Intraoperative somatosensory evoked potentials (SSEP's) are being used with increasing frequency to monitor neurological function during spinal surgery. The authors report a case of postoperative paraplegia that occurred despite preserved intraoperative SSEP's in an achondroplastic dwarf who underwent correction of a congenital kyphoscoliosis. Surgeons and anesthesiologists involved with SSEP monitoring should be aware that false-negative results may occur with this technique.

Postoperative paraplegia with preserved intraoperative somatosensory evoked potentials. Case report.

https://www.annalsthoracicsurgery.org/article/S0003-4975(10)62499-X/pdf

Intraoperative detection of spinal cord ischemia using somatosensory cortical evoked potentials during thoracic aortic occlusion

Objective: To provide an educational service to the intraoperative neurophysiologist community by publishing a position statement by the American Society of Neurophysiological Monitoring on the recommended appropriate and correct use of somatosensory evoked potentials as an intraoperative neurophysiological monitoring tool to protect patient well-being during surgery. This position statement presents the somatosensory evoked potential utilization basis, relevant anatomy, patient preparation, important systemic factors, anesthesia considerations, safety and technical considerations, documentation requirements, neurophysiologist credentials and staffing practice patterns, and monitoring applications for protecting brain, spinal nerve root, peripheral nerve, plexus and spinal cord function. In conclusion, a summary of major recommendations regarding the use of somatosensory evoked potentials in intraoperative neurophysiological monitoring is presented.

Intraoperative monitoring using somatosensory evoked potentials. A position statement by the American Society of Neurophysiological Monitoring.

✓ The relationship of intraoperative monitoring of spinal cord somatosensory evoked potentials and postoperative deficit in 220 cases (121 with scoliosis, 41 with neoplasms, and 58 others) is reported. Bilateral posterior tibial nerve stimulation was used in 181 cases and unilateral median nerve stimulation in 39. Spinal cord (interspinous ligament needles), subcortical (neck surface), and cortical (scalp surface) SEP's were monitored. Seven patients had worsening of neurological function after surgery, three of whom demonstrated significant changes in SEP's monitored. In an additional four cases, there was more than a 50% decrease in amplitude of subcortical/cortical SEP's during monitoring, but no change in neurological status postoperatively. Combined monitoring of spinal cord, subcortical, and cortical SEP's enhanced the certainty of detecting spinal cord dysfunction even though there was a significant number of false-negative and false-positive results. A marked change in the SEP's indicated a high c...

Intraoperative spinal somatosensory evoked potential monitoring

In Reply: Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord.

As part of a study to determine if decompressive surgery benefits patients who have incomplete lesions of the spinal cord, the somatosensory evoked potential (SEP) has been employed as an intraoperative spinal cord monitor. This procedure was used to see if decompression results in any rapid changes in spinal cord conductivity and to correlate these findings with the patient's subsequent clinical course. In addition to trauma, however, other factors also affect the SEP, and these must be recognized if intraoperative monitoring is to be successful. Frequency of stimulation, wakefulness, and anesthetic agents alter the wave-form and amplitude of the SEP. Using nitrous oxide, oxygen, meperidine (or morphine), and a muscle relaxant for anesthesia, and stimulating at frequencies of 1 or 2 per second, 11 patients with cervical or upper thoracic lesions have been monitored. There was no loss or diminution of an SEP and no patient was neurologically poorer afterwards. In 4 patients, the SEP "improved" soon after decompression. Clinical outcome, however, was not related to whether the SEP changed or remained the same. In total, 8 patients subsequently improved functionally and 3 did not.

Ransohoff J

Papers

Somatosensory evoked potentials during decompression and stabilization of the spine. Methods and findings.