The Carbon Dioxide Laser Scalpel

Review/Oorsigartikel

EJDURANTE*

reaching the lower energy level are re ABSTRACT excited, producing a continuous flow of The CO2-laser is currently used as a scalpel by a large number of medical laser energy. The atoms leaving the surgeons, but in the field of veterinary surgery, relatively little has been higher energy level must reach and leave published on the subject. A review of the origin of medical lasers. the basic the lower energy level as fast as they physics of laser energy production and the characteristics of laser light was arrive in order to accomplish their therefore considered necessary. This review includes a discussion on how the process of de-excitation. This is optical radiation generated by the different lasers is absorbed. the cutting important because quick de-excitation

power of the CO2-laser, and the effect on healing, tensile strength and contributes to the power of the laser haemostasis when used in the skin, linea alba and gastrointestinal tract. output and secondly, only the atoms at rest are available for re-excitation. Laser energy has 3 unique Key words: CO2-laser, physics, absorption. veterinary surgery, healing, tensile strength, haemostasis. characteristics: coherence, monochro macity and collimation23 . This means that laser waves travel in space in phase Durante E.J. The carbon dioxide laser Journal of the South African. scalpel. (coherence), as a beam formed by waves Veterinary Association (1991) 62 No.4, 191-194 (En.) Department of of the same length (monochromacity) Companion Animal Medicine and Surgery, Faculty of Veterinary Science, and in almost parallel configuration Medical University of Southern Africa, 0204 Medunsa, Republic of South (collimation). It is because of these Africa particular properties that the laser beam can be transported by mirrors and lenses and focused in very small spots where led optical resonator47 (Fig. l). Under the power density can be as high as 1 INTRODUCTION normal circumstances of light MW/cm216. At a distance of 30 m the Albert Einstein developed the theory of energy beam still maintains almost the stimulated emission of light which is the generation, an atom absorbs a photon, ) and as a result the electrons move to original cross-section and can be 1 basis of what is known today as the 1 higher energy orbits. Subsequently, the focussed upon a lens as small as 50 0 laser. In 1950 the precursor of the l6 2

atom emits the photon and the electrons mm • The scattering of laser energy

d modern-day lasers was assembled and

e move back to their lower energy orbits, increases with the decrease in t named MASER (Microwave Ampli a releasing in the process a.disarranged wavelength. The gas used as laser

d fication by Stimulated Emission of

( form of energy termed "incoherent medium determines the wavelength and

r Radiation). In 1960, Maiman was the

e therefore the light produced is either fIrst scientist to build a laser from a rod light". This is a spontaneous physical h s s process. On the other hand, "coherent visible or invisible (infrared). i • l of crystalline rubi The word LASER b was created as an acronym for Light light" is only generated inside a laser u tube during the process of amplification ABSORPTION OF LASER ENERGY P Amplification by Stimulated Emission of

e Laser light is absorbed by living tissues Radiation420. The two lasers used most by stimulated emission. This is usually h t triggered by an electric discharge inside and immediately converted into thermal commonly in the medical field, the y the optimal resonator (Fig. 1) that causes energy, in a manner determined by the b

carbon dioxide and neodymium-yttrium the excitation of a number of atoms of type of laser used (C0 , neodymium d aluminum-garnet (neodymium-Y AG). 2 e t 4 the laser medium. This discharge is YAG, argon, etc.) and the wavelength.

n lasers, were introduced in 1964 .

a l6 larger than the discharge that occurs The termal effect of a surgical laser is'

r Fisher defined the laser as a generator g during the spontaneous process. The essentially one of denaturation of the of a unique form of light or electromag e c netic waves, known as coherent above-mentioned phenomenon is known complex substances that form the n as "population inversion"47 because, different body tissues and .with which the e radiation, which is not found in nature. c i under normal circumstances, most atoms laser beam interacts. The absorption of l

This light can be produced by the r are at rest. The laser medium is now laser energy is influenced mainly by 2 of e excitation of a solid active medium d excited and unstable and therefore the the body's chromophores, namely water

n (solid state lasers) or as gaseous medium It u atoms begin to move to the lower energy and haemoglobin". is also influenced

(gas lasers), the latter being the type y level, each one releasing a photon in the by the scattering properties peculiar to a a most commonly used in medicine and process. When a photon, produced in particular type of laser. Consequently, w surgery. A gas laser is formed by a laser e t this manner, strikes an excited atom, the penetration may range from deep to

a tube filled with a gas or laser medium atom moves to the low energy level, superficial. Haemoglobin absorbs the G

(e.g. COrlaser). Two mirrors placed at t releasing an extra photon identical to the light of some lasers, for example argon, e both ends of the ~ube enclose the so-cal- n original one. In this way the process is rendering them ineffective as cutting i b "stimulated". The multiplication of tools unless the surgical field 'is" a

S completely free of blood. Otherwise the 'Department of Companion Animal Medicine and photons has been called "light am y Surgery, Faculty of Veterinary Science, Medical plification" and the energy thus energy is absorbed entirely by this layer, b University of Southern Africa, P.O. Box 0160, d generated in known as "laser light"2347. causing its coagulation without having e c 0204 Medunsa, Republic of South Africa This is a cycle during which the atoms reached the tissues which it is meant to u d 0038-2809 Jl S.Afr.vet.Ass. (1991) 62(4):191-194 191 o r p e R piece from the target so that it enlarges its diameter. This results in the vaporisation of a large area._ When the Pump Source focussed beam of the CO2-laser reaches the tissue, division occurs due to cell Electrical Chemical Mechanical vaporisation' 924. The high-power of the beam determines a sudden increase in the temperature of the exposed area that causes the inter-. and intracellular water Partially to boil voilently (l00°C). This process Opaque Opaque mirror mirror results in the disintegration of the cells due to the expansion of steam and the Lase Lasing Medium Laser~ Laser ejection of the cell's solid components27...... --~~.. . This cellular debris is heated further to Light -...... ;A...:..c:::..;t:..:..iv:....;e:;...... :.M... e=.d=i=u=m..:...... :..W.:..;h..;.;e::.;;n..;...... :E::.:x..:.;c::.;i.:.;:te"""d:;...... > Light Output ~ the point of combustion as it moves Optical Resonator j through the beam's path, resulting in a l, or Optical Cavity . thick plume of smoke. At the same time, part of this carboni sed material is deposited along the wound edges giving the erroneous impression that the 24 incision of the tissue is due to burning •

4 A photographic study of laser wounds Fig. I:Mechanism of laser light production (modified from Bailin et al. ) has shown that burning temperature is not reached at the impact site. During tissue evaporation, the thermostatic effect of boiling water would maintain incise. The energy generated by the very turbulent. This was probably due to the temperature at the wound edges close neodymium-Y AG laser is poorly absor shock waves produced by the sudden to 100°C24. The small size of the beam bed by water and haemoglobin, and thus, formation of steam deep down in the and the poor heat conduction of soft penetrates deeply into the tissues. The tissue. This in tum can be explained by tissues account for the destruction of a CO2-laser is almost completely absorbed the deep penetration of the beam at the very thin layer of cells when this laser is by water and as a result only penetrates impact site due to the reduced absorption used as a scalpeP6. Unlike the stainless the tissues superficially, with little of these types of laser energy by the 6 56 steel blade, the laser beam produces a scattering 26 27. Heat conduction will body tissues . For this reason pulsed conical inCISIon with a width determine the volume of tissue beyond ruby and neodymium lasers were not proportional to the power and inversely the incision line which will be affected suitable for surgical use. In 1970 a CO2- proportional to the speed of the incision by the thermal energy. The temperature laser for surgical purposes was When the laser power is high and the )

1 generated in a tissue exposed to the laser introduced and its potential medical speed of incision is slow, the 1 beam is determined by its water content. applications were discussed49. 0 conductivity of the heat away 'from the 2 Tissue water acts as a buffer, main centre of the crater also increases. This d e taining the temperature in the interaction THE CARBON DIOXIDE LASER leads to devitalisation of the wound's t a site at 100°C1627. Once the water in the The CO2-laser light is emitted in the margins which can be seen d (

tisue has evaporated, the buffer effect infrared region at a wavelength of 10,6 macroscopically as a blanching of the r e will disappear and the temperature will nm. It is well absored by all the body area around the crater, and is h s increase substantially. If irradiation is tissues, with the exception of bone. This

i microscopically demonstrated by the l 36 b prolonged, carbonisation may occur . tissue has a very low water content presence of coagulation necrosis and u The temperature at an impact site in which causes the laser energy to nuclear-cytoplasmic modifications in the P 37 e tiSsues with very low water content, such generate very high temperatures, leading cells close to the impact site . For this h t as bone, can reach 1 OOO°C. to carbonisation and thermal necrosis. In reason, the CO2-laser scalpel should be y contrast with the lasers emitted in the used at the maximum possible power b

d ORIGIN AND DEVELOPMENT OF visible region of the light spectrum, the that the surgeon can manage, and for the e t MEDICAL LASERS absorption coefficient of CO2-laser light shortest possible time. This will ensure n l a After the creation of the ruby laser, me is not affected by the colour of the tissue that minimum secondary damage occurs r g dical researchers spent a great deal of it penetriltes' 55. 17. When an unfocussed beam is used, the

e time investigating the potential The ability of this laser to incise or c spot of light is considerably larger. This n applications of lasers in the medical vaporise a tissue is determined by the

e allows for the vaporisation of large c i field. The nrst experiments were done instantaneous transformation into heat of volumes of tissues or the coagulation of l

r with the ruby laser and later the the absorbed light within a depth of blood vessels larger than 0,5 mm or the e 22 d neodymium laser in areas such as about 0,2 mm . The effect of this occurrence of both of these phenomena n 550

u oncology, dermatology and ophthalmo thermal interaction is determined by the at the same time .

y log~o. The energy produced by these energy:density26. The depth of the a lasers was delivered in the form of short incision, therefore depends primarily on WOUND HEALING, TENSILE w e t pulses. Therefore the excision of even both the 'power used and on the speed at STRENGTH AND HAEMOSTASIS a small tumours was extremely which the beam is swept across the atea. IN TISSUES INCISED WITH THE G

t impractical, since only a minute amount The light of a CO2-laser can be delivered CO2-LASER e

n of tissue could be destroyed with every to the surface of a tissue in 2 ways. Until 1970, all research related to the i b pulse. The high-energy pulsed ruby and Firstly, the beam may be focussed on a healing process of surgical wounds was a

S neodymium lasers that appeared later very small spot causing the division of based on incisions made with steel

y were more effective, but it was soon the tissues. Secondly, the beam may be scalpel blades. With the advent of the b

d discovered that their effect on tisues was unfocuss~'d by withdrawing the hand- CO2-laser, surgeons needed more e c 192 OQ38-22809 Tydskr.S.Afr.vet. Ver. (1991) 62(4):191-194 u d o r p e R