Sensory evoked potentials: a system for clinical testing and patient monitoring

There is increasing interest in the use of averaged sensory evoked potentials for diagnostic testing and patient monitoring. This testing technique offers an opportunity to obtain information on function in the central nervous system and can be used in uncooperative and comatose patients. However, in the clinical situation background noise is often high, due for example to posturing by the patient, and even with extensive signal averaging it can be difficult to determine whether a response is present. This paper describes a data acquisition technique we have implemented for patient testing in the intensive care unit and the operating room to facilitate analysis of the responses. The averaging system delivers the stimulus in the middle of the data window, providing a pre-stimulus control interval from which to estimate residual background noise in the average. In addition, two averages are formed simultaneously to determine reproducibility of the response. This technique has been modified to provide a method of continuous monitoring that allows rapid detection of large changes in the response plus automatic tracking of selected response peak parameters.