Monitoring of somatosensory evoked potentials during surgery for scoliosis in young adults: apropos of 33 cases

The risk of serious neurologic complications in spinal surgery for scoliosis is not insignificant. The recording of cortical somatosensory evoked potentials (CSEP) is an electrophysiological method of monitoring during surgery. Measurement of CSEPs was carried out before, during and after surgery in a preliminary series of 33 patients. These recordings were made: after induction of anesthesia and exposure of the spine; after instrumentation but without correction; after maximum traction; and at termination of surgery. The aim of this work was to establish alarm criteria. Statistical analysis showed a significant increase in latencies after instrumentation without correction, and after maximum traction. The alarm criteria were determined as an increase of more than 5 msec in the first positive deflection associated with an unusual drop in amplitude (over 75%). If these anomalies persist, the "wake-up test" must be used. In practice, this monitoring has often aided in reducing the period of surgery by using the "wake-up test" in a few selected cases.