0018-9294 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TBME.2017.2703951, IEEE Transactions on Biomedical Engineering TBME-01614-2016.R1 Copyright (c) 2016 IEEE. Personal use of this material is permitted. However, permission to use this material for any other purposes must be obtained from the IEEE by sending an email to pubs-permissions@ieee.org. 1 Abstract— Introduction: Neurophysiologic monitoring can improve autonomic nerve sparing during critical phases of rectal cancer surgery. Objectives: To develop a system for extracorporeal stimulation of sacral nerve roots. Methods: Dedicated software controlled a ten-electrode stimulation array by switching between different electrode configurations and current levels. A built-in impedance and current level measurement assessed the effectiveness of current injection. Intra-anal surface electromyography (sEMG) informed on targeting the sacral nerve roots. All tests were performed on five pig specimens. Results: During switching between electrode configurations, the system delivered 100% of the set current (25 mA, 30 Hz, 200 μs cathodic pulses) in 93% of 250 stimulation trains across all specimens. The impedance measured between single stimulation array contacts and corresponding anodes across all electrode configurations and specimens equaled 3.7 ± 2.5 kΩ. The intra-anal sEMG recorded a signal amplitude increase as previously observed in the literature. When the stimulation amplitude was tested in the range from 1 to 21 mA using the interconnected contacts of the stimulation array and the intra-anal anode, the impedance remained below 250 Ω and the system delivered 100% of the set current in all cases. Intra- anal sEMG showed an amplitude increase for current levels exceeding 6 mA. Conclusion: The system delivered stable electric current, which was proved by built-in impedance and current level measurements. Intra-anal sEMG confirmed the ability to target the branches of the autonomous nervous system originating from the sacral nerve roots. Significance: Stimulation outside of the operative field during rectal cancer surgery is feasible and may improve the practicality of pelvic intraoperative neuromonitoring. Index Terms—pelvic intraoperative neuromonitoring, autonomic nerve sparing, total mesorectal excision, extracorporeal stimulation, surface electromyography This paper was submitted for review on 11-07-2016. The * signifies the corresponding author. *Tomasz Moszkowski was with the Department of Biomedical Engineering, Fraunhofer Institut for Biomedical Engineering, St. Ingbert, Germany. He is now with the Department of Automatics and Biomedical Engineering, AGH – University of Science and Technology, Kraków, Poland, and with the Department of Research and Development at inomed Medizintechnik GmbH, Emmendingen, Germany (e-mail: tmoszkow@agh.edu.pl, t.moszkowski@inomed.com). Celine Wegner, Karin H. Somerlik-Fuchs, and Thilo B. Krüger are with the Department of Research and Development at inomed Medizintechnik GmbH, Emmendingen, Germany (e-mail: c.wegner@inomed.com). I. INTRODUCTION ERVE SPARING laparoscopic rectal cancer surgery aims to minimize postoperative neurogenic deficits, which may significantly improve the quality of life of rectal cancer patients. Difficult visual identification of the autonomous nerve structures and the need to monitor the nerve function motivate the use of neurophysiologic monitoring. Recently, neuromonitoring techniques have been used to predict urogenital and anorectal function, assess the functional nerve integrity, provide insight into the neuroanatomy of the pelvic floor, and increase the intraoperative identification rates of the neural structures [1], [2]. Nerve monitoring techniques have also been successfully implemented in robotic-assisted surgery for rectal cancer [3]. During pelvic intraoperative neuromonitoring (pIONM®), the surgeon introduces electric stimuli to the autonomous nerve structures of the pelvis minor via a handheld probe. Simultaneously, he observes changes in the electromyogram (EMG) of the internal and external anal sphincters (IAS and EAS) and in the intravesical pressure. In rectal cancer surgery, inserting a handheld probe for electric stimulation of the exposed autonomous nerves necessitates extending the surgical procedure and introduces time intervals during which unobserved nerve damage may occur. Similar challenges were faced during the monitoring of the somatic recurrent laryngeal nerve in thyroid surgery and various methods of stimulation were proposed. Permanent in- situ fixation of stimulation electrodes helped to identify real- time adverse changes of the evoked potential characteristics [4] Roman Ruff and Klaus-Peter Hoffmann are with the Department of Biomedical Engineering, Fraunhofer Institute for Biomedical Engineering, St. Ingbert, Germany (e-mail: roman.ruff@ibmt.fraunhofer.de, ). Daniel W. Kauff and Werner Kneist are with the Department of General, Visceral, and Transplant Surgery, University Medicine of the Johannes Gutenberg-University, Mainz, Germany (e-mail: daniel.kauff@unimedizin- mainz.de, werner.kneist@unimedizin-mainz.de). Piotr Augustyniak is with the Department of Automatics and Biomedical Engineering, AGH – University of Science and Technology, Kraków, Poland (e-mail: august@agh.edu.pl). Extracorporeal Stimulation of Sacral Nerve Roots for Observation of Pelvic Autonomic Nerve Integrity: Description of a Novel Methodological Setup Tomasz Moszkowski*, Daniel W. Kauff, Celine Wegner, Roman Ruff, Karin H. Somerlik-Fuchs, Thilo B. Krüger, Piotr Augustyniak, Member, IEEE , Klaus-Peter Hoffmann, Member, IEEE, Werner Kneist N