Abstract
BackgroundDuring transurethral resection of bladder tumours (TURB), radio-frequency (RF) currents can lead to adverse neuromuscular stimulation (NMS). Here we present a novel ex vivo method to determine the risk of RF generators and their bipolar TURB modes to cause NMS. We aimed to develop an experimental platform for safety evaluation of new RF generators and their modes with a newly established test standard, suitable for replacement or reduction of animal testing.MethodsWe tested four contemporary RF generators with their bipolar modes for TURB in saline. A two-stage ex vivo approach was pursued: First, we recorded voltages at possible positions of the obturator nerve behind a porcine bladder wall in a TURB model using 18 RF applications per generator. Second, these voltage records were used as stimuli to evoke nerve compound action potentials (CAPs) in isolated porcine axillary nerves. The NMS potential was defined as the ratio between the observed area under the CAPs and the theoretical CAP area at maximum response and a firing rate of 250 Hz, which would reliably induce tetanic muscle responses in most human subjects. The measurement protocol was tailored to optimise reproducibility of the obtained NMS potentials and longevity of the nerve specimens.ResultsAs prerequisite for the clinical translation of our results, the robustness of our test method and reproducibility of the NMS potential are demonstrated with an excellent correlation (r = 0.93) between two sets of identical stimuli (n = 72 each) obtained from 16 nerve segments with similar diameters (4.2 ± 0.37 mm) in the nerve model. The RF generators differed significantly (p < 0.0001) regarding NMS potential (medians: 0–3%).ConclusionsOur test method is suitable for quantifying the NMS potential of different electrosurgical systems ex vivo with high selectivity at a reasonable degree of standardization and with justifiable effort. Our results suggest that the clinical incidence of NMS is considerably influenced by the type of RF generator. Future generations of RF generators take advantage from the proposed test standard through higher safety and less animal testing. Health professionals and treated patients will benefit most from improved RF surgery using generators with a low NMS risk.
Highlights
During transurethral resection of bladder tumours (TURB), radio-frequency (RF) currents can lead to adverse neuromuscular stimulation (NMS)
compound action potentials (CAP) in different phases of RF activation In a simplified view the activation of bipolar RF instruments in saline is characterised by two distinct phases: In the first phase the ignition of a spark is triggered by relatively high current flow and during the second phase, where cutting takes place, the spark is sustained at a relatively lower current flow
We found significant differences in NMS potentials (Fig. 4) between the four commercial RF generators (Kruskal-Wallis test p < 0.0001) with medians between 0% (RF generator A) and ~ 3% (RF generator D) (Table 1)
Summary
During transurethral resection of bladder tumours (TURB), radio-frequency (RF) currents can lead to adverse neuromuscular stimulation (NMS). Potential intraoperative complications of TURB include bleeding and bladder perforation, typically as a consequence of stimulation of the obturator nerve, which may be associated with sudden, strong contractions of leg adductors. These contractions can lead to uncontrolled movements of the instruments introduced into the bladder, possibly leading to a bladder perforation, which requires conversion to open surgery. Current in vivo or clinical techniques for evaluating NMS typically include documenting the incidence of adverse NMS events such as obturator nerve reflex/adductor muscle contraction or bladder injury/perforation rate [2, 3, 5, 8, 9]. This was previously only possible with in vivo animal testing or clinical trials
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