Online signal processing of internal anal sphincter activity during pelvic autonomic nerve stimulation: a new method to improve the reliability of intra-operative neuromonitoring signals

Automatic muscle impedance and nerve analyzer (AMINA) as a novel approach for classifying bioimpedance signals in intraoperative pelvic neuromonitoring

Frequent complications arising from low anterior resections include urinary and fecal incontinence, as well as sexual disorders, which are commonly associated with damage to the pelvic autonomic nerves during surgery. To assist the surgeon in preserving pelvic autonomic nerves, a novel approach for intraoperative pelvic neuromonitoring was investigated that is based on impedance measurements of the innervated organs. The objective of this work was to develop an algorithm called AMINA to classify the bioimpedance signals, with the goal of facilitating signal interpretation for the surgeon. Thirty patients included in a clinical investigation underwent nerve-preserving robotic rectal surgery using intraoperative pelvic neuromonitoring. Contraction of the urinary bladder and/or rectum, triggered by direct stimulation of the innervating nerves, resulted in a change in tissue impedance signal, allowing the nerves to be identified and preserved. Impedance signal characteristics in the time domain and the time-frequency domain were calculated and classified to develop the AMINA. Stimulation-induced positive impedance changes were statistically significantly different from negative stimulation responses by the percent amplitude of impedance change Amax in the time domain. Positive impedance changes and artifacts were distinguished by classifying wavelet scales resulting from peak detection in the continuous wavelet transform scalogram, which allowed implementation of a decision tree underlying the AMINA. The sensitivity of the software-based signal evaluation by the AMINA was 96.3%, whereas its specificity was 91.2%. This approach streamlines and automates the interpretation of impedance signals during intraoperative pelvic neuromonitoring.

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.

Low Anterior Resection Syndrome (LARS) after Surgery for Rectal Cancer: An Inevitable Price to Pay for Survival, or a Preventable Complication?

BACKGROUND

Rectal cancer is frequent and often treated with sphincter-saving procedures that may cause LARS, a syndrome characterized by symptoms of bowel disfunction that may severely affect quality of life. LARS is common, but its pathogenesis is mostly unknown. The aim of this study is to assess the incidence of LARS and to identify potential risk factors.

METHODS

We performed an observational retrospective single center analysis. The following data were collected and analyzed for each patient: demographics, tumor-related data, and intra- and peri-operative data. Statistical analysis was conducted, including descriptive statistics and multivariate logistic regression to identify independent risk factors.

RESULTS

Total LARS incidence was 31%. Statistically significant differences were found in tumor distance from anal verge, tumor extension (pT and diameter) and tumor grading (G). Multivariate analysis identified tumor distance from anal verge and tumor extension as an independent predictive factor for both major and total LARS. Adjuvant therapy, although not significant at univariate analysis, was identified as an independent predictive factor. Time to stoma closure within 10 weeks seems to reduce incidence of major LARS.

CONCLUSIONS

bold LARS affects a considerable portion of patients. This study identified potential predictive factors that could be useful to identify high risk patients for LARS.

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

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.

Intraoperative neuromonitoring in rectal cancer surgery: a systematic review and meta-analysis

PURPOSE

The aim of this study is to evaluate the role of pelvic intraoperative neuromonitoring (pIONM) in rectal cancer surgery.

METHODS

A systematic review of the literature and a meta-analysis were conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and the Cochrane Handbook for Systematic Reviews of Interventions.

RESULTS

Overall, nine studies were identified. Quantitative analysis was performed only in three trials. Bilateral pIONM improved postoperative anorectal and urogenital functional outcomes. However, unilateral pIONM displayed a significant effect only on erectile function (p = 0.001).

CONCLUSIONS

Our findings suggest a positive effect of pIONM on postoperative functional outcomes and quality of life after rectal cancer surgery. Due to several limitations, further trials are required in order to elucidate the exact role of pIONM.

Extracorporeal Stimulation of Sacral Nerve Roots for Observation of Pelvic Autonomic Nerve Integrity: Description of a Novel Methodological Setup

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.

Postprocessing algorithm for automated analysis of pelvic intraoperative neuromonitoring signals

Two dimensional pelvic intraoperative neuromonitoring (pIONM®) is based on electric stimulation of autonomic nerves under observation of electromyography of internal anal sphincter (IAS) and manometry of urinary bladder. The method provides nerve identification and verification of its’ functional integrity. Currently pIONM® is gaining increased attention in times where preservation of function is becoming more and more important. Ongoing technical and methodological developments in experimental and clinical settings require further analysis of the obtained signals. This work describes a postprocessing algorithm for pIONM® signals, developed for automated analysis of huge amount of recorded data. The analysis routine includes a graphical representation of the recorded signals in the time and frequency domain, as well as a quantitative evaluation by means of features calculated from the time and frequency domain. The produced plots are summarized automatically in a PowerPoint presentation. The calculated features are filled into a standardized Excel-sheet, ready for statistical analysis.

Surface Electromyography Reliably Records Electrophysiologically Evoked Internal Anal Sphincter Activity: A More Minimally Invasive Approach for Monitoring Extrinsic Innervation

BACKGROUND

Even in the case of minimally invasive pelvic surgery, sparing of the autonomic nerve supply is a prerequisite for maintaining anal sphincter function. Internal anal sphincter (IAS) innervation could be electrophysiologically identified based on processed electromyographic (EMG) recordings with conventional bipolar needle electrodes (NE). This experimental study aimed for the development of a minimally invasive approach via intra-anal surface EMG for recordings of evoked IAS activity.

METHODS

Six male pigs underwent nerve-sparing low anterior rectal resection. Electric autonomic nerve stimulations were performed under online-processed EMG of the IAS. EMG recordings were simultaneously carried out with conventional bipolar NE as the reference method and newly developed intra-anal surface electrodes (SE) in different designs.

RESULTS

In all experiments, the IAS activity could be continuously visualized via EMG recordings based on NE and SE. The median number of bipolar electric stimulations per animal was 27 (range 5-52). The neurostimulations resulted in significant EMG amplitude increases for both recording types [NE: median 3.0 µV (interquartile range, IQR 2.8-3.5) before stimulation vs. 7.1 µV (IQR 3.9-13.8) during stimulation, p < 0.001; SE: median 3.6 µV (IQR 3.1-4.3) before stimulation vs. 6.8 µV (IQR 4.8-10.3) during stimulation, p < 0.001].

CONCLUSIONS

Intra-anal SE enabled reliable EMG of electrophysiologically evoked IAS activity similar to the conventional recording via NE. The transfer of the method to access platforms for transanal total mesorectal excision or robotics may offer a practical more minimally invasive approach for monitoring extrinsic innervation.

Effect of intra-operative autonomic nerve stimulation on pelvic nerve preservation during radical laparoscopic proctectomy

AIM

This study assessed the effect of intra-operative electrical nerve stimulation (INS) on pelvic autonomic nerve preservation (PANP) during laparoscopic resection for rectal cancer.

METHOD

A total of 189 consecutive cases of radical laparoscopic proctectomy were included. PANP was assessed visually or with INS. Urinary function was evaluated by residual urine volume (RUV), International Prostatic Symptom Score (IPSS) and recatheterization rate. Erectile function was evaluated using the International Index of Erectile Function (IIEF-5) scale.

RESULTS

INS successfully confirmed PANP in 65 (91.5%) patients, while direct vision confirmed PANP in only 72 (61.0%) patients. Compared with the successfully confirmed patients, failed patients in the INS group exhibited higher postoperative RUV (100.0 ± 34.6 vs 25.2 ± 13.6 ml, P = 0.003), higher IPSS (7 days, 20.0 ± 8.6 vs 6.5 ± 2.4, P = 0.012; 1 month, 13.5 ± 6.0 vs 5.3 ± 1.9, P = 0.020; 6 months, 11.7 ± 5.1 vs 4.5 ± 1.7, P = 0.018), a greater number of incidences of a micturition disorder (66.7% vs 1.5%, P = 0.000), higher recatheterization rates (33.3% vs 1.5%, P = 0.017) and a lower IIEF score at 3 months (8.25 ± 0.96 vs 10.93 ± 1.99, P = 0.012) and 6 months (12.50 ± 1.29 vs 15.63 ± 1.65, P = 0.001) postoperatively. Compared with the vision group, the INS group had less deterioration in postoperative RUV (31.5 ± 26.4 vs 54.0 ± 46.7 ml, P = 0.000), lower IPSS (7 days, 7.7 ± 5.0 vs 11.0 ± 6.6, P = 0.000; 1 month, 6.0 ± 3.3 vs 7.6 ± 5.4, P = 0.012) and higher IIEF score (3 months, 10.69 ± 2.07 vs 9.42 ± 2.05, P = 0.001; 6 months, 15.36 ± 1.85 vs 13.64 ± 2.00, P = 0.000) as well as a lower incidence of urination disorders (7.0% vs 17.8%, P = 0.038).

CONCLUSION

INS is effective for the accurate evaluation of PANP during radical laparoscopic proctectomy. Combined with INS, laparoscopic proctectomy is more effective in urogenital function protection.

Impact of inhalation vs. intravenous anaesthesia on autonomic nerves and internal anal sphincter tone

BACKGROUND

Pelvic intraoperative neuromonitoring (pIONM) aims to identify and spare the autonomic nerves and maintain patients' quality of life. The effect of anaesthetic agents on the pIONM signal is unknown; therefore, the aim of the present study was to compare the influences of inhalation anaesthesia (IA) and total intravenous anaesthesia (TIVA).

METHODS

Twenty rectal cancer patients undergoing open nerve-sparing total mesorectal excision (TME) were assigned to pIONM under either IA or TIVA (n = 10 per group). IA was maintained with sevoflurane and TIVA with propofol. During surgery, pelvic autonomic nerves were electrically stimulated under electromyography (EMG) of the internal anal sphincter (IAS). These triggered EMG signals were analysed.

RESULTS

The absolute EMG amplitude during pIONM increased to 1.20 μV (interquartile range (IQR): 0.94-1.6) for IA and 1.49 μV (IQR: 0.84-2.75) for TIVA (P = 0.002). The relative EMG amplitude increase also was significantly lower for IA (0.59; IQR: 0.30-0.81; TIVA: 0.99; IQR: 0.62-2.5), (P = 0.001).

CONCLUSIONS

This is the first study to compare the influences of IA and TIVA on the autonomic nervous system. While both anaesthetic regimens proved useful for pIONM, TIVA with propofol may provide better signal quality than IA with sevoflurane.

Percutaneous nerve evaluation based on electrode placement under control of autonomic innervation

BACKGROUND

Foramen needle electrode placement for percutaneous nerve evaluation (PNE) is currently carried out while observing the somatic motor response. This study investigated electrode placement while observing the autonomic as well as the somatic response.

METHODS

A consecutive series of ten patients (seven women) with a median age of 51.9 (range 30-75) years undergoing PNE for faecal incontinence (n = 6) and obstipation (n = 4) were investigated prospectively. Electrode placement was carried out under simultaneous electromyography (EMG) of the external anal sphincter (EAS) and internal anal sphincter (IAS) and cystomanometry.

RESULTS

PNE under control of somatic and autonomic nerve responses was carried out in all patients. In three out of ten patients, initial needle electrode placement showed single evoked EMG signals from the EAS. Final electrode placement resulted in adequate somatic motor and autonomic responses in all patients. Comparison of the increases in IAS EMG amplitude on the right and left stimulation sites for sacral nerves S3 and S4 demonstrated significant differences [S3 right: median 15.3 (interquartile range (IQR) 10.4; 20.1) µV vs. S3 left: median 11.6 (IQR 8.6; 16.0) µV, p = 0.034 and S4 right: median 24.1 (IQR 20.1; 37.2) µV vs. S4 left: median 12.0 (IQR 10.7; 13.7) µV, p = 0.012]. Stimulation-induced bladder activation was achieved in all seven patients with concomitant urinary dysfunction.

CONCLUSIONS

Control of not just the somatic motor response but also the autonomic nerve response during foramen needle electrode placement may objectify PNE.

Clinical value of pelvic autonomic nerve preservation during laparoscopic surgery for low rectal cancer

AIM: To observe the function of pelvic autonomic nerve preservation (PANP) during laparoscopic surgery for low rectal cancer.

METHODS: Seventy-six elderly patients who underwent laparoscopic surgery for low rectal cancer were included in this study. These patients were divided into either an observation group (n = 40) or a control group (n = 36). The observation group underwent PANP, while the control group did not undergo PANP. After treatment, the short-term and long-term micturition function was observed. In addition, a three-year follow-up was performed, and the quality of life was scored at the last follow-up.

RESULTS: The percentage of patients who had improved short-term and long-term micturition function was significantly higher in the observation group than in the control group (17.50% vs 47.22%, 0% vs 5.56%, both P < 0.05). Psychological state (SAS, SDS) and self esteem (SES) scores were significantly better in the observation group than in the control group (36.64 ± 4.27 vs 42.37 ± 4.35, 32.84 ± 3.21 vs 39.43 ± 3.92, 24.45 ± 4.20 vs 18.54 ± 3.20, all P < 0.01).

CONCLUSION: PANP during laparoscopic surgery for low rectal cancer can improve micturition function and patient's quality of life.

Laparoscopic neuromapping in pelvic surgery: scopes of application

BACKGROUND

New developments in intraoperative electrophysiological neuromonitoring for conventional surgery are providing further insights into functional neuroanatomy and nerve-sparing in the minor pelvis. The aim of this study was to open up potential scopes of application in laparoscopy.

METHODS

Ten patients with different indications for surgery (presacral tumor excision, n = 2; resection rectopexy. n = 2; low anterior rectal resection, n = 2; proctocolectomy. n = 2; abdomino-perineal excision of the rectum, n = 2) were investigated prospectively. The pelvic autonomic nerves were bilaterally mapped by laparoscopic electric stimulation under simultaneous electromyography of the internal anal sphincter and manometry of the bladder. Stimulation results were compared to patients' anorectal and urogenital functional outcome.

RESULTS

In all the operations laparoscopic neuromapping (LNM) was technically feasible. Laparoscopy enabled excellent visibility of pelvic neural structures for simple and differentiated electric stimulation. In all cases LNM resulted in significantly evoked electromyographic potentials and intravesical pressure rises. The technique facilitated electrophysiological determination of functional neuroanatomical topography in the minor pelvis. The stimulation results were suitable to confirm laparoscopic nerve-sparing and compatible with patients' anorectal and urogenital functional outcome.

CONCLUSIONS

LNM is technically feasible and opens up a new dimension for verification of functional nerve integrity. Further developments and investigations are mandatory to evaluate its role for laparoscopic nerve-sparing procedures.

Total mesorectal excision--does the choice of dissection technique have an impact on pelvic autonomic nerve preservation?

BACKGROUND

The aim of this experimental study was to assess the quality of pelvic autonomic nerve preservation of different dissection techniques.

MATERIAL AND METHODS

Twelve pigs underwent low anterior rectal resection (LARR) with scissors, ultracision, monopolar diathermy, and waterjet, each in three animals. Assessment of pelvic autonomic nerve preservation was carried out by stimulation of the pelvic splanchnic nerves under electromyography of the internal anal sphincter (IAS). Neurostimulation was performed bilaterally after posterior dissection, after complete mesorectal dissection, and after rectal resection.

RESULTS

Stimulation resulted in significantly increased amplitudes of the time-based electromyographic signal of the IAS, confirming nerve preservation. The stimulation results after complete mesorectal dissection showed comparable median amplitude increases for dissection with scissors (10.34 μV (interquartile range [IQR], 5.58; 14.74)) and ultracision (9.79 μV (IQR, 7.63; 11.6)). Lower amplitude increases were observed for monopolar diathermy (4.47 μV (IQR, 2.52; 10.46)) and waterjet (0.61 μV (IQR, 0.07; 2.11)) (p = 0.038). All animals undergoing dissection with scissors, ultracision, and monopolar diathermy had bilateral positive results. Of three animals undergoing LARR with waterjet, one had bilateral positive results. Two had unilateral negative results, indicating incomplete nerve preservation.

CONCLUSION

Scissors, ultracision, and monopolar diathermy might have comparable nerve-sparing potentials and differed from waterjet.

Continuous intraoperative monitoring of autonomic nerves during low anterior rectal resection: an innovative approach for observation of functional nerve integrity in pelvic surgery

PURPOSE

The aim of this study was to develop a methodological setup for continuous intraoperative neuromonitoring with intent to improve nerve-sparing pelvic surgery.

METHODS

Fourteen pigs underwent low anterior rectal resection. Continuous stimulation of pelvic autonomic nerves was carried out with a newly developed tripolar surface electrode during lateral, anterolateral, and anterior mesorectal dissection. Neuromonitoring was performed under electromyography of the autonomic innervated internal anal sphincter.

RESULTS

Continuous neuromonitoring resulted in significantly increased electromyographic amplitudes of the internal anal sphincter, confirming intact innervation throughout the whole dissection in each animal (median 0.9 μV, interquartile range 0.5; 1.5 vs. median 3.4 μV, interquartile range 2.1; 4.7) (p < 0.001). The median dissection time in each animal was 10 min within a median number of ten (range 8-13) tripolar electric stimulations.

CONCLUSION

The present study is the first to demonstrate that continuous intraoperative monitoring of pelvic autonomic nerves during low anterior rectal resection is feasible.

Total mesorectal excision with intraoperative assessment of internal anal sphincter innervation provides new insights into neurogenic incontinence

BACKGROUND

The aim of this prospective study was to assess internal anal sphincter (IAS) innervation in patients undergoing total mesorectal excision (TME) by intraoperative neuromonitoring (IONM).

STUDY DESIGN

Fourteen patients underwent TME. IONM was carried out through pelvic splanchnic nerve stimulation under continuous electromyography of the IAS. Anorectal function was assessed with the digital rectal examination scoring system and a standardized questionnaire.

RESULTS

Nine of 11 patients who underwent low anterior resection had positive IONM results, with stimulation-induced increased IAS electromyographic amplitudes (median 0.23 μV (interquartile range [IQR] 0.05, 0.56) vs median 0.89 μV (IQR 0.64, 1.88), p < 0.001) after TME. The patients with the positive IONM results were continent after stoma closure. Of 2 patients with negative IONM results, 1 had fecal incontinence after closure of the defunctioning stoma and received a permanent sigmoidostomy. In the other patient the defunctioning stoma was deemed permanent due to decreased anal sphincter function. In 3 patients who underwent abdominoperineal excision, IONM assessed denervation of the IAS after performance of the abdominal part.

CONCLUSIONS

This study demonstrated that IONM of IAS innervation in rectal cancer patients is feasible and may predict neurogenic fecal incontinence.