Benefits and effectiveness of recording somatosensory evoked potentials in surgery on the carotid artery

Abstract

Operative treatment of high-grade carotid stenosis is an established procedure. The question whether a temporary - either selective or routine - shunt is needed, is a matter of controversy, and the decision is based on a number of available monitoring procedures. Within the framework of quality assurance based on the regular collection of our own patient data, carotid thromboendarterectomy (TEA) with recording of somatosensory evoked potentials (SEP) was analysed for its effectiveness. Two non-randomised groups of patients were analysed retrospectively: Group I: 99 carotid TEAs with no recording of SEP (1.1.99-31.12.99); Group II: 139 carotid TEAs with SEP recording (1.1.01-31.12.01). These two groups were unselected in terms of procedure, as also with regard to age, sex, stage or degree of carotid stenosis or surgeon, and were homogeneously distributed. A comparison was made of anaesthesia and operating times, shunt rate and the outcome of the two groups. Additionally, the two subgroups surgery with no shunt, and surgery with shunt, and the subgroups thromboendarterectomy with patchplasty (TEA) and eversion endarterectomy (EEA), were analysed. A temporary shunt was employed in 41 (41.4 %) of the patients in Group I (no SEP recording) and in 16 (11.5 %) of those in Group II (SEP recording). The average operating time in Group II was 11.4 min shorter (p < 0.001) than in Group I. The average carotid clamping time in Group II was significantly reduced (by 4.2 min; p < 0.001), while the duration of anaesthesia prior to skin incision was increased by an average of 18.3 min (p < 0.001), and the overall duration of anaesthesia by an average of 15.8 min (p < 0.001). A comparison of the subgroups surgery with no shunt and surgery with shunt revealed - both in Group I and Group II - a significant prolongation of the anaesthesia time and operating time (p < 0.001). In both Groups I and II, the subgroup TEA revealed a significant prolongation of both the anaesthesia and operating times vis-à-vis EEA. The major stroke rate was 2.0 % in Group I and 1.4 % in Group II, and the minor stroke rate 3.0 in Group I and 3.6 % in Group II; no deaths were observed. A reduction in the shunt rate to 11 % (by means of SEP) significantly decreased the average operating time (incision - suture) and the clamping time, with identical outcome in Groups I and II. Despite a reduction in the average incision-suture time in Group II (with SEP recording), the average overall operating time (anaesthesia time) was significantly increased due to the greater technical effort required. Carotid TEA with a selective shunt as determined by SEP is a high-cost procedure with no demonstrable benefit. At a stroke rate < 5 % and a need for stratification into several groups in accordance with the AHA classification, it is not possible to achieve adequate patient recruitment for a randomised analysis of outcome of the individual monitoring procedures. Alternative procedures are the routine use of a shunt and operation under regional anaesthesia.