L. Horak, M. D., Surgical Clinic, III Medical Faculty, Charles University, Prague, CZ 

R. Svec, M. D., Institute for Pathology and Anatomy, III Medical Faculty, Prague, CZ

M. Zavoral, M. D., II Internal Dept., Central Military Hospital, Prague, CZ

J. Faltyn, M. D., Z. Zadorova, M. D., J. Hajer, M. D., I Internal Clinic, III Medical Faculty, Charles University, Prague, CZ

SUMMARY

In presented study experimental and clinical experience with laser and argon coagulation techniques are compared. Both techniques were tested using aboral parts of colon sigmoideum excised within primary operations due to carcinoma. In the experiments a Nd:YAG laser (wave-length 1064 (m) and an argon-plasma coagulator were used. Our results suggest that while argon-plasma coagulation is very effective and safe for superficial coagulation, Nd:YAG laser is suitable namely where evaporation and coagulation of a large mass of tissue is required.

INTRODUCTION

The range of indications of Nd:YAG laser, firstly used in gastroenterology sixteen years ago, has subsequently become wider (6,7). The source of working radiation is a synthetic garnet crystal enriched with elements of rare soils (Neodymium, Ytrium) which generates infrared light with basic wave length of 1064 (m. This light is transmitted by a light conducting fibre 0.6 mm in diameter. In spite of the fact that infrared light is invisible for the human eye, the apparatus contains a semiconducting laser or Helium-Neon laser which are focused into the light conducting fibre to navigate the laser. Infrared radiation penetrates about 6 mm deep into the tissues. During interaction the tissues are partly evaporated and coagulated up to the depth of 5 mm, depending on type of intervention. Longer action of the laser towards one spot leads to evaporation and deeper tissue defects occur.

Argon-plasma coagulation is a slightly newer method developed in Germany at the end of eighties. Originally it was designed for square coagulation in conventional surgery. Further development of special applicators made the extension of the method into the field of endoscopy possible. The principle of the method is a contact-heat coagulation of tissues by high frequency electric current directed by ionised argon. During interaction with electric current the tissue is coagulated, this effect is limited to only superficial part of the tissue. The depth of coagulation depends on its electric conduction resistance and heat conduction properties. The coagulated tissue releases non-conducting water vapour while the electric voltage immediately acts in the area neighbouring this non-conducting spot. The treated coagulated area is therefore larger than the one we influence. 

Due to the fact that both the above described techniques are considered to be partly competitive we have tried to shed more light on the problem using an experimental approach.

MATERIALS AND METHODS

For the experiments we used aboral parts of colon sigmoideum of five patients which were excised during primary operations due to carcinoma. In all five cases only unchanged, not irradiated intestine, macroscopically and microscopically showing no signs of cancer or other diseases, was used for the experiments. After the operation the excised intestine was stored in 0.9% NaCl solution at 5 C degrees. The experiments were performed within 90 minutes after the operation.

In the experiments with argon-plasma coagulation ionised gas is led through a Teflon probe with a ceramic ending in which a wolfram electrode (a source of coagulation voltage) is placed. The size of coagulated area can be adjusted by changes of the output as well as the probe-tissue distance under visual control (ionised argon shines blue). The method enables either tangential or axial directing of the applicator towards the treated tissue. 

The depth of coagulation depends on energy used and time of application on the spot, usually it ranges between 0.5 and 3 mm.

After exemption of the intestine from NaCl solution it was placed on a wet piece of gauze on the subjacent table of the apparatus. The probe-mucous membrane distance was 5 mm, we used output of 90 W. Time of application on one spot of the mucous membrane was 10 seconds. Ten spots were treated according to the described procedure, all of them were subsequently examined histologically. During the second phase of the experiment we tried to cause an intentional perforation of the intestinal wall. Therefore we directed a 90 W ray on one spot for 3 minutes. We have observed an enlargement of the coagulation trace on the mucous membrane however, the intestinal wall was not perforated macroscopically.

In the experiments with laser energy transfer is performed through a flexible fibre with diameter of 400 or 600 (m which easily passes through the working duct of the endoscopes. The control of application is easy due to the guidance laser. The coagulation or vaporisation of tissues is possible only in the axis of the fibre. A special fibre is needed for the tangential coagulation. The extent of the treated area can be in part regulated by adjustment of the fibre-tissue distance, the depth can be influenced by adjustment of the output (from 15 to 100 W) and time of application. In our experiment a 50W output, commonly used in clinical practise, was used. The fibre-tissue distance was 10 mm, diameter of the trace was 1 mm. We have treated 10 spots, time of each application was 10 seconds. During the second phase of the experiment we tried to cause an intentional perforation of the intestinal wall. After the experiment the dissection was fixated by formol and examined histologically.

RESULTS

After a standardised preparation and staining the dissections were examined histologically. In all 10 spots treated by the argon-plasma coagulation only coagulation lesions of the mucous membrane were identified, the depth of coagulated zone was not greater than 2.5 mm. Only on the spot where we tried to cause the intentional perforation the submocosis was coagulated, the muscular layer remained intact. While the laser treatment was used a part of the mucous membrane evaporated, the vaporisation zone reached in all spots examined 2.5 mm. The vaporisation zone was followed by a zone of coagulation to a depth of 3 mm, reaching the muscular layer, greater part of the muscular layer and serosis remained intact. A macroscopically visible perforation occurred after 70 seconds when the fibre-tissue distance was 10 mm, diameter of the trace was 1 mm and the output 50 W. In fixated dissections a perforation defect was identified histologically, a coagulation zone of 3 mm was found at margins.

DISCUSSION

The literature concerning the use of both techniques (2,4,6,7) was published by authors who use in their endoscopic practise either the first or the second method. Authors of the presented study have experience with both techniques which they use.

From their own clinical practice they prefer Nd:YAG laser when evaporation of larger volume of tumorous tissue is required, e.g. in recanalisation operations for intestinal malignant tumours. Laser can also be used in treatment of large square rectal adenomas in which wire-loop removal and coagulation with argon plasma coagulator was not successful. 

The advantage of argon plasma coagulation is better availability of the apparatus owing to price, the apparatus is possible to use even for the treatment of squarely bleeding lesions. The availability of laser is significantly lower.

In the experiments with human intestine in our experimental setting the heat conduction and impact of tissue perfusion which plays a part in clinical conditions cannot fully exert their effects. Despite this, the model used undoubtedly confirms the experimental data obtained with Nd:YAG laser in animal models. We therefore consider the experimental results of our studies with argon plasma coagulation sufficiently evidential.

Our results unambiguously proved laser as an effective tool in treatment of large tissue volumes and in reaching immediate recanalisation by evaporation of the tumorous masses. The possibility of intestinal perforation can be decreased by a long term clinical experience of the staff. 

On the contrary, safety of work with argon plasma coagulation is, according to our experimental data, much greater.

CONCLUSIONS

Argon plasma coagulator and Nd:YAG laser can be considered partly competitive techniques. In majority of endoscopic interventions argon-plasma coagulation (4) becomes prevalent. Laser remains optimal for endoscopic purposes mainly in removing voluminous masses of tissues and especially for recanalisations of stenoses of gastrointestinal tract. 

Literature available with the publisher