Partial nephrectomy using radiofrequency incremental bipolar generator with multi electrode probe: experimental study in bench pig kidneys

The diffusion of screening programs and the use of modern techniques of imaging [1] have led to an earlier diagnosis of renal neoplasms [2, 3].

Radical nephrectomy was always considered the therapeutic gold standard of renal tumours up to the early 90’s, when both the minimal invasive and partial renal resection approaches, as Nephron Sparing Surgery (NSS), had became established.

Nephron Sparing Surgery in localized renal tumours demonstrated an oncological outcome comparable with radical nephrectomy [4], with better long-term preservation of the renal function and increased overall survival [5, 6].

NSS is the gold standard in tumours of ≤ 4 centimetres (pT1a) [7]; and in selected cases in the T1b (4 – 7 cm) forms [8].

The experimentation has been carried out in two phases. During the first, the dedicated generator and the four-needle inline probe were developed and set up. In the second phases the device was tested on 27 bench kidneys for a total of 47 polar resections.

Phase 2

27 experimental tests were carried out on pig kidneys for a total of 47 polar resections.

The four-needle probe was inserted at the renal pole and coagulation was started.

Cessation of energy supply by the generator took place automatically and adequate parenchymal coagulation was obtained (Figure 1).

At the end of the coagulation procedure, the time from the start to the automatic stop of the generator was obtained for each insertion.

The maneuver was repeated along the line, inserting the probe until completion of the first line.

Successively, a second, distal, line of insertion of the probe was carried out at about 5 mm from the first (Figure 2).

At the end of the second line, a caliper was used to measure the slice of coagulated tissue.

Four-needle conical-pointed probes were used.

The needles used were of 1.5 mm and 1 mm caliber; the power levels tested were levels 1, 3, 5, 6, 7 and 9.

With the 1 mm needle, we tested power level 5 in 6 polar resections, level 7 in 4 resections and level 9 in 5 polar resections.

With the 1.5 mm needle, tests were power level 1 in 2 cases, level 3 in 2 resections, level 5 in 9 resections, level 6 in 2, level 7 in 4, and level 9 in 13 polar resections.

Following coagulation, the parenchyma was sectioned with a scalpel along the distal line of insertion.

In 10 polar resections, we verified the possibility of applying stitches (Monocryl 2/0) on the coagulated renal parenchyma and on the exposed caliceal system following resection.

The parameters evaluated were: needle caliber, coagulation times, power level, thickness of the “slice” of coagulated tissue, eventual charring, ease of handling during the insertion and removal phases of the probe, feasibility of the application of stitches on the parenchyma and the caliceal system, and generator automatisms.

Renal tumour surgery has evolved notably since the classical description of radical nephrectomy by Robson in 1963. As well as the laparoscopic approach, the most significant change has been the establishment of nephron sparing surgery as the gold standard for T1a renal neoplasms [13].

NSS brings results analogous to radical nephrectomy from the oncological point of view, with an increase in overall survival with respect to the morbidity and mortality correlated to the complete removal of the kidney [14].

The principal difficulty in NSS is the control of bleeding, which can be obtained with clamping of the renal vessels, through compression of the parenchyma, or with the use of several devices [15, 16].

Various surgical instruments for tissue coagulation, haemostasis and parenchyma dissection are available along with sealants and haemostatic agents.

Instruments include the Water Jet Dissector, the Argon Beam Coagulator, the Tissuelink Floating Ball, the Harmonic Scalpel, Microwave Tissue Coagulation, Laser and Bipolar Coagulation.

Radiofrequency coagulation, born in the 90’s for ablation of liver neoplasms, and has been successively used to facilitate hepatic resection. The technique consisted of coagulating the liver parenchyma around the neoplastic nodule with a monopole “cooled-tip” needle to allow transection by scalpel. Later described in major liver resections [10], the technique is commonly known as “Radio-frequency assisted liver resection” (RFA-LR) [17].

In this connection, we planned and realized a generator and a dedicated multi-needle inline probe [11, 12].

The “comb” arrangement of the electrode-needles permits the realization of “slices” of coagulation of the parenchyma around the neoplastic nodules, or along anatomic planes with closure of the blood and biliary vessels, without the Pringle manoeuvre and with little or no blood loss. The coagulated tissue can be transected by means of a scalpel.

That principle can be applied in theory to all parenchymas.

In literature there are data from several research groups on renal partial resection in animal models.

We mention Ong [18], who uses a bipolar electro-cauterizing device consisting of 2 electrode needles connected to a standard generator. Each polar resection needed about 20 “passes” of the instrument along with considerable time.

The author also mentioned the need for an impedance monitoring system to determine the completion of coagulation of the renal parenchyma.

In 2005, Mahvi [19] used a probe consisting of “plate” electrodes of 1 x 5 mm placed 1.5 cm from each other, with the energy applied between each pair of electrodes in bipolar mode, one pair at a time, with an interval of 600 milliseconds. A specific algorithm based on the impedance reached between each pair of electrodes was used to control the power delivered.

Morris [20] realized a probe with 6 inline needles connected to a RITA 1500 generator (RITA Medical System, Mountain View, CA, USA) able to produce energy at 460 Hz, with maximum power of 150 W; the power level was selected by the operator according to the thickness of the parenchyma to be coagulated.

Habib [21] has developed a 4-needle probe with a rhomboidal arrangement, called Habib 4X.

This probe has been used in the clinical setting for liver resections, partial renal resections, and for distal pancreasectomies.

According to the authors [21], NSS through that instrument is feasible and with a safety factor comparable with standard techniques without compromising the oncological outcome; however, the cost of the probe is relatively high.

RFA is therefore evidently valid also in the field of the renal parenchyma.

However, emerging from the literature is the necessity of a dedicated generator with a specific work algorithm and of a multi-electrode probe to reduce operating times.

Our system uses a multi-electrode fixed-needle probe, without the need to position manually each electrode, from which the energy is distributed automatically in each parenchymal section independently of its impedance.

This method allows for greater use of the system also for future applications such as laparoscopic probes.

The algorithm for the automatic shutoff of the electrodes allows the operator to follow and terminate automatically the treatment in each needle-to-needle zone, avoiding charring and, at the same time, guaranteeing coagulation of the tissue.

This first part of the project has been directed at the realization of the dedicated generator and the identification of the fundamental functional parameters for the renal parenchyma. The results are useful preparation for the execution of experimentation on the in vivo animal model and the realization of a laparoscopic probe.

Our experimentation on a bench model has shown that the apparatus, consisting of an automatic and original power unit, and of a 4-electrode inline probe is able to carry out effective and homogeneas coagulation of the resection “slice”.

The coagulated tissue allows application of stitches on the parenchyma and the calyceal system.

Coagulation times are short; the generator delivers energy automatically thanks to the automatic impedance checking with switching off when optimal coagulation is reached.

The best caliber for the needle-electrodes turned out to be 1.5 mm as offering sufficient rigidity to maintain trajectory and parallel condition between them.

The appropriate power level is 5.

Lower power causing longer times and thicker “slices” of necrosis, while higher levels bring shorter coagulation times, but with the risk of causing charring, non-homogeneous coagulation and difficulty in removal of the probe.

The comb configuration of the probe allows adequate coagulation in a limited time. The coagulated tissue lends itself to division by means of scalpel.

The probe is easily used both during insertion and removal.