TOTAL INTRAVENOUS ANESTHESIA FOR IMPROVEMENT OF INTRAOPERATIVE MONITORING OF SOMATOSENSORY EVOKED-POTENTIALS DURING ANEURYSM SURGERY

TWO ANESTHETIC REGIMENS for monitoring somatosensory evoked potentials (SEPs) during intracranial aneurysm surgery were compared. Eighty-four sequential cases of intracranial aneurysms were operated on employing SEP monitoring. The first group of 22 cases was anesthetized with "balanced anesthesia" and the second group of 62 cases received total intravenous anesthesia (TIVA) consisting of propofol and alfentanil. In the TIVA group, the amplitude of early cortical SEP responses (N20-P25, or P40-N50) was significantly higher than that of responses in the balanced anesthesia group. In median nerve SEPs, the averaged amplitude of N20-P25 was 3.22 muV with TIVA and 1.69 muV with balanced anesthesia (P = 0.006). Similarly, posterior tibial nerve SEPs showed a P40-N50 response of 1.8.5 muV and 1.00 muV, respectively (P = 0.01 7). The superior signal-to-noise ratio obtained with TIVA allowed more frequent and reliable intraoperative SEP recordings than was possible with balanced anesthesia, resulting in rapid and reliable feedback for the surgeon. In 19% of median nerve SEPs recorded with TIVA, the cortical responses were over 5 muV in amplitude, so that reproducible N20-P25 responses were obtainable by averaging only 10 to 50 serial responses, that is, two to three recordings per minute. The higher amplitude of posterior tibial nerve SEPs recorded with TIVA made monitoring during surgery for anterior communicating artery aneurysms possible in all cases. This was not always the case with balanced anesthesia. The late deflection of median nerve SEPs (N30) was more frequently observed with TIVA. It is a more sensitive indicator of cortical hypoperfusion than the N20-P25 complex, which adds additional information. This new anesthetic protocol consisting of propofol and alfentanil was useful for intraoperative SEP monitoring and was safe to use during aneurysm surgery.