The Effect of Xenon-Based Anesthesia on Somatosensory-Evoked Potentials in Patients Undergoing Carotid Endarterectomy.

OBJECTIVES: The aim of this study was to investigate the influence of xenon-based anesthesia on somatosensory-evoked potentials. DESIGN: Observational cohort study. SETTING: University hospital. PARTICIPANTS: Twenty subsequent adult patients undergoing elective carotid endarterectomy. INTERVENTIONS: Xenon-based anesthesia. MEASUREMENTS AND MAIN RESULTS: Cortical-evoked responses to median nerve stimulation were quantified by measurement of the amplitude and latency of the N20 wave, which are typically assessed during carotid surgery to detect intraoperative cerebral hypoperfusion and ischemia. Primary (N20 amplitude and latency) and secondary (mean arterial pressure, norepinephrine requirements and depth of anesthesia) were assessed during (1) propofol/remifentanil and (2) subsequent xenon/remifentanil anesthesia. Xenon at an inspiratory fraction of 62.5 ± 7% decreased norepinephrine requirement (0.067 ± 0.04 v 0.028 ± 0.02 µg/kg/min, p < 0.001), and mean arterial pressure was unchanged (90.6 ± 15.0 v 93.1 ± 9.6 mmHg, p = 0.40). Somatosensory-evoked potentials were available in all patients during xenon/remifentanil. Despite similar depth of anesthesia (Narcotrend index 38.4 ± 6.2 v 38.5 ± 5.8) during propofol and xenon, N20 amplitude was reduced after xenon wash-in from 3.7 ± 1.7 to 1.4 ± 2.8 µV, p < 0.001 on the surgical and 3.6 ± 1.6 to 1.4 ± 0.6 µV, p < 0.001 on the contralateral side. N20 latency remained unchanged during xenon (22.9 ± 2.1 v 22.5 ± 2.8 ms, p = 0.34 and 22.9 ± 2.0 v 22.9 ± 3.0, p = 0.97). CONCLUSIONS: Xenon influences somatosensory-evoked potentials measurement by reducing N20 wave amplitude but not latency. When xenon is considered as an anesthetic for carotid endarterectomy, wash-in needs to be completed before carotid surgery is commenced to provide stable baseline somatosensory-evoked potential measurement.