Ana Serrano González

Research and development of a new RF-assisted device for bloodless rapid transection of the liver: Computational modeling and in vivo experiments

BackgroundEfficient and safe transection of biological tissue in liver surgery is strongly dependent on the ability to address both parenchymal division and hemostasis simultaneously. In addition to the conventional clamp crushing or finger fracture methods other techniques based on radiofrequency (RF) currents have been extensively employed to reduce intraoperative blood loss. In this paper we present our broad research plan for a new RF-assisted device for bloodless, rapid resection of the liver.MethodsOur research plan includes computer modeling and in vivo studies. Computer modeling was based on the Finite Element Method (FEM) and allowed us to estimate the distribution of electrical power deposited in the tissue, along with assessing the effect of the characteristics of the device on the temperature profiles. Studies based on in vivo pig liver models provided a comparison of the performance of the new device with other techniques (saline-linked technology) currently employed in clinical practice. Finally, the plan includes a pilot clinical trial, in which both the new device and the accessory equipment are seen to comply with all safety requirements.ResultsThe FEM results showed a high electrical gradient around the tip of the blade, responsible for the maximal increase of temperature at that point, where temperature reached 100°C in only 3.85 s. Other hot points with lower temperatures were located at the proximal edge of the device. Additional simulations with an electrically insulated blade produced more uniform and larger lesions (assessed as the 55°C isotherm) than the electrically conducting blade. The in vivo study, in turn, showed greater transection speed (3 ± 0 and 3 ± 1 cm2/min for the new device in the open and laparoscopic approaches respectively) and also lower blood loss (70 ± 74 and 26 ± 34 mL) during transection of the liver, as compared to saline-linked technology (2 ± 1 cm2/min with P = 0.002, and 527 ± 273 mL with P = 0.001).ConclusionA new RF-assisted device for bloodless, rapid liver resection was designed, built and tested. The results demonstrate the potential advantages of this device over others currently employed.

RF tumor ablation with internally cooled electrodes and saline infusion: what is the optimal location of the saline infusion?

BackgroundRadiofrequency ablation (RFA) of tumors by means of internally cooled electrodes (ICE) combined with interstitial infusion of saline may improve clinical results. To date, infusion has been conducted through outlets placed on the surface of the cooled electrode. However, the effect of infusion at a distance from the electrode surface is unknown. Our aim was to assess the effect of perfusion distance (PD) on the coagulation geometry and deposited power during RFA using ICE.MethodsExperiments were performed on excised bovine livers. Perfusion distance (PD) was defined as the shortest distance between the infusion outlet and the surface of the ICE. We considered three values of PD: 0, 2 and 4 mm. Two sets of experiments were considered: 1) 15 ablations of 10 minutes (n ≥ 4 for each PD), in order to evaluate the effect of PD on volume and diameters of coagulation; and 2) 20 additional ablations of 20 minutes. The effect of PD on deposited power and relative frequency of uncontrolled impedance rises (roll-off) was evaluated using the results from the two sets of experiments (n ≥ 7 for each PD). Comparisons between PD were performed by analysis of variance or Kruskal-Wallis test. Additionally, non-linear regression models were performed to elucidate the best PD in terms of coagulation volume and diameter, and the occurrence of uncontrolled impedance rises.ResultsThe best-fit least square functions were always obtained with quadratic curves where volume and diameters of coagulation were maximum for a PD of 2 mm. A thirty per cent increase in volume coagulation was observed for this PD value compared to other values (P < 0.05). Likewise, the short coagulation diameter was nearly twenty five per cent larger for a 2 mm PD than for 0 mm. Regarding deposited power, the best-fit least square function was obtained by a quadratic curve with a 2 mm PD peak. This matched well with the higher relative frequency of uncontrolled impedance rises for PD of 0 and 4 mm.ConclusionSaline perfusion at around 2 mm from the electrode surface while using an ICE in RFA improves deposition of energy and enlarges coagulation volume.

Electrical-thermal performance of a cooled RF applicator for hepatic ablation with additional distant infusion of hypertonic saline: in vivo study and preliminary computer modeling.

Purpose: The Cool-tip electrode is one of the most widely employed applicators in radiofrequency (RF) hepatic ablation. Previous research demonstrated that it is possible to enlarge coagulation volume when the single cooled electrode is associated with distant infusion of saline (hybrid applicator). The aim of this study was to compare the electrical-thermal behaviour of the Cool-tip electrode with that of the hybrid applicator. Materials and methods: Forty-two RF ablations were performed on a total of 10 pigs: 22 with the Cool-tip electrode and 20 with the hybrid applicator (low infused saline volumetric flow rate of 6 mL/h at 2 mm distance). We compared both electrical performance (delivered power and number of roll-offs, i.e. sudden rises in impedance that interrupt the power delivery) and coagulation zone characteristics. In addition, we built a one-dimensional model to provide a basic physical explanation of the difference in performance between the different applicators. Results: The experimental results showed that the number of roll-offs with the Cool-tip electrode was higher (24.3 ± 3.1 versus 6.7 ± 7.0). The hybrid applicator created larger coagulation volumes (19.7 ± 9.5 cm3 versus 9.5 ± 5.8 cm3) with larger transverse diameters (2.5 ± 0.6 versus 1.9 ± 0.5 cm). The one-dimensional model confirmed the delay in the incidence of the first roll-off, but not the heterogeneity of the hybrid applicators electrical performance in the experiments. Conclusions: The hybrid applicator produces fewer roll-off episodes than the Cool-tip electrode and creates larger coagulation volumes with larger transverse diameters.

Single Instrument for Hemostatic Control in Laparoscopic Partial Nephrectomy in a Porcine Model Without Renal Vascular Clamping

PURPOSE To test the viability of a new device to obtain hemostasis during laparoscopic partial nephrectomy (LPN) without vascular clamping. MATERIALS AND METHODS We performed a comparative experimental study between a new radiofrequency (RF)-assisted device consisting of a handheld instrument that simultaneously conducts coagulation and cutting tasks without hilar clamping vs a standard technique with hilar clamping. A porcine model was used (10 animals per group) with survival of 17 days. RESULTS The estimated blood loss with the new device was significantly lower than with the standard technique (15.5±23.7 vs 79.4±76.3  mL). Although transection time was longer with the new device (10.7±13.7 vs 2.1±1.2  min), the total operative time was significantly shorter (35.3±13.7 vs 60.2±10.5  min). Evidence of localized urinary extravasation (urinoma) was identical in both groups (five cases). The group subjected to the new device, however, showed a significantly higher number of cases of leakage after conducting the methylene-blue test: eight (80%) cases vs only one (11%) with the standard technique. Necrosis depth was significantly greater with the new device (6.6±0.9 vs <1  mm). CONCLUSIONS The experimental results suggest that the proposed RF-assisted device provides adequate hemostatic control during transection of the renal parenchyma without additional instruments or surgical maneuvers and could therefore be a valuable adjunct for LPN without vascular clamping. The device was unsuccessful in effectively sealing the collecting system.