Electrophysiologic measurements: Intraoperative evoked potential monitoring

Intraoperative electrophysiologic monitoring is important. Four conditions must exist for this technique to be of use: (1) the area of the central nervous system undergoing surgical intervention must be amenable to electrical monitoring; (2) sites must be available to both stimulate and then record the area of interest; (3) a neurophysiologist and the appropriate neurophysiologic monitoring equipment have to be available for monitoring; and (4) the surgeon and the anesthesiologist must both be prepared should any abnormalities arise to intervene and return any abnormal situations to a more physiologic state. The critical points include the avoidance of potent anesthetic agents during an important monitoring period. Should this not be possible, the neurophysiologist should be so informed. Blood levels of any of the anesthetic agents after induction should be kept at a constant level to reduce drug effect. Body temperature is a key factor in accurate monitoring. Stable and constant temperatures must be maintained throughout a case. Evoked potential monitoring is rapidly becoming a standard practice in neurosurgical operating rooms. An understanding of the principles and techniques involved and the measures an anesthesiologist can provide to prevent an impending neurologic deficit are the key elements to the successful outcome of many neurosurgical procedures.