Spectral analysis interpretation of electrosurgical generator nerve and muscle stimulation

Challenges in creating dissectible anatomical 3D prints for surgical teaching

Three-dimensional (3D) printing, or additive manufacturing, is now a widely used tool in pre-operative planning, surgical teaching and simulator training. However, 3D printing technology that produces models with accurate haptic feedback, biomechanics and visuals for the training surgeon is not currently available. Challenges and opportunities in creating such surgical models will be discussed in this review paper. Surgery requires proper tissue handling as well as knowledge of relevant anatomy. To prepare doctors properly, training models need to take into account the biomechanical properties of the anatomical structures that will be manipulated in any given operation. This review summarises and evaluates the current biomechanical literature as it relates to human tissues and correlates the impact of this knowledge on developing high fidelity 3D printed surgical training models. We conclude that, currently, a printer technology has not yet been developed which can replicate many of the critical qualities of human tissue. Advances in 3D printing technology will be required to allow the printing of multi-material products to achieve the mechanical properties required.

Histological and finite element analysis of cell death due to irreversible electroporation

Irreversible electroporation (IRE) has been shown to be an effective method of killing cells locally. In contrast to radiofrequency ablation, the mechanism by which cells are thought to die via IRE is the creation of pores in cell membranes, without substantial increase in tissue temperature. To determine the degree to which cell death is non-thermal, we evaluated IRE in porcine hepatocytes in vivo. Using pulse widths of 10μs, bursts of 3 kV square-wave pulses were applied through a custom probe to the liver of an anesthetized pig. Affected tissue was evaluated histologically via stainings of hematoxylin & eosin (H&E), nitroblue tetrazolium (NBT) to monitor cell respiration and TUNEL to gauge apoptosis. Temperature was measured during the application of electroporation, and heat transfer was modeled via finite element analysis. Cell death was calculated via Arrhenius kinetics. Four distinct zones were observed within the ring return electrode; heat-fixed tissue, coagulation, necrotic, and viable. The Arrhenius damage integral estimated complete cell death only in the first zone, where the temperature exceeded 70°C, and partial or no cell death in the other zones, where maximum temperature was approximately 45°C. Except for a limited area near the electrode tip, cell death in IRE is predominantly due to a non-thermal mechanism.

A true to life simulation of electrosurgery

A laboratory simulation has been devised for use in developing and testing physiologic monitoring systems' performance in the presence of electrosurgical interference. This facilitated the development through iterative optimization of an EEG based parameter whose performance is improved during electrosurgery. The system was found to have an improvement of 94% in response to electrosurgery interference in the laboratory simulation. It was found to be improved 78% from all interference sources when tested clinically during actual surgery. This demonstrates the efficacy of the simulation.

Electrical nerve and muscle stimulation by radio frequency surgery: role of direct current loops around the active electrode

Tissue cutting by electrosurgery is often accompanied with stimulation of nerves and muscles, despite the high frequency of the alternating current being applied. The main source of this stimulation is thought to be the generation of low frequency current by the nonlinear sparking process. However, measurement of this low-frequency current, in the generator electrode's circuit, showed relatively small values, barely sufficient to support this hypothesis. In this study more powerful low frequency current could be identified, indeed also originating from the nonlinear sparking process. Local direct and low frequency currents, at a level of tens of milliamperes, appeared to be generated between different sites of the active electrode-tissue interface. Probably these local currents have not been noticed before as they cannot be detected in the outer chain of generator, electrodes, and connecting wires. This finding may explain why most measures, intended to prevent stimulation by modifying this outer chain, had only limited success.