Effects of temporary clips on somatosensory evoked potentials in aneurysm surgery

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.

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).

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.

There is no genuinely safe permissible occlusion time. Despite complete recovery of SEPs after a loss of potential, the patient may develop new deficits.