A new method of intraoperative pelvic neuromonitoring: a preclinical feasibility study in a porcine model

Abstract

Low anterior resections (LAR) are frequently associated with complications such as urinary and fecal incontinence as well as sexual disorders. Typical risk factors are rectal cancer with low tumor location, preoperative radiotherapy, and surgery-related damage of pelvic autonomic nerves. As preserving the pelvic autonomic nerves without any technical assistance is challenging, the objective of this preclinical study was to investigate the technical feasibility of a new method for intraoperative pelvic neuromonitoring. Twelve female pigs undergoing low anterior resections were involved in a prospective preclinical study. Intraoperative pelvic neuromonitoring included direct pelvic nerve stimulation and tissue impedance measurement on the urinary bladder and the rectum for the identification of efferent pelvic nerves in the surgical area. Immunohistochemistry was used to verify the results. Smooth muscle contraction of the urinary bladder and/or the rectum in response to direct stimulation of the innervating nerves was detectable with impedance measurement. The macroscopic contraction of both the urinary bladder and the rectum correlated with a change in tissue impedance compared to the status before contraction. Thus, it was possible to identify pelvic nerves in the surgical area, which allows the nerves to be preserved. The results indicate a reliable identification of pelvic autonomic nerves, which allows nerve damage to be prevented in the future.

Pelvic Intraoperative Neuromonitoring Prevents Dysfunction in Patients With Rectal Cancer

“…6,7 Impedance measurement in target muscles seems suitable, at least, but needs further investigation in clinical studies. 21 The pIONM system we used had overall accuracies of 88% and 90% for predicting sexual function in open and laparoscopic TME surgery, respectively. The pIONM device showed even higher accuracy in predicting postoperative urinary and ano-(neo-) rectal function.…”

“…Alternatives to pIONM were not considered because intrarectal manometry20 was impractical and penile tumescence evaluation, measured with a strain-gauge transducer, cannot be performed in women and did not appear to be sufficiently accurate in rectal surgery 6,7. Impedance measurement in target muscles seems suitable, at least, but needs further investigation in clinical studies 21…”

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

“…By means of analog-to-digital conversion (ADC) the resulting direct current (DC) signal is converted to an output signal U(t), which represents a processed voltage drop. This processed voltage drop U(t) is displayed on the neuromonitor as a function of time, proportional to the target organs’ tissue impedance 17 . The application software of the neuromonitoring system stores the recorded raw data (processed voltage drop across the tissue U(t)) and the stimulation parameters in TDMS files (Technical Data Management Streaming, file format by National Instruments Corporation, Austin, USA) with a sampling rate of 10 Hz.…”

“…Spikes are triggered when physiologically spontaneous rhythmic changes of the membrane potential exceed a threshold potential, which leads to a slow contraction of the smooth muscle for several seconds 15 , 16 . This slow contraction of the smooth muscle occurs in the scope of intraoperative neuromonitoring after applying stimulation pulses to nerve tissue 17 , 18 .…”

“…A change in tissue impedance on the bladder and/ or the rectum compared to the status before nerve stimulation is rated as an indicator of smooth muscle contraction and therefore identification of functional nerves. The technical feasibility of the method was proven in a preclinical animal study with twelve female pigs 17 .…”