[Monitoring of short latent evoked potentials during brain stem surgery]

The studies were carried out in 33 patients with intrastem volumetric tumors. In 6 patients the monitoring was impossible because of technological problems. Somatosensory evoked potentials (SSEP) were recorded in 10 and acoustic stem evoked potentials (ASEP) in 18 out of 27 patients and the findings correlated to changes in the neurological status on day 1 postoperation. In 3 out of 9 patients operated on in a sitting posture SSEP monitoring during the main stage of the operation became impossible because the response disappeared due to an air layer above the parietal cortex. Transitory or constant changes in SSEP at the stage of tumor removal were detected in 5 patients. In 9 patients intraoperative changes in ASEP were recorded. False-positive results of ASEP monitoring were obtained in 4 cases. In 2 cases a discrepancy between intraoperative changes of SSEP and the postoperative neurologic deficit were detected. The authors discuss the technological and methodological problems of intraoperative monitoring of evoked potentials and approaches to solution of these problems.