Evoked potential monitoring and temporary clipping in cerebral aneurysm surgery

Temporary occlusion of the parent artery greatly facilitates the dissection of large cerebral aneurysms, while much reducing the risk of intraoperative rupture and avoiding the use of profound arterial hypotension. Intraoperative somatosensory evoked potential (SEP) monitoring was carried out in 25 aneurysm cases where temporary clipping was employed electively under moderate hypothermia. Occlusion times ranged from 6.3 to 52 minutes at 28.7 degrees C to 32.5 degrees C. Among 15 middle cerebral artery (MCA) occlusion cases the SEP was lost within 5 or 6 minutes in two cases undergoing early surgery and in one case with marked vasospasm and was lost within 9 minutes in one case with pre-existing infarction in the territory of the MCA. The SEP persisted throughout MCA occlusion periods of 6.3 to 52 minutes in 8 cases. Occlusion of parent arteries of unruptured aneurysms was well tolerated. At least 2 minutes of MCA occlusion after loss of the SEP were tolerated without neurological sequelae, while transient new deficits were seen when MCA occlusion was continued for 4 and for 4 + 11 minutes and an increased deficit was seen when occlusion was continued for 7 minutes after loss of the SEP. In each of the internal carotid artery (ICA) occlusion and bilateral anterior cerebral artery occlusion groups the SEP was lost in one case and was absent for about one minute before reperfusion was instituted. The ICA case had a transient deficit lasting about 4 hours; no other complications were seen in these two groups. Complications were not seen in any case where the SEP was not lost during the occlusion period. Factors affecting collateral perfusion and possible means of increasing tolerance to ischaemia in this situation are discussed.(ABSTRACT TRUNCATED AT 250 WORDS)