Technical aspects of a new approach to intraoperative pelvic neuromonitoring during robotic rectal surgery

It has been found that rectal surgery still leads to high rates of postoperative urinary, fecal, or sexual dysfunction, which is why nerve-sparing surgery has gained increasing importance. To improve functional outcomes, techniques to preserve pelvic autonomic nerves by identifying anatomic landmarks and implementing intraoperative neuromonitoring methods have been investigated. The objective of this study was to transfer a new approach to intraoperative pelvic neuromonitoring based on bioimpedance measurement to a clinical setting. Thirty patients (16 male, 14 female) involved in a prospective clinical investigation (German Clinical Trials Register DRKS00017437, date of first registration 31/03/2020) underwent nerve-sparing rectal surgery using a new approach to intraoperative pelvic neuromonitoring based on direct nerve stimulation and impedance measurement on target organs. Clinical feasibility of the method was outlined in 93.3% of the cases. Smooth muscle contraction of the urinary bladder and/ or the rectum in response to direct stimulation of innervating functional nerves correlated with a change in tissue impedance compared with the pre-contraction state. The mean amplitude (Amax) of positive signal responses was Amax = 3.8%, negative signal responses from a control tissue portion with no stimulation-induced impedance change had an amplitude variation of 0.4% on average. The amplitudes of positive and negative signal responses differed significantly (statistical analysis using two-sided t-test), allowing the nerves to be identified and preserved. The results indicate a reliable identification of pelvic autonomic nerves during rectal surgery.