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Posterior tibial nerve and median nerve somatosensory evoked potential monitoring during carotid endarterectomy

[Le monitorage du potentiel évoqué somato-sensitif du nerf tibial postérieur et du nerf médian pendant l’endartériectomie de la carotide]

Pirjo Manninen, MD FRCPC^*, Roger Sarjeant, BS CNIM and Mital Joshi, BSCH MSc^*

^* From the Departments of Anesthesia and
Neurosciences, Toronto Western Hospital, University Health Network, University of Toronto, Toronto, Ontario, Canada.

Address correspondence to: Dr. Pirjo Manninen, Department of Anesthesia, Toronto Western Hospital, 399 Bathurst Street, Toronto, Ontario M5T 2S8, Canada. Phone: 416-603-5118; Fax: 416-603-6494; E mail: Pirjo.Manninen{at}uhn.on.ca

Purpose: Somatosensory evoked potential (SSEP) monitoring using the median nerve (MN) modality during carotid endarterectomy is well established. This study assessed the usefulness of monitoring the posterior tibial nerve (PTN) SSEP as an adjunct to MNSSEP for detection of cerebral ischemia and as an indicator for the insertion of a shunt in patients undergoing a carotid endarterectomy.

Methods: All patients undergoing carotid endarterectomy during three years who had routine bilateral MNSSEP were also monitored with bilateral PTNSSEP. Patients received a shunt if there was a significant change (> 50% decrease in amplitude of cortical peak (N20) in the MNSSEP after cross clamping. The incidence, timing, and duration of all PTNSSEP changes were compared to MNSSEP changes.

Results: One hundred fifty-three patients were studied. Significant changes in MNSSEP after cross clamp lead to insertion of a shunt in six patients. Changes in PTNSSEP occurred at almost the same time in three patients, four minutes before MNSSEP in one, three minutes later in one and no change in one patient. Good quality baseline tracings were obtained in 99% MNSSEP as compared to 88% PTNSSEP (P < 0.05). New postoperative neurological deficits occurred in four patients (2.6%), only one had significant evoked potential changes.

Conclusion: Monitoring of PTNSSEP is feasible and may be considered for an adjunct to MNSSEP or as an alternative modality if there are difficulties with MNSSEP. However, there may be a greater incidence of poor quality baseline tracings for PTNSSEP.