A CARBON DIOXIDE SURGICAL LASER

Transcription

1 A CARBON DIOXIDE SURGICAL LASER R. R. HALL F.RKC.S. Department of Surgical Sciences, Royal College of Surgeons of England D. W. HILL M.Sc., Ph.D., F.Inst.lP., F.I.E.E. Research Department of Anaesthetics, Royal College of Surgeons of England A. D. BEACH A.lnst.P. Applied iphysics Division, Atomic Weaiplons Research Estalblishment, Alderm,aston CARBON DIOXIDE LASERS are of surgical importance because the light they produce is capable of destroying tissue. The output from this particular laser takes the form of an invisible, almost parallel beam of light that is in the infra-red region of the electromagnetic spectrum at a wavelength of 10.6 micro-metres (pm.). The beam is not significantly attenuated by the atmosphere, can be reflected by mirrors and refracted by lenses. If focussed to a small spot the energy is concentrated to yield an effective power of several thousands of watts per square centimetre. At the 10.6 gm. wavelength tissues act as black bodies and all incident radiation is absorbed as heat by the first 100 gm. of tissue. Litwinl et al. calculated that 1,000 watts of carbon dioxide laser power, in one second, would burn a hole in soft tissue 1 cm. square and 1 cm. deep. The light from some other lasers such as ruby and argon is able to penetrate soft tissue and cause damage in depth without disturbing the surface. Tissues vary in their response to these lasers according to the pigmentation of the tissue or its vascularity. Furthermore the output of many lasers is pulsatile, the energy being released in short intermittent bursts of a few nanoseconds (10-9 seconds) with a recovery period of several seconds in between. The peak energy of each pulse is very high compared with the mean power and causes far more damage than a continuous wave laser of comparable power. These factors form the basis of the successful use of the argon and ruby lasers in ophthalmology and their experimental application in dermatology, but renders them unsuitable for general surgery. The carbon dioxide laser has none of these disadvantages. The energy output is continuous; it acts upon tissue only in the immediate vicinity of the laser beam, and all tissues are uniformly affected. The first carbon dioxide laser was made as recently as By 1968 of vascular (Ann. Roy. Coll. Surg. Engl. 1971, vol. 48) 181 several published reports had described 'bloodless surgery '

2 R. R. HALL, D. W. HILL AND A. D. BEACH organs in experimental animals using this laser, concluding that it could provide a new surgical tool for the rapid incision of tissue accompanied by a remarkable degree of haemostasis. In 1969 the Department of Health and Social Security, in conjunction with the Research Department of Anaesthetics of the Royal College of Surgeons of England, agreed to support the development of a carbon dioxide laser and surgical ' manipulator ' by the Applied Physics Division, Atomic Weapons Research Establishment, Aldermaston. The timely innovation of the Department of Surgical Sciences at the College, together with a Freemasons' Research Fellowship, provided laboratory facilities and a two-year investigation has been made of the surgical potential of the laser. This report describes the main findings of the investigation, summarizes the observations of other workers in the field and seeks to outline the surgical conditions for which the laser is likely to be of greatest use. Laser The laser comprises a glass tube 12 mm. in diameter and 1.5 metres long containing an electrode at each end, sealed at one end by a concave gold-surfaced mirror (focal length 260 cm.) and at the other by a flat germanium output window. The tube is surrounded by a cooling water jacket. It is evacuated, filled with a mixture of carbon dioxide, nitrogen and helium at low pressure (approximately 15 mm. Hg) and a D.C. electric discharge struck in the gaseous medium between the electrodes. The tube running current is 30 to 40 ma. at 14 kv. Electrons from the discharge collide with the gas molecules and stimulate the emission of energy by the molecules, which in the case of carbon dioxide has a wavelength of 10.6 jgm. Collision of emitted photons with other molecules together with the alignment of the gold mirror and germanium window selectively amplify the radiation along the long axis of the tube so that it emerges from the window as a beam of infra-red light. Hence the term Light Amplification by the Stimulated Emission of Radiation. Manipulator The beam is directed and focussed by the surgical manipulator2 shown in Figure 1. This contains a series of gold-plated mirrors mounted on pivoting joints which together with a distal focussing lens convert the the horizontal laser beam 10 mm. in diameter into a freely manoeuvrable beam focussed to a spot 0.5 mm. in diameter. The passage of the beam along the manipulator is controlled by a foot switch and a finger switch arranged in series for greater safety. Accidental exposure to the beam can cause corneal burns so all personnel wear spectacles or shielded plastic goggles. The power output of the laser used in this study was a continuous 60 watts which was reduced to 30 watts by losses in the 182

3 A CARBON DIOXIDE SURGICAL LASER manipulator. Compared with conventional light sources this seems very weak, but when focussed as above it has a power density equal to 4,000 watts per square centimetre. This is sufficient to make a fire-brick white hot or to burn a hole in asbestos or wood almost instantaneously. When moved across animal tissues it 'burns' an incision less than one millimetre wide and several millimetres deep. If held stationary a small hole is produced which will penetrate the full thickness of the tissue. Alternatively the beam can be moved over an area of tissue which will be vaporized progressively, leaving a crater whose depth is controlled easily by the surgeon. The speed of incision or the rate of vaporization depends upon the size of the focussed beam and the laser power. If the laser is used away from the focus the power will be applied over a greater area and the rate of tissue destruction will be reduced proportionally. Fig. 1. Surgical manipulator used to direct and focus the laser beam. The end of the laser is visible on the right of the picture. When considering the surgical uses of such energy several basic questions must be answered: 1. What is the exact nature of the process of tissue destruction by this laser? 2. What is the extent and nature of tissue damage in the vicinity of laser action? 3. Will tissues heal satisfactorily following laser incision? 4. How effective is the laser as a haemostatic agent compared with surgical diathermy? 183

4 Laser action R. R. HALL, D. W. HILL AND A. D. BEACH on tissue Laser destruction of tissue has been variously described as 'burning', vaporization' and ' ablation'. Exposure to the unfocussed beam results in a lesion which develops the signs characteristic of a burn: erythema, oedema, blistering and charring. The focussed beam produces a hole and a cloud of steam and smoke. Reliable measurement of the temperature at the site of the laser impact using conventional methods is not feasible, so we have examined laser incisions in animal tissues by'means of very high speed close-up colour cin6 photography3. The experiment showed that tissue is incised by the boiling of intraand extra-cellular water to form steam which expands explosively and A.8.V_W Fig. 2. Laser incision of rat skin made with only 11 watts at 1 cm. per second (H. and E. x 50). The extent of thermal necrosis is similar to that in Figure 3. disrupts tissue architecture carrying cellular debris out of the wound. Some of the debris is charred as it passes through the beam; some of it ignites and burns, glowing white hot. The actual area of laser impact does not show any sign of tissue combustion and it is concluded that the carbon dioxide laser destroys tissue by vaporization of cellular water and that the temperature of laser impact is only 1000 C. More recent measurement of the velocity at which steam expands from the point of laser action indicates that the pressure exerted on adjacent tissue by cell disruption is small and unlikely to cause damage by shock waves or dissemination of harmful material around the wound. Several investigators have commented on the surprisingly small amount of damage seen around carbon dioxide lesions. Histological examination of numerous sections taken through laser wounds on various organs 184

5 A CARBON DIOXIDE SURGICAL LASER has shown that cellular damage occurs up to 500 gm. from the laser impact and that the depth of thermal necrosis is usually less than 100 Am. Similar wounds with the cutting diathermy produce a comparable amount of damage: the similarity is illustrated by Figures 2 and 3. Such limited necrosis was hard to explain when laser impact temperatures were thought to be very high. Having demonstrated that the incision temperature is only 1000 C., the limitation of tissue trauma is more readily understood. Rather crude attempts have been made4 to measure the rise in temperature around laser wounds, but here again conventional methods employing thermocouples or pyrometers are unsuitable. By means of Encapsulated Liquid Crystal (a substance that changes colour at certain temperatures)... ;..._1 Fig. 3. Diathermy incision of rat skin made with Matbun model DLP 12 at dial setting 8 (H. and E. x 50). we have been able to record these thermal gradients. Results show a 500 C. isotherm 400 to 500 gm. from the incision and a temperature rise of 700 C. at approximately 100 jim. These temperatures confirm the circumscribed nature of laser-tissue interaction compared with the effects of some other lasers. Wound healing The amount of necrosis at the margins of laser wounds, although small, is greater than that caused by scalpel incision. Initial reports on the healing of laser incisions were conflicting, but it seemed likely that even a small amount of thermal necrosis might interfere with healing. To investigate this possibility laser wounds in rats have been compared with similar 185

6 R. R. HALL, D. W. HILL AND A. D. BEACH diathermy and scalpel incisions, using the tensile strength of the wounds as a measure of healing. It was found5 that laser and diathermy wounds of the skin healed more slowly than scalpel wounds and it was considered unwise to recommend the laser for routine incision of the skin. However, healing of the abdominal muscle, fascia and peritoneum was not delayed and there appears to be no contra-indication to its use on tissues other than skin. Haemostasis The main feature of carbon dioxide laser action that has received most emphasis to date is its haemostatic capability. Mullins et al.6 reported bloodless, fast laser incision of the liver in Rhesus monkeys and suggested its use for the treatment of multifocal metastases in liver. Gonzales et al.7 found the laser superior to coagulating diathermy in controlling haemorrhage from the raw surface of the liver. Goodale et al.8 were able to achieve haemostasis of superficial gastric erosions in dogs more effectively with the laser than diathermy and have used the method successfully on one patient. Stellar9 has used the laser for the immediate excision of extensive full thickness burns in pigs followed by skin grafting. The laser minimized bleeding during excision better than diathermy or scalpel and allowed successful grafting with no infection or rejection. All these reports have been based on a qualitative assessment of haemorrhage. We have made a quantitative study of blood loss from the liver following laser, scalpel and diathermy incision1. It was found that measured blood loss following sub-lobar resection of liver in normal or heparinized dogs was reduced 40% by diathermy and 85 % by laser, compared with scalpel control, provided that the hepatic circulation was arrested for the brief duration of the incision. If this precaution was not observed, neither laser nor diathermy reduced haemorrhage significantly. With normal flow in the vessels, veins and arteries up to 0.5 mm. in diameter are sealed by the laser. If the flow is stopped while the vessel is divided those up to 2.0 mm. are sealed, compared with 0.5 to 1.0 mm. in the case of cutting diathermy. Thus we have been able to confirm the superiority of the laser in providing primary haemostasis. Vaporization of tissue The other, more important, aspect of carbon dioxide laser action is the vaporization of large areas of tissue in situ. Stellarll has used the laser successfully to treat experimental tumours in mice by this means. The whole tumour mass is vaporized without other dissection, leaving a dry tumour-free crater over which the skin can be closed without complication. At the present time we have not been able to conduct a controlled experiment on animal tumours. But it is clear from work on normal organs that a large mass of tissue can be vaporized in just a few minutes 186

7 A CARBON DIOXIDE SURGICAL LASER causing minimal haemorrhage, sterilizing the remaining surface and without the risk of local dissemination. The organ must be exposed as for conventional excision but can then be 'removed' without extensive dissection. It is anticipated that this will prove advantageous in tumour surgery as it provides a method of local or radical removal that minimizes the dissemination of malignant cells locally or via lymphatics and veins caused by handling the tumour during normal excision. Blood loss both during and following operation from large raw areas should be reduced and the operating time should be shorter. Whether these factors would improve long-term survival is at present unknown. Fig. 4. Surgical laser and manipulator. A new mobile unit with vertically mounted laser, suitable for use in operating theatre. Use of the laser is by no means precluded by infection: indeed it appears to be an asset under such circumstances. It is capable of vaporizing infected, necrotic tissue and the oedematous or fibrous walls of chronic abscesses and it is suggested that it should prove possible to treat such lesions by vaporization and primary suture instead of incision and drainage. It is similarly possible to incise or vaporize bone, but power levels in excess of 200 watts are necessary12. If asked what unique facility the carbon dioxide laser has to offer the surgeon, the answer must be that it can remove by vaporization organs, or parts of organs, rapidly, safely with improved haemostasis and less local disturbance than the current techniques. It can also incise tissues in a manner similar to, but faster than, cutting diathermy and with superior haemostasis. 187

8 R. R. HALL, D. W. HILL AND A. D. BEACH All our work to date has been done with a prototype laser and manipulator that could not be moved from the laboratory bench. A second instrument (shown in Fig. 4) has now been constructed for use in the operating theatre. It remains to be seen how the experimental observations outlined above can be developed to the advantage of patient and surgeon alike in clinical surgery. ACKNOWLEDGEMENTS We wish to acknowledge our gratitude to the several members of the College staff who have contributed to this project, in particular, Mr. P. C. A. Morrison and Mr. T. Cunningham for their help with power measurement and Mr. J. Manders and Miss M. Jacques who have provided technical assistance. The Pathology Department has prepared all histological material; the Anatomy Department has provided Electron Microscope facilities; Ethicon Sutures Limited at the Buckston Browne Farm co-operated in the wound healing study. We are grateful to Professor J. P. Payne for his encouragement in this work, and to Lord Brock who has given continuing support and guidance. REFERENCES 1. LrrwsN, M. S., FINE, S., KLEIN, E., and FINE, B. S. (1969) Arch. Surg. 98, BEACH, A. D. (1969) J. Sci. Inst. 2, Series 2, HALL, R. R., BEACH, A. D., BAKER, E., and MORRISON, P. C. A. (1971) Nature. In press. 4. ROCKWELL, R. J., FIDLER, J. P., EPSTEJN, R. A., NAPRSTEK, Z., FRANKE, E. K., HASHIMOTO, K., and DREFFER, R. L. (1969) 'Thermal aspects of Laser Surgery'. London Conference on Lasers in Medicine and Biology. July, HALL, R. R. (1971) Brit. J. Surg. In press. 6. MuLLINs, F., JENNINGS, B., and MCCLUSKY, L. (1968) Amer. Surgeon, 34, GONZALEZ, R., EDLICH, R. F., BREDEMEIER, H. C., POLANYI, T. G., GOODALE, R. L., and WANGEN- STEEN, 0. H. (1970) Surg. Gynec. Obstet. 121, GOODALE, R. L., OKADA, A., GONZALES, R., BORNER, J. W., EDLICH, R. F., and WANGENSTEEN, 0. H. (1970) Arch. Surg. 101, STELLAR, S. Personal communication. 10. HALL, R. R. (1971) Brit. J. Surg. In press. 11. STELLAR, S. (1970) Med. biol. Engng. 8, ROCKWELL, R. J., and GOLDMAN, L. Personal communication. DONATIONS DURING THE PAST few weeks the following generous donations have been received: 16,000 David Robinson, Esq. (further gift). 1,500 Part payment of legacy from the late Mrs. E. V. Parkes. 500 Legacy from the late Mr. E. G. Stanley. 100 Legacy from the late Mrs. E. B. M. Hobbs. In addition there have been a number of gifts under 100 which total 99 15s. The following Fellow in the Faculty of Anaesthetists has generously given a donation to the College: G. S. Ambardeker, F.F.A.R.C.S. 188