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ObjectiveDuring nerve-sparing robot-assisted radical prostatectomy (RARP) bipolar electrocoagulation is often used but its use is controversial for the possible thermal damage of neurovascular bundles. Aim of the study was to evaluate the spatial-temporal thermal distribution in the tissue and the correlation with the electrosurgery-induced tissue damage in a controlled, CO2-rich environment modelling the laparoscopy conditions..MethodsWe manufactured a sealed plexiglass chamber (SPC) equipped with sensors to reproduce experimentally the environmental conditions of pneumoperitoneum during RARP. We evaluated in 64 pig musculofascial tissues (PMTs) of approximately 3 cm3 × 3 cm3 × 2 cm3 the spatial-temporal thermal distribution in the tissue and the correlation with the electrosurgery-induced tissue damage in a controlled CO2-rich environment modeling the laparoscopy conditions. Critical heat spread of bipolar cauterizing during surgical procedure was assessed by the employment of a compact thermal camera (C2) with a small core sensor (60 × 80 microbolometer array in the range 7–14 μm).ResultsBipolar instruments used at 30 W showed a thermal spread area of 18 mm2 when applied for 2 s and 28 mm2 when applied for 4 s. At 60 W, bipolar instruments showed a mean thermal spread and 19 mm2 when applied for 2 s; and 21 mm2 when applied for 4 s. Finally, histopathological analysis showed that thermal damage is distributed predominantly on the surface rather than in depth.ConclusionsThe application of these results is very interesting for the definition of an accurate use of bipolar cautery during nerve-sparing RARP. It demonstrates the feasibility of using miniaturized thermal sensors, thus addressing the potential for next developments regarding the design of thermal endoscopic devices for robotic use.

Multi-spectral imaging systems, namely thermal and visible spectrum imaging systems, are recently being employed successfully in multiple civilian applications, such as civil engineering , precision agriculture, and cultural heritage preservation [1], due to the more general availability of high-performing, compact sen- sors. The same success can not yet be appreciated in medical or surgical applications, with most examples of thermography in medicine being applied on the epidermis [2] or specialized applications with limited measurements [3]. Nevertheless, direct thermal tissue measurements could prove invaluable in laparoscopy and laparo-assisted robotic surgery, where bipolar electroco- agulation or ultrasonic energy are often used to achieve haemostasis to maximise a clear view of the surgical field. The temperatures exceed 45 ◦ C where disruption in the neurovascular bundles (NVB) functions was observed in vivo , with protein denaturation and subsequent cellular death occurring between 57 ◦ C and 65 ◦ C [4]. Coagulation by thermal energy can be considered responsible for the damage to the NVB that are intimately located on the lateral, posterolateral and posterior surface of the prostate during nerve-sparing robotic-assisted radical prostatec- tomy (RARP) [5]. This damage can decrease the chance of a full recovery of physiological functions after the procedure, namely the erection and urinary continence, which is estimated to be at 50% [6]. For this reason, cautery-free procedures have been evaluated to reduce the amount of induced thermal damage by using clips [7], but they introduce risk of unintentional neural bundle dissection. We present a novel endoscope prototype for minimal invasive surgery: it integrates full stereoscopic vision with 3D-mapped, direct thermal measurements to evaluate the heat propagation over the surface target tissue during bipolar coagulation. The precise mapping of the multi-spectral images would allow clinicians to quickly assess the risk of damage to sensitive tissues intra- operatively.