Effects of temporary clips on somatosensory evoked potentials in aneurysm surgery.

INTRODUCTION: Changes in somatosensory evoked potentials (SEPs) were used to identify cerebral ischemia and to predict neurological outcome during the application of temporary clips in aneurysm surgery.
METHODS: SEPs were recorded intra-operatively in 76 patients with 79 aneurysms (8 in the posterior fossa). Twenty aneurysms ruptured during surgery, and 37 temporary clips were applied over an average of 8.1 minutes (range: 2-25 minutes).
RESULTS: Of 17 cases with complete loss of potential, 14 were associated with temporary clips. Two losses were persistent with postoperative neurological deficit after 10 minutes of clipping. Six showed incomplete recovery after a mean loss of 19.2 minutes following clipping of 9.3 minutes, resulting in a new deficit in four patients. Despite complete recovery of potential in six patients after a 1 loss over 18.8 minutes following clipping of 10.7 minutes, four patients developed neurological deficits. The sensitivity of SEPs in determining permanent neurological deficits was 57%, and the was specificity 88%. The duration of temporary clipping was significantly shorter in patients without resulting new neurological deficit (Mann-Whitney Test; p < 0.01). The risk of a new deficit was 30.7% in cases where less than 8 minutes of clipping was performed, and the risk was 80.9% when clipping exceeded 8 minutes. The extent of recovery of potentials and the duration of SEP changes was strongly associated with the postoperative deficits (Kolmogorov-Smirnov Test, p = 0.009; p = 0.001, Mann-Whitney Test). Pathological p(ti)O2 measurements were obtained in 6 of 12 patients. In four patients, temporary occlusion was followed by a parallel alteration of SEPs and p(ti)O2 below 10 mmHg.
CONCLUSION: There is no genuinely safe permissible occlusion time. Despite complete recovery of SEPs after a loss of potential, the patient may develop new deficits.