Quantifying the SSEP — the area under the curve

The use of neurophysiological evoked potentials for intraoperative monitoring of the spinal cord is rapidly increasing. There are a multitude of different techniques in use, each with claimed or proven advantages, and it is likely that a combination of complementary methods will eventually provide the most accurate and reliable surveillance of the cord at risk. A problem common to all techniques, whether sensory or motor, is the way in which the recorded response should be quantified. Response quantification is becoming increasingly important with the impending use of computerized or automated monitoring machines, a development which is being driven by the need to provide greater monitoring services as efficiently as possible. Computerized automation can certainly ease the burden on the technician or clinician of repetitive response acquisitions and probably improve the consistency of record keeping, but to provide any automation of the interpretation stage, including the plotting of trend lines, it is necessary to quantify the responses. The reliability and accuracy of this quantification is of medico-legal as well as clinical significance.