Ultrasonic dissectors (UDs)

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摘要

The description of ultrasonic dissectors (UDs) covers all aspects of such instruments.
The key steps of the description are presented in a step by step way: utrasound cavitation, ultrasonic dissectors, advantages of UDs, drawbacks of UDs, indications, features of scissors.

媒體類型

刊物

2002-03

普通的

最愛

音訊

數位出版

WeBSurg.com, Mar 2002;2(03).
URL: http://www.websurg.com/doi-ot02en248.htm

Ultrasonic dissectors (UDs)

1. Introduction

High Frequency electrocautery
In surgery, High Frequency (HF) electrocautery has been considered one of the best means of performing hemostasis for many years. As endoscopic surgery developed, new problems related to the use of HF currents arose. Internal burns were observed. Their origins are numerous (Refer to ‘Electrocautery and high-frequency currents in surgery’ by D Mutter on www.websurg.com).
Ultrasonic dissectors (UDs) are particularly adapted to endoscopic surgery for the following reasons:
- the risks of monopolar coagulation;
- the limitations of bipolar coagulation;
- the need to minimize the surgeon’s interchange of instruments.

Ultrasound
UDs function with ultrasound waves.
These are elastic waves with a frequency ranging from 20 kHz to several hundred mHz. Ultrasound offers the specificity of interacting with the setting in which it propagates when its wavelength is similar to the dimensions of the molecular chains forming that setting. This is the case for certain biological tissues.
Another interesting feature is that ultrasonic waves have a very short wavelength. They propagate almost without diffraction.
Waves with frequencies lower than 20 Hz are called infrasonic. They are used in diagnostic ultrasonography. Waves with frequencies higher than 20 kHz are called ultrasonic, and are described in this chapter.
There are two different ultrasonic technologies available: the ultrasonic cavitational aspirator and the ultrasonically activated scalpel.

2. Ultrasound cavitation

• General principles

The ultrasonic cavitational aspirator device is composed of a generator and a handpiece harboring a transducer that produces a vibration at a frequency of approximately 23 kHz. The energy is sent to a fine, tapered, hollow aspirating tip. The vibration of this hollow tip produces a lengthwise displacement of about 200 microns.
This movement is very rapid as the tip goes back and forth over tissues. This induces pressure changes that fragment cells and dilate spaces between these cells. Such a phenomenon is called cavitation.
The effect of cavitation originates from the creation, expansion, and then the implosion of bubbles within a fluid setting. The gas contained within these cavities is compressed. The implosion of gas bubbles occurs as energy is restored via a shockwave. This causes massive mechanical and thermal effects. In biological tissues, cavitation occurs particularly in cells that contain the most water.
These devices offer permanent irrigation of the target tissue, which improves tissue selectivity and aspiration of tissue debris.
1. Generator of the ultrasonic cavitational aspirator
2. Energy is sent to a hollow aspirating tip.
3. Effect of cavitation

• Effects on tissues

The ultrasound and cavitation device has no coagulation effect for two reasons:
1) constant irrigation by a cold solution;
2) the contact zone with the tissue is very narrow.
The ultrasound and cavitation device has selectivity for certain tissues: it destroys cells that are rich in water and adipocytes preferably. On the other hand, collagen-rich tissues such as nerves or endothelial cells are preserved. The aspiration set included in the ultrasound and cavitation device sucks in cell debris and helps identify the remaining collagen-rich structures. The main application is the skeletonization of nerves and vessels.

• Applications

- hepatic surgery: skeletonization of vessels and small bile ducts;
- laparoscopic cholecystectomy;
- others: skeletonization of vessels during laparoscopic colectomies, adrenalectomies and thoracoscopic esophagectomies.
1. Skeletonization of vessels
2. Laparoscopic cholecystectomy
3. Thoracoscopic esophagectomy

• Drawbacks

- adds to the clutter of available systems (cannot be integrated with a video unit);
- production of particles: the cavitation and irrigation effect produces several particles that impair vision (especially in laparoscopy). This also raises the problem of the potential dissemination of malignant cells.
The absence of the coagulation effect or division requires the use of another means of hemostasis. This drawback is acceptable in open surgery, yet it is an obstacle in endoscopic surgery as the surgeon is intent on limiting the use of too many instruments.
On the whole, the ultrasound and cavitation device has too many drawbacks in endoscopic surgery. Ultrasonic dissectors, which have been developed for many years, are most suited to minimally invasive surgery.

3. Ultrasonic dissectors

• General principles

• Transducer

An ultrasonic dissector is composed of a generator, an acoustic transducer located in the handpiece and an instrument. The transducer comprises a piezo-electric crystal set between two metal cylinders. It converts electricity into a mechanical vibration whose frequency is either high (>55 kHz), or low (23 kHz), depending on the model.

• Vibrations

The maximal amplitude of the vibration ranges from 80 to 200 microns, depending on the model. The mechanical vibration is sent via a metal rod to an instrument that may be a pair of scissors, a hook or a coagulating ball. It propagates to the shaft of the instrument along vibrating nodes. To obtain optimal efficacy at the level of the active blade, the rod should be long enough, ie a multiple of the amplitude. It is therefore not possible to shorten or lengthen an instrument at will.
1. Electrical energy transformed into mechanical energy
2. Propagation of the vibrating wave onto the shaft of the instrument

• Coagulation

To obtain coagulation, the tip of the instrument should be large enough. Hemostasis is poor when a bevelled blade is used as the division effect occurs before coagulation (Amaral and Chrotstek, 1997). When the surface of the blade onto which the vibration is applied is narrow, the cavitation effect prevails over coagulation. For this reason, certain companies favor a relatively low frequency (23.5 kHz) and an elevated maximal amplitude (200 micrometers), as this permits a more homogeneous distribution of the vibration over the whole length of the blade. The efficacy of UDs does not depend on frequency alone or on the maximal vibration amplitude, but rather on their combination. Coagulation resulting from the cavitation effect depends on sound velocity that originates from amplitude and frequency.
Tissues are denatured via 3 mechanisms: heat from friction, mechanical wear and damage and cavitation.
1. Ultrasonic scissors
2. Propagation of the vibration onto the blades of ultrasonic scissors

• Effects on tissues

• Heat from friction

When the temperature exceeds the boiling point of cells, these explode via air bubbles formed from the boiling water. The temperature needed for the functioning of UDs is lower than the boiling point of water. This induces the denaturation of collagen, forming a gel that is essential in the hemostasis of vessels.

• Mechanical wear and tear

Mechanical vibration, when applied for a long time, ends up causing mechanical wear and tear of the vessel and its eventual division. Friction increases with the amplitude. It is also increased by the pressure exerted on the blade by the surgeon.

• Cavitation

This effect can be easily observed by dipping the blades of ultrasonic scissors in a glass of water. The cavitation effect comes from the creation, expansion and then the implosion of bubbles in a liquid setting. The gas contained within these cavities is compressed. The implosion of gas bubbles occurs as energy is restored through a shockwave that breaks up the tissue. Experiments have shown that UDs can coagulate vessels up to 5 mm in diameter (Mueller and Frizsch, 1994).

4. Advantages of UDs

• Current

No current is transmitted. It is possible to perform coagulation in the close vicinity of sensitive structures (bile ducts, colon, etc) without the risks pertaining to the distribution of electric current (Amaral, 1995).

• Low temperatures

UDs are effective when used at a temperature of about 80°C whereas HF currents produce a temperature higher than 100°C. There is therefore less risk of thermal injuries to neighboring organs with the former. Meltzer et al. (1994) compared seromyotomies of the lower esophagus in a model. They were performed either by electrocautery or by UDs. They showed that thermal injuries were 4 times more likely with electrocautery than with UDs. Hambley et al. (1988) showed that thermal injuries were stretched over 1 mm with UDs versus 10 mm with electrocautery when skin incisions were performed in animals.

• No charring

With the low temperatures, charring of the blade does not occur. According to Amaral and Chrotstek (1997), this absence of charring might account for the lower rate of postoperative adhesions with UDs than with HF currents. The charring observed with bipolar electrocautery may account for certain coagulation-induced accidents. These occurred during the handling of bipolar graspers owing to the pressure exerted to free the jaws of the coagulum grasper.
There is a low production of smoke related to the low temperatures of the device. This ensures better visualization and might be behind the low number of postoperative adhesions. However, the cavitation phenomenon induces a slight fog of particles. Although it resolves more rapidly than the smoke induced by electrocautery, this effect may well cause some impairment. Additionally, problems related to the possible dissemination of neoplastic cells via the smoke may also affect the particles disseminated by UDs.

• Multifunction

When used with scissor-like tips, UDs are amongst the few multifunction instruments available commercially. They may be used as graspers, dissectors, coagulating graspers or scissors. Such features limit the need for instrument changes, which may represent up to 10% of the total operative time in minimally invasive surgery. Swanstrom and Pennings (1995) compared the use of ultrasonic scissors and clip appliers to perform hemostasis of short vessels during laparoscopic fundoplications. They observed that there were more active hemorrhages and subserosal hematomas with clips than with UDs. Laycock et al. (1996) showed that the time required for the division of short vessels was significantly shorter with ultrasonic scissors than with clips.

5. Drawbacks of UDs

• Limitations

Diameter: there are currently no instruments less than 5 mm in diameter.
Shape of the effector: the rudimentary shape of the tip limits the precision of the instrument in dissection, as the mechanical vibrations generated by ultrasound can only be transmitted in a straight line. However, Ethicon marketed a curved tip recently.
Pedal control: all systems use a double pedal. When added to the pedals in electrocautery, they cause crowding. This is also a source of error.
1. Blade of curved scissors
2. Pedals for ultrasonic dissector
3. Coagulation
4. Division

• Incidents and accidents

Ultrasound scissors are safe and effective instruments. However, incidents or accidents may occur. They can have 3 potential causes (A, B and C):
A. the cavitation effect: if the tip of the instrument inadvertently comes into contact with the organ (vessel, intestine, etc), a direct injury induced by cavitation may occur.
B. the production of heat: the temperature of the blades varies depending on the activation time. Below 5 seconds, the temperature averages 80°C. Beyond 10 seconds, it can reach up to 200°C. In animals, thermal injuries have been observed up to 21 mm from the blades.
C. mishandling.
1. Excessive traction on the instrument
2. Vessel incompletely charged
3. The active blade is in contact with an adjacent organ.
4. The tip is in contact with an adjacent vessel.

• Incidents and origins

Incidents and accidents are related to the misuse of instruments.
Incidents and their origins are summed up in the table opposite.

6. Indications

• Cholecystectomies

The use of UDs in endoscopic surgery is still limited as the product is recent and is expensive. Amaral conducted a consecutive series of 200 laparoscopic cholecystectomies using an ultrasound hook (UltraCision™, Ethicon-Endosurgery). For the 100 last patients in the series, it was not necessary to use electrocautery. A comparative study based on 50 laparoscopic cholecystectomies performed by electrocautery and ultrasound dissection did not show any difference in postoperative outcome, except in postoperative leukocytosis where it was significantly higher after electrocautery than after ultrasound dissection (Amaral, 1995).

• Other indications

UDs are especially interesting when there are several vessels to control, particularly when these vessels are located within thick mesenteries. Several publications reported the worth of UDs in fundoplications (Swanstrom and Pennings, 1995; Laycock et al., 1996), splenectomies (Gossot et al., 1999) or colectomies (Fowler and White, 1994). In Nissen fundoplication, Laycock et al. (1996) showed that the use of ultrasonic scissors to divide short vessels was significantly more rapid than clips and induced less bleeding. In another similar comparative study, it was reported that ultrasonic scissors induced less active bleeding and fewer hematomas than clip appliers (Swanstrom and Pennings, 1995).
1. Short vessels

7. Features/scissors

• Features

Technical features are described in the table opposite:
Technical features of the 4 ultrasonic devices currently available (the amplitude in the vibration may vary slightly with the type of instrument used)

• Scissors

To date, there are 3 brands of UDs on the market: the Ultracision™ (Ethicon-Endosurgery), the AutoSonix™ (Tyco) and the SonoSurg™ (Olympus).
The scissors by UltraCision™ (Ethicon-Endosurgery) may be used with 3 different positions (flat blade to coagulate; cutting blunt blade to coagulate thick vessels; sharp cutting blade to divide). These positions may be selected by a wheel situated on the handpiece. The SonoSurg™ (Olympus) and the AutoSonix™ (Auto-Suture) only offer the position of the blunt blade. The division is not obtained via the cutting position but rather by the brief use of the maximal power setting (100%) after the coagulation phase (60-70% of the maximal power). These 2 types of power are selected by a pedal. The SonoSurg™ has a HF connection, which may be useful in case of sudden bleeding, when hemostasis should be done rapidly. SonoSurg scissors are autoclavable and reusable. Ethycon and Tyco scissors are disposable. Hooks are reusable in all 3 brands.
1. UltraCision
2. AutoSonix
3. SonoSurg
4. Cutting blade used for division (UltraCision)
5. HF Connection (SonoSurg)
6. Autoclavable and reusable scissors (SonoSurg)
7. Straight hooks (SonoSurg); curved hooks (UltraCision)

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