Short CommunicationKurume Medical Journal, 48, 251-253, 2001

The B-Wave Bipolar Snare for Endoscopic Treatment

YASUMI ARAKI, NOBUYA ISHIBASHI, YUKIYA KISHIMOTO, MOTONORI NAKAGAWA,

KEIKO MATONO, TERUO SASATOMI, YUTAKA OGATA AND KAZUO SHIROUZU

Department of Surgery, Kurume University School of Medicine,

Kurume 830-0011, Japan

Key words bipolar snare, endoscopic resection

Bipolar electrosurgical instruments are commonly used in luminal endoscopic surgery. Compared to monopolar electrosurgery, it provides increased safe-ty, because it precisely confines the energy delivery between the tines of the instruments [1-5]. In 1979 Williams described preliminary clinical experience with a bipolar polypectomy system that used a dou-ble channel colonoscopy to introduce an insulated

grasping forceps as the return electrode in addition to the snare loop electrode [3]. Treat in 1983 described their experimental results with a bipolar snare design that employed a snare electrically separated into two halves by an insulating bead located at the distal end of the snare [6]. The standard bipolar snare and new instrument will be discussed, with the advantages and drawbacks.

With importance placed on the safety of the

endoscopic resection, a new concept of bipolar snare

was developed by the Department of Surgery at

Kurume University Hospital in cooperation with

Zeon Medical Co. Figures 1 and 2 illustrate the

difference between the standard bipolar snare and the

new B-wave bipolar snare systems. The standard

bipolar snare system is electrically separated into two

tubings, with the distal end of snare insulated with a

ceramic tip. The new B-wave bipolar snare, in which

the wire serves as one electrode and the other

electrode is set at the end of the sheath directly con-

tacting the tissue, is designed to produce a difference

in current density between the sites in contact with

the two electrodes, thereby enabling cauterizing

resection. Since the surface of the wire electrode is

coated with fluorocarbon resin insulator, the elec-

Fig. 1. Standard bipolar snare system. The stan-

dard bipolar snare system is electrically separated

into two tubings, with the distal end of snare insu-

lated with a ceramic tip.

Fig. 2. New B-wave bipolar snare system. The

new B-wave bipolar snare, in which the wire

serves as one electrode and the other electrode is

set at the end of the sheath directly contacting the

tissue, is designed to produce a difference in

current density between the sites in contact with

the two electrodes, thereby enabling cauterizing

resection.

Received for publication April 5, 2001Address correspondence to: Yasumi Araki, M.D., Department of Surgery, Kurume University School of Medicine, 67 Asahi-machi, Kurume830-0011, Japan. Tel: 0942-35-3311 Fax: 0942-34-0709 E-mail: ksurgery@kurume.ktarn.or.jp

252 ARAKI ET AL.

trifled area in the tissue that the wire electrode

contacts is small, resulting in a high current power

and an increased heat generation. On the other hand,

the sheath electrode gives a larger electrified area

and thus a lower current density in the contacted

tissue than the wire electrode. In an in vivo experi-

mental system consisting of pseudopolyps made

from pigs' mucosa of the colon, the safety advan-

tages of bipolar and monopolar systems were demon-

strated.

The authors have performed selective polypec-

tomies for approximately one year using the B-wave

bipolar polypectomy system without serious compli-

cation such as bleeding and perforation. The snare is

routable during endoscopic polypectomy, which

enabled us to easily catch polyp. Furthermore, due to

the absence of a ceramic bead at the end of the snare

that the standard bipolar system has, the B-wave

bipolar snare system did not cause incomplete resec-

tion or any slight bleeding at final resection.

The B-wave bipolar snare has a new structure employing the advantages of the standard bipolar snare and removing its drawbacks. With the wire loop serving as the first and second electrodes, the standard bipolar snare is characterized by less elec-trical branching because the energy delivered is pre-cisely confined to the tissue subject to cauterizing resection, and by less electrification toward the intestinal wail due to the electrifying direction con-sistent with the resecting direction; it provides the advantages of decreasing the risk of perforation, decreasing the effects of body fluid, and decreasing the adverse influence on metal devices such as a

pacemaker that are problems with the monopolar snare [7] and making it easier pathologically to diag-nose the resected tissues. On the other hand, there are the following drawbacks:

1) The ceramic tip insulating the two electrodes acts as a resistor during polypectomy, which causes incomplete resection and often leads to slight bleeding.

2) To generate heat in the entire tissue contacting the wire electrode, it is necessary that the two elec-trodes should be equal in the area of tissue that they contact. However, the adhesion of tissue due to burn-ing causes a difference in contact area (difference in current density) between the electrodes, resulting in one-sided cauterization.

3) There is the risk that the ceramic tip at the end

of the snare may be damaged by heat. In order to remove these drawbacks of the standard bipolar sys-tem, the B-wave bipolar snare, in which the wire

serves as one electrode and the other electrode is set

at the end of the sheath directly contacting the tissue,

is designed to produce a difference in current density

between the sites in contact with the two electrodes,

thereby enabling cauterizing resection.

With Joule's law [W (watt)=I (current density)2

•~R (resistance)•~t (time)] applied, the principle of

cauterization by the B-wave bipolar snare is that an

electric current is passed through the tissue between

the first electrode set at the end of the sheath and the

second electrode at the wire, which causes heat

generation in the resistor (tissue). Since the surface

of the wire electrode is coated with an insulator (flu-

orocarbon resin), the electrified area in the tissue that

wire electrode contacts is small, resulting in a high

current density and an increased heat generation. On

the other hand, the sheath electrode gives a larger

electrified area and thus a lower current density in

the contacted tissue than the wire electrode. The

increase in tissue temperature is proportional to the

square of current density, so that heat is generated at

the site in contact with the wire electrode, but heat

generation is lower at the site in contact with the

sheath electrode, which makes it possible to cauterize

only the tissue that the wire electrode contacts.

In the new B-wave bipolar snare, a stranded wire

is used instead of a single wire, because, compared

with the latter, the former is characterized by:

•œ Larger surface area;

•œ Higher springiness, allowing the rhombic or hexag-

onal shape of the snare to be kept;

•œ Easiness to control uniform thickness of fluoro-

carbon resin coating; and

•œ Less extent to which fluorocarbon resin coat peels

off during cauterization.

To allow the snare, which is used endoscopically, to

grasp the polyp firmly, the size of the sheath and wire loop is limited, so that usually the area of the electrode set at the wire loop is larger than that at the

sheath, which would cause preferential heat genera-

tion at the site in contact with the sheath. In the B-

wave bipolar snare, therefore the surface of the wire having a special structure is coated with a heat-

resisting insulator to reverse the area ratio, which

makes it possible to preferentially and uniformly

generate heat in the tissue in contact with the wire loop, and thus enables the wire electrode to act as a

monopolar. As a result, besides the merits of stan-

dard bipolar snare system, the B-wave bipolar snare

can make uniform cauterization hardly causing incomplete resection, gives a clear surgical margin

making histopathological examination easy, and pro-

Kurume Medical Journal Vol. 48, No. 3, 2001

B-WAVE BIPOLAR SNARE 253

vides an economical advantage because its structure

is so simple that the snare is easy to wash and dis-

infect, and thus reusable.

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maker. Endoscopy 1994; 26:270.

Kurume Medical Journal Vol. 48, No. 3, 2001