Baseline Amplitude Ratios of Median Nerve Somatosensory Evoked Potentials: Clinical Implications During Carotid Endarterectomy.

Objectives: To (1) examine associations between the ipsi-to-contralateral median nerve somatosensory evoked potential (mSSEP) baseline amplitude ratio (=IAR) and clinical symptoms, cerebral infarction, or ischemic injury in the ipsilateral middle cerebral artery territory in patients undergoing carotid endarterectomy (CEA); and (2) evaluate the IAR as a predictor of clamp-induced ischemia.

Design: A retrospective cohort study.

Setting: Single-center study, Department of Anesthesiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

Participants: Patients after CEA with mSSEP monitoring between 2015 and 2019.

Intervention: A total of 221 patients were categorized into subgroups (S/I groups): asymptomatic or symptomatic patients without infarction and/or injury (-S/-I and +S/-I, respectively), symptomatic patients with old infarction (+S/+Io), and symptomatic patients with (sub-)acute infarction and/or injury (+S/+Ia). Predictors of clamp-induced ischemia were evaluated in 228 patients.

Measurements and main results: The effects of S/I groups, sex, age, and stenosis degrees on the IAR were tested in uni- and multivariable models. A statistically significant effect was found for "S/I groups." The mean IAR differed statistically significantly between the four subgroups (pF < 0.001); -S/-I, +S/-I, and +S/+Io had significantly higher mean IARs than the reference +S/+Ia. The association between predictor variables and a significant amplitude decline during carotid cross-clamping was examined using univariable and multivariable logistic regression models. A total of 16 of 228 patients (7%) experienced a significant amplitude decline. Solely contralateral carotid artery occlusion showed an indicated effect (odds ratio 4.21, 95% confidence interval 0.76-23.38, p = 0.1).

Conclusions: In CEA patients, a decreased IAR reflects the acuity of an infarction or injury but does not predict clamp-induced ischemia. Contralateral carotid artery occlusion showed a trend toward predicting clamp-induced ischemia.