[Evaluation of the capacities of neurophysiological intraoperative monitoring in reconstructive surgery on the vertebral column].

Aim: To evaluate the capacities of neurosurgical intraoperative monitoring of somatosensory evoked potentials (SSEP) in reconstructive operations on the vertebral column.

Materials And Methods: The Center of Spinal Surgery examined 30 patients treated in February to July 2001. According to the diagnosis, the distribution was as follows: degenerative diseases of the vertebral column (80%), its tumors (10%), injury (7%), and inflammatory diseases (3%). Of them, 13 (43.3%) patients underwent anterolateral decompression of the dural sac of roots, 17 (56.7%) had traditional decompression of the dural sac and roots from the posterior access. The study was carried out on an 8-channel electrophysiological Viking-IV system (Nicolet, USA). Intraoperative SSEP monitoring was made by the routine procedure. The amplitude and latent time of subcortical peaks (P31) were determined at surgery. Intraoperative SSEPs were classified as defined with the American Electroencephalographic Society. The changes in the basic parameters of SSEP were also divided into transient (under 30 minutes) and permanent (above 30 minutes).

Results: True positive responses (significant changes in intraoperative SSEPs and the presence of postoperative neurological disorders) were 3.3% (1 patient); false positive ones (significant changes in intraoperative SSEPs without postoperative neurological disorders) were 23.3% (7 patients). False negative responses (normal intraoperative SSEPs and the presence of postoperative neurological disorders) were absent. The findings indicate that new postoperative neurological disorders should not be expected in patients with the clinical picture of mild neurological disorders if they have transient changes in the basic parameters of SSEPs that last at least 30 minutes. At the same time a risk group includes patients with severe neurological disorders since in these patients, compensatory capacities are primarily decreased and intraoperative exposures may result in early spinal circulatory decompensation. More frequent (every 10 minutes) recording of intraoperative SSEPs is also recommended for this group of patients is complicated surgical manipulations.

Conclusions: 1. Neurophysiological intraoperative monitoring yields additional information for surgeons during an operation. 2. During intraoperative monitoring of SSEPs, it is necessary to assess any changes in the latter as true and to immediately find possible causes of these changes. 3. In patients with revealed spondylogenic spinal circulatory disorders and severe neurological disorders, even short-term changes in SSEPs should be assessed with particular carefulness before surgery.