Multifunctional surface probe for less invasive stimulation of sacral somatic and autonomic outflow under EMG feedback control

Invasive electric stimulation of sacral somatic and autonomic outflow is used for treatment of urinary and anorectal functional disturbances and selective monitoring of the autonomic nerve-sparing technique in pelvic surgery, the so called pelvic intraoperative neuromonitoring. The aim of this experimental study was to investigate a less invasive approach for simultaneous stimulation of sacral somatic and autonomic outflow and concomitant recording of feedback.A newly developed multifunctional surface probe for simultaneous transrectal stimulation and electromyography (EMG) of external (EAS) and internal anal sphincter (IAS) was investigated in a consecutive series of six male pigs. The probe (cathode) was designed for intra-anal/-rectal application. An additional surface anode was placed on the animals´ back at the level of the sacrum. Each animal underwent autonomic nerve-sparing low anterior rectal resection. The transrectal stimulations followed a standardized protocol. Further direct stimulation of the surgically exposed pelvic autonomic nerves was carried out with a hand-guided bipolar microfork probe.In all six experiments, the transrectal stimulation resulted in significantly increased EMG signals of the somatically innervated EAS (21.0 μV (interquartile range (IQR): 17.8; 64.4) before stimulation vs. 375.8 μV (IQR: 103.4; 895.9) during stimulation, p = 0.004) and autonomically innervated IAS (35.1 μV (IQR: 27.9; 41.7) before stimulation vs. 1115.7 μV (IQR: 420.1; 2920.3) during stimulation, p = 0.008). Subgroup analysis of the observed IAS EMG signals under transrectal stimulation and hand guided direct stimulation revealed no significant differences between both methods (70.5 μV (IQR: 31.5; 322.7) vs. 320.3 μV (IQR: 204.0; 358.0), p = 0.109).The newly developed multifunctional surface probe enabled successful transrectal stimulation of sacral somatic and autonomic outflow under EMG feedback control. The clinical value of this less invasive approach for the treatment of functional disturbances needs further investigations.