Monitoring of Brain Function by Means of Evoked Potentials in Cerebral Aneurysm Surgery
Deliberate arterial hypotension is currently used to operate upon cerebral aneurysms. However, it is not ascertained whether this practice is really safe for all patients, especially those presenting with preoperative vasospasm. 50 patients, requiring surgical treatment for cerebral aneurysm, have been submitted, during surgery, to the recording of Somatosensory Evoked Potentials (SEPs) on median nerve stimulation. This technique allows the functional evaluation of neural pathways mediating the somatosensory stimuli and of primary somatosensory cortex; it is known that a decrease of cerebral perfusion may affect the SEP waveforms in terms of reduced subcortical conduction velocity (i.e., increased central conduction time, CCT) and of reduced cortical response amplitude. These changes may be apparent before a permanent neurological damage is produced. Preoperative SEP recording demonstrated a prolonged CCT, possibly related to vasospasm, in 9 patients, a normal clinical evaluation notwithstanding (grade I and II).
During intraoperative deliberate hypotension, a SEP change has always been produced. No postoperative damage has been observed, however, as long as the CCT did not exceed 9 msec for 10 minutes (maximum normal CCT value is 6.7 msec) and as the cortical response had been visible throughout the whole surgical procedure. The critical value of CCT has been reached at a mean arterial pressure (MAP) lower than 60 Torr in patients with a normal preoperative SEP recording; at the opposite, in patients presenting with a prolonged preoperative CCT, the value of 9 msec was arrived at with a MAP value that is generally accepted as safe for all patients (75 Torr).
In conclusion, SEP monitoring has proved to be a useful technique to identify the minimum safe MAP value for the individual patient undergoing surgery for cerebral aneurysm.
KeywordsMean Arterial Pressure Cerebral Aneurysm Evoke Potential Somatosensory Evoke Potential Primary Somatosensory Cortex
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- 1.Ducati A, Pavani M, Cortellazzi P (1984) Somatosensory and acoustic-brainstem evoked responses in ischemic cerebrovascular diseases. Phronesis 4: 275–281.Google Scholar
- 2.Ducati A, Cenzato M, Landi A, Sironi VA, Massei R, Beretta L, Prati R, Bortolani E, Trazzi R (1987a) Intraoperative monitoring of Somatosensory Evoked Potentials and of Electroretinography during vascular surgery of supra-aortic trunks. Chirurgia Cardiovascolare III: 63–67.Google Scholar
- 3.Ducati A, Landi A, Cenzato M, Fava E, Ferrari de Passano C, Villani R (1987b) Monitoraggio intraoperatorio con potenziali evocati nella chirurgia degli aneurismi cerebrali. In: Paoletti P, Knerich R, Urcivoli R, Spairani C (eds) Attualita’ in Neurochirurgia. Monduzzi, pp 65-70.Google Scholar
- 4.Ducati A, Cenzato M, Landi A, Fava E, Signoroni G, Giovanelli M, Villani R (1988) BAEPs and SSEPs monitoring during posterior fossa surgery. In: Grundy BL, Villani R (eds) Evoked potentials: intraoperative and ICU monitoring. Springer, Wien New York, in press.Google Scholar
- 6.Grundy BL (1985) Intraoperative applications of evoked responses. In: Owen JH, Davis H (eds) Evoked potentials testing. Grune & Stratton, Inc, pp 159-212.Google Scholar
- 8.Jones SJ (1988) Normal and pathologic factor affecting sensory tracts potentials in the human spinal cord during surgery. In: Grundy BL, Villani R (eds) Evoked potentials: intraoperative and ICU monitoring. Springer, Wien New York, in press.Google Scholar
- 12.Koht A, Schramm J, Watanabe E, Schmidt G (1987) Somatosensory evoked potentials monitoring in cerebral aneurysms surgery. Clin Neurol Neurosurg 89-2/1:71.Google Scholar
- 13.Landi A, Ducati A, Cenzato M, Fava E, Arvanitakis D, Mulazzi D (1988) Somatosensory evoked potentials monitoring during cervical spine surgery. In: Grundy BL, Villani R (eds) Evoked potentials: intraoperative and ICU monitoring. Springer, Wien, in press.Google Scholar
- 18.Symon L, Wang ADJ (1986) Somatosensory evoked potentials: their clinical utility in patients with aneurysmal subarchnoid hemorrage. In: Cracco R, Bodis-Wollner I (eds) Evoked potentials. Alan R Liss, Inc, New York.Google Scholar