- Email: [email protected]
Diode laser and endoscopic laser surgery
Vet Clin Small Anim 32 (2002) 639–648
Diode laser and endoscopic laser surgery Kenneth E. Sullins, DVM, MS Marion duPont Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, PO Box 1938, Leesburg, VA 20177, USA
Laser equipment Diode lasers are replacing neodymium:yttrium aluminum garnet (Nd:YAG) lasers in veterinary surgery, because they are smaller, more efficient, and more cost-effective because of the semiconductor technology that produces the laser (AOC LaserCare 50, 50-W, solid-state, 980-nm diode surgical laser, Lumenis, Santa Clara, CA; Fig. 1) [1]. Although their applications are similar, commonly used medical diode lasers operate at wavelengths of 810 or 980 nm versus the 1064 nm of Nd:YAG lasers. Because these wavelengths are not in the visible spectrum, aiming beams are used to show the operator where the laser energy will impact target tissue. Diode lasers are commonly marketed in 25- to 60-W configurations. Diode laser–tissue interaction The wavelengths of the diode and Nd:YAG lasers penetrate comparative depths into tissue because they are most absorbed by melanin, hemoglobin, and darker pigments that do not usually occur on the surface. The concentration of these or other darker pigments determines the penetration at a given energy level. Nonpigmented tissue, such as cornea, absorbs none of the energy, whereas a pigmented melanoma absorbs a great deal of the energy. A caveat to this comes with the 980-nm diode laser, which has increased water absorption compared with the 810-nm diode and the 1064-nm Nd:YAG laser, and produces an efficient surface effect (Fig. 2) [2]. Subsurface, nonpigmented tissue, such as myelin, which may ordinarily have been minimally affected by these wavelengths, could be at higher risk with the 980-nm diode laser. Tissue necrosis, hemorrhage, or neuropathy are potential complications. Depth of penetration of the laser energy is a particular concern during endoscopic procedures of hollow organs.
E-mail address: [email protected] (K.E. Sullins). 0195-5616/02/$ - see front matter Ó 2002, Elsevier Science (USA). All rights reserved. PII: S 0 1 9 5 - 5 6 1 6 ( 0 2 ) 0 0 0 1 3 - X
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K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
Fig. 1. Tabletop 50-W diode laser (980 nm). The unit operates from a standard electric outlet and requires no external cooling source.
Laser delivery Quartz fiber delivery allows function in the noncontact (delivery device does not contact tissue) or contact mode. The tissue effect is determined by the wavelength and power density in the noncontact mode. The noncontact mode is described by the pure definition of light interaction with tissue. The purpose of the contact mode is to modify the raw interaction to achieve a particular effect. Laser fibers usually arrive in sterile packaging or can be sterilized using gaseous or cold sterilization techniques.
Fig. 2. Tissue absorption of common laser wavelengths. Note the relatively good absorption of the diode and Nd:YAG wavelengths in hemoglobin and melanin. The 980-nm diode laser has increased water absorption compared with the 810-nm diode and Nd:YAG lasers. (Modified from illustration provided by Lumenis, Santa Clara, CA.)
K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
641
Fiber types Noncontact or free-beam fibers are squared, cleaved, or polished, so that the coherent light is transmitted directly to the tissue (Fig. 3A). Depending on the power density, these fibers coagulate, vaporize, or ablate tissue. Power density is determined by the fiber size and the energy delivered. Noncontact fibers are used for procedures, such as ablating masses, when underlying tissue is of minimal concern. Tissue may also be coagulated in anticipation of a later slough or to minimize hemorrhage for a subsequent incisive procedure. To preserve optimal function, misshapen or crystallized tips must be stripped of the plastic outer coating and cleaved. The quality of the tip can be judged by the shape and clarity of the aiming beam. Contact fibers are sculpted or shaped to focus (or diffuse) the energy in the desired manner (Fig. 3B). Hybrid shapes, such as a hemispheric fiber, can accomplish some of both the contact and noncontact functions. The most obvious contact function is incision of tissue where the desired effect is at the tissue surface. Depth of the tissue effect is controlled in the contact mode by the shape of the fiber tip. Although the conical tip is the most commonly used contact
Fig. 3. Laser fibers are shaped to produce the desired effect. (A) This noncontact fiber has been cleaved to deliver a coherent laser beam into tissue directly ahead of the fiber. The symmetric circular spot size on the target indicates an even energy application. (B) Note the focus of the aiming beam at the point of contact of this contact laser fiber. The laser energy will be concentrated in the same location and will produce an incision in tissue.
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K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
tip, others are also available. Care should be taken so that the shape of the tip is maintained to preserve the desired effect. Fibers are shipped with some type of sculpted or functional end. Normal use causes the tip to burn away. Laser energy applied when the tip is not contacting tissue reduces the life of the tip, because the heat is not dissipated into the tissue. Once the tip is lost, all fibers become free-beam fibers that send a coherent laser beam directly from the fiber’s end. While cutting may still be performed, a deeper than necessary tissue effect is being exerted. Although reshaping a contact fiber tip is possible, the operator becomes responsible for its function. Another method of concentrating the laser energy at the fiber–tissue interface is blackening the fiber tip with a dark marker or charring it in tissue. Fibers routinely come in 400 to 1000 lm diameters. The smaller the fiber diameter, the more flexible the fiber, and the greater the power density at the target site (efficiency of tissue effect for a given amount of laser energy). The larger the fiber, the less flexible, and the greater the area of tissue affected per discharge of energy. Larger diameter fibers can transmit higher energies with less risk of burning in two. Practically speaking, the most clinically useful fiber diameters range from 600 to 1000 lm. Delivery accessories Laser fibers usually must be guided or stabilized in some manner to accomplish a procedure. A surface ablative procedure can be accomplished by merely holding the fiber by hand. Incisive or deeper procedures, however, require an instrument to manipulate the fiber. General surgical surface procedures can be accomplished using a handheld fiber holding ‘‘pencil’’ that secures the fiber (Fig. 4).
Fig. 4. Devices that stabilize or direct laser fibers for surgical procedures. (Top) Hand pencil for general surgical procedures. (Middle) Rigid curved fiber guide for directing the fiber in deeper tissue. (Bottom) Malleable fiber guide can be tailored to fit different situations.
K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
643
Diode laser safety Eye safety The diode wavelength requires safety glasses of optical density of at least 4.5 at 980 or 1064 nm; the same lenses serve for Nd:YAG and the diode wavelengths. Although many diode laser surgical procedures are endoscopic, protective eyewear should still be worn in case a fiber breaks. Even the aiming beams are harmful if they are directed at the eye. Smoke evacuation No laser smoke of any type should be inhaled. In addition to the health hazards, it frequently causes headache and nausea. A powerful smoke evacuator should always be operated at the surgical site. For invasive procedures, suction can be applied at the nearest body opening and through the endoscope biopsy channel, or the laser fiber can be introduced using a suction handpiece as an insertion cannula. Diode laser in general surgery Noncontact laser surgery The purpose of noncontact laser surgery is usually ablation or coagulation of tissue. Ablation effects are the ‘‘disappearance’’ of tissue into the smoke evacuator and result from higher power for shorter periods. Coagulation is characterized by a blanching of tissue and results from lower powers for longer periods. Increasing distance to tissue, or reducing the power, affect coagulation versus ablation. Noncontact surgery generally requires more power than contact surgery because the energy must be transmitted across space and diffuses once tissue is contacted. Noncontact procedures generally begin at 20 W, which complicates procedures with smaller, less powerful machines. Although power densities for a given laser power setting can be increased by using smaller fibers, the spot size of tissue effect is smaller requiring patience to complete the procedure. In addition, continuous wave laser energy application at higher powers may degrade and burn fibers. This problem can be improved by using an intermittent or repeat pulsed mode, which allows the fiber to cool between energy pulses. Contact laser surgery Contact diode laser surgery is generally incisive. Any laser incision requires tension so that the tissue separates as the incision is created. Energy settings below 20 W are adequate for contact laser applications. Compressing the lumen to occlude blood flow with the laser fiber and applying power low enough to coagulate rather than cut (<5 W) can coagulate small bleed-
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K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
ing vessels. Flowing blood creates a heat sink that dissipates laser energy. Vessels of approximately 2 mm or more in diameter should be ligated. The fiber diameter of conical fibers affects its performance for incisive surgery. Using a 600-lm fiber, the conical tip will degrade quickly; however, the smaller diameter fiber maintains a power density that still allows adequate contact cutting. If the laser procedure is close to vulnerable structures, the tip should be carbonized or the fiber should be replaced to maintain energy focus at the tip of the fiber. Using a 1000-lm fiber, the conical tip is critical, because the power density will not be high enough to cut unless the power is turned up significantly as the tip degrades. The visible effect will diminish and require longer exposure to separate tissue; however, the deeper effect is continuing. A useful compromise between fiber diameter and power density must be discovered for every situation. For bare fiber procedures, such as endoscopically applied laser procedures, the stiffness of the 1000-lm fiber may be preferable, whereas in other situations the flexibility of the smaller fiber may be needed.
Endoscopic laser surgery Flexible or rigid endoscopically guided laser surgery is a main reason to own a diode laser. Minimally invasive surgery reduces patient morbidity and cost. Many formerly debilitating procedures requiring hospitalization have been reduced to outpatient visits. Regardless of whether the goal of the procedure is palliative or curative, the quality of the patient’s life is preserved. The procedure can be accomplished by inserting the laser directly through the viewing device or by triangulation of a handheld laser fiber or surgical instrument through an additional portal. The procedure is tailored to fit the situation, and the possibilities are endless. Endoscope Video systems and lasers should be filtered to prevent interference with the image on the monitor when the laser is activated. The laser and endoscope representatives should be consulted before purchasing complementary units. When asepsis is necessary, cold sterilization is used with the endoscopic equipment. For ease of manipulation, the monitor of the videoendoscope should be placed adjacent to the patient, so that the image is the same as if the operator was looking directly into the patient. In a closed cavity, smoke can obscure vision and should be removed by intermittent suction, or the laser cannula can be inserted through a hole in a suction cannula where continuous positive pressure is not important. Smoke may also collect on the lens and require lavage. Because spatter of hot tissue can crack the lens of an endoscope, a respectable distance should be maintained between the patient and endoscope.
K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
645
Flexible endoscopic laser surgery Generally, the smallest diameter endoscope available is the most desirable, because it reaches tighter spaces and is more flexible. Very small endoscopes, however, usually sacrifice features, such as lavage capability or four-way movement, which may compromise surgery. Laser fibers are passed through the biopsy channel of the flexible endoscope to contact the target tissue. The position of the biopsy channel in the field of view impacts vision during contact laser surgery. The most applicable position is ventral to the field of view, so that the fiber can contact tissue while being observed. The next concern is the biopsy channel itself. Quartz fibers may be sharp, or they may break in the channel. Flexible polyethylene (PE) tubing of a diameter to fit the biopsy channel and transmit the particular laser fiber will help protect the tissue from the sharp edges and will also protect the fresh conical tip on the fiber as it passes through the angled insertion port of the biopsy channel. The author has better results if the laser fiber is placed in the proximal few inches of PE tubing, and both are inserted together. The proximal end of the PE tubing should be flame-flared to keep it from disappearing down the channel, and the distal end should be cut to stay flush with the end of the biopsy channel where it cannot be seen through the endoscope. Dualchannel endoscopes allow simultaneous lavage or use of a grasping instrument. The second channel requires a larger diameter endoscope, however, and it makes the end less flexible. The fiber tip should be at least 1 cm into the visible field before the laser is activated. Heat adjacent to the endoscope will crack the lens, melt the lining of the biopsy channel, or melt the PE tubing, which will cause either of the first two injuries. A 5-second delay before retracting the fiber into the channel allows it to cool adequately. If the fiber tip has become crystallized from overheating, it is likely to break inside the channel. A break is better, however, than losing the fiber tip in the patient. The broken tip can be expelled from the PE tubing, outside the patient. Ablation using higher powers may place the fiber at risk of burning within the endoscopic channel itself. The author has prevented this by using the intermittent, pulsed mode on the laser to let the fiber cool between pulses. The technique of endoscopic noncontact laser surgery is straightforward. The energy for ablation or coagulation is adjusted by visual effect while protecting the endoscope. A vessel is coagulated by compressing its lumen with the fiber tip and applying low power (<5 W). For contact surgery, the technique depends on the shape of the fiber tip. The most common sculpted fibers are conical or hemispheric. These tips must be drawn across tissue for incision, because pushing them causes the tip to bury into tissue. Wedged tips can be used in a ‘‘push’’ manner to incise tissue without burying. One disadvantage when the tip is out of sight before withdrawing it toward the endoscope is that the tip may either not be contacting tissue, or it may be contacting some tissue other than the target. The fiber tip rather
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K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
than the side of the fiber should be used for cutting to ensure the most efficient effect. Manipulation of tissue with an instrument may optimize contact between the fiber tip and the tissue. Depending on the location and physical property of the tissue, a stiffer or more flexible fiber may improve the result. Incisions along the long axis of the endoscope require withdrawing into or pushing the laser fiber from the endoscopic channel, whereas incisions across the long axis of the endoscope (in any direction) accentuate movement of the endoscope tip itself. The latter requires much more practice, because both the motion of the endoscope and the contour of the tissue must be accommodated. In addition, the motion must be appropriately stopped to prevent the fiber tip from ‘‘flipping’’ onto another tissue after leaving the targeted surface. Rotation of the endoscope to allow fiber movement along a different tissue dimension may facilitate the procedure. Rigid endoscopic laser surgery Rigid endoscopes may access or explore some cavities better and through smaller access portals than flexible endoscopes. Rigid endoscopes commonly used include arthroscopes or longer cystoscopes or laparoscopes. The laser may be inserted through a channel in the endoscopic cannula parallel to the scope, or it may be inserted through another portal in a triangulation fashion. Some rigid cannulae have fiber deflectors to move the laser tip independently from the endoscope. Where pressure is necessary, the fiber can be inserted in a laser cannula through a stab incision without losing the seal, whereas insertion through a laparoscopic cannula would cause a leak and loss of inflation pressure.
Fig. 5. Brass hooks can be fashioned for tensing or elevating tissue for incision during endoscopic surgery. The size and tip can be tailored for any situation.
K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
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Fig. 6. Grasping forceps are used to elevate, tense, or retrieve excised tissue. (A) The 50-cm instrument can be bent to fit different situations. (B) The jaws can be redirected by carefully bending the shaft of the instrument. It is advisable to minimize bending.
Accessories A few items facilitate endoscopic procedures. Contact laser surgery usually requires some method of providing traction or tension on the tissue. If a simple relieving incision is required, a brass hook can be fashioned to provide tension or to elevate the tissue above underlying structures (Fig. 5). Tissue can be grasped for elevation or retrieval with a long forcep (Universal Grasping Forceps, Richard Wolf Medical Institute, Chicago, IL; Fig. 6). Debulking a larger mass may reduce the time and laser energy required to ablate a mass. Electrosurgical loops can be used to amputate protruding tissue, and the remaining base can be ablated with the laser (Acu Snare Polypectomy Device ASJ-1, Wilson Cook Medical GI Endoscopy, Charlotte, NC; Fig. 7). Baskets for retrieving resected tissue from body cavities eliminate the
Fig. 7. Larger masses can be debulked using an electrosurgical loop, so that the underlying base of the mass can be ablated with the laser. Electrosurgical loop is passed through the biopsy channel of an endoscope to encircle a pedunculated mass before amputation.
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risk of dropping tissue or seeding cells or infection (Endocatch-II disposable specimen pouch, US Surgical Corporation, Mansfield, MA).
Conclusion The diode laser is a useful addition to the surgical laser capabilities of a veterinary practice. Even as CO2 laser waveguides evolve, the diode fiber will continue to be more universally applicable to endoscopic procedures. Its tissue penetration properties affect treatment of deeply situated lesions and its portability is an advantage for surgeons who move from practice to practice. When these considerations are important and only one laser is affordable, the diode unit becomes a strong consideration.
References [1] Dorros G, Seeley D. Understanding lasers. In: Types of lasers. Mount Kisco (NY): Futura; 1991. p. 55–7. [2] Auth DC. Fundamentals of lasers for endoscopy and laser tissue interactions. In: Jensen DM, Brunetaud JM, editors. Medical laser endoscopy. Boston: Kluwer Academic Publishers; Dev Gastroenterol 1990;10:1–15.
Diode laser and endoscopic laser surgery Kenneth E. Sullins, DVM, MS Marion duPont Equine Medical Center, Virginia-Maryland Regional College of Veterinary Medicine, PO Box 1938, Leesburg, VA 20177, USA
Laser equipment Diode lasers are replacing neodymium:yttrium aluminum garnet (Nd:YAG) lasers in veterinary surgery, because they are smaller, more efficient, and more cost-effective because of the semiconductor technology that produces the laser (AOC LaserCare 50, 50-W, solid-state, 980-nm diode surgical laser, Lumenis, Santa Clara, CA; Fig. 1) [1]. Although their applications are similar, commonly used medical diode lasers operate at wavelengths of 810 or 980 nm versus the 1064 nm of Nd:YAG lasers. Because these wavelengths are not in the visible spectrum, aiming beams are used to show the operator where the laser energy will impact target tissue. Diode lasers are commonly marketed in 25- to 60-W configurations. Diode laser–tissue interaction The wavelengths of the diode and Nd:YAG lasers penetrate comparative depths into tissue because they are most absorbed by melanin, hemoglobin, and darker pigments that do not usually occur on the surface. The concentration of these or other darker pigments determines the penetration at a given energy level. Nonpigmented tissue, such as cornea, absorbs none of the energy, whereas a pigmented melanoma absorbs a great deal of the energy. A caveat to this comes with the 980-nm diode laser, which has increased water absorption compared with the 810-nm diode and the 1064-nm Nd:YAG laser, and produces an efficient surface effect (Fig. 2) [2]. Subsurface, nonpigmented tissue, such as myelin, which may ordinarily have been minimally affected by these wavelengths, could be at higher risk with the 980-nm diode laser. Tissue necrosis, hemorrhage, or neuropathy are potential complications. Depth of penetration of the laser energy is a particular concern during endoscopic procedures of hollow organs.
E-mail address: [email protected] (K.E. Sullins). 0195-5616/02/$ - see front matter Ó 2002, Elsevier Science (USA). All rights reserved. PII: S 0 1 9 5 - 5 6 1 6 ( 0 2 ) 0 0 0 1 3 - X
640
K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
Fig. 1. Tabletop 50-W diode laser (980 nm). The unit operates from a standard electric outlet and requires no external cooling source.
Laser delivery Quartz fiber delivery allows function in the noncontact (delivery device does not contact tissue) or contact mode. The tissue effect is determined by the wavelength and power density in the noncontact mode. The noncontact mode is described by the pure definition of light interaction with tissue. The purpose of the contact mode is to modify the raw interaction to achieve a particular effect. Laser fibers usually arrive in sterile packaging or can be sterilized using gaseous or cold sterilization techniques.
Fig. 2. Tissue absorption of common laser wavelengths. Note the relatively good absorption of the diode and Nd:YAG wavelengths in hemoglobin and melanin. The 980-nm diode laser has increased water absorption compared with the 810-nm diode and Nd:YAG lasers. (Modified from illustration provided by Lumenis, Santa Clara, CA.)
K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
641
Fiber types Noncontact or free-beam fibers are squared, cleaved, or polished, so that the coherent light is transmitted directly to the tissue (Fig. 3A). Depending on the power density, these fibers coagulate, vaporize, or ablate tissue. Power density is determined by the fiber size and the energy delivered. Noncontact fibers are used for procedures, such as ablating masses, when underlying tissue is of minimal concern. Tissue may also be coagulated in anticipation of a later slough or to minimize hemorrhage for a subsequent incisive procedure. To preserve optimal function, misshapen or crystallized tips must be stripped of the plastic outer coating and cleaved. The quality of the tip can be judged by the shape and clarity of the aiming beam. Contact fibers are sculpted or shaped to focus (or diffuse) the energy in the desired manner (Fig. 3B). Hybrid shapes, such as a hemispheric fiber, can accomplish some of both the contact and noncontact functions. The most obvious contact function is incision of tissue where the desired effect is at the tissue surface. Depth of the tissue effect is controlled in the contact mode by the shape of the fiber tip. Although the conical tip is the most commonly used contact
Fig. 3. Laser fibers are shaped to produce the desired effect. (A) This noncontact fiber has been cleaved to deliver a coherent laser beam into tissue directly ahead of the fiber. The symmetric circular spot size on the target indicates an even energy application. (B) Note the focus of the aiming beam at the point of contact of this contact laser fiber. The laser energy will be concentrated in the same location and will produce an incision in tissue.
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K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
tip, others are also available. Care should be taken so that the shape of the tip is maintained to preserve the desired effect. Fibers are shipped with some type of sculpted or functional end. Normal use causes the tip to burn away. Laser energy applied when the tip is not contacting tissue reduces the life of the tip, because the heat is not dissipated into the tissue. Once the tip is lost, all fibers become free-beam fibers that send a coherent laser beam directly from the fiber’s end. While cutting may still be performed, a deeper than necessary tissue effect is being exerted. Although reshaping a contact fiber tip is possible, the operator becomes responsible for its function. Another method of concentrating the laser energy at the fiber–tissue interface is blackening the fiber tip with a dark marker or charring it in tissue. Fibers routinely come in 400 to 1000 lm diameters. The smaller the fiber diameter, the more flexible the fiber, and the greater the power density at the target site (efficiency of tissue effect for a given amount of laser energy). The larger the fiber, the less flexible, and the greater the area of tissue affected per discharge of energy. Larger diameter fibers can transmit higher energies with less risk of burning in two. Practically speaking, the most clinically useful fiber diameters range from 600 to 1000 lm. Delivery accessories Laser fibers usually must be guided or stabilized in some manner to accomplish a procedure. A surface ablative procedure can be accomplished by merely holding the fiber by hand. Incisive or deeper procedures, however, require an instrument to manipulate the fiber. General surgical surface procedures can be accomplished using a handheld fiber holding ‘‘pencil’’ that secures the fiber (Fig. 4).
Fig. 4. Devices that stabilize or direct laser fibers for surgical procedures. (Top) Hand pencil for general surgical procedures. (Middle) Rigid curved fiber guide for directing the fiber in deeper tissue. (Bottom) Malleable fiber guide can be tailored to fit different situations.
K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
643
Diode laser safety Eye safety The diode wavelength requires safety glasses of optical density of at least 4.5 at 980 or 1064 nm; the same lenses serve for Nd:YAG and the diode wavelengths. Although many diode laser surgical procedures are endoscopic, protective eyewear should still be worn in case a fiber breaks. Even the aiming beams are harmful if they are directed at the eye. Smoke evacuation No laser smoke of any type should be inhaled. In addition to the health hazards, it frequently causes headache and nausea. A powerful smoke evacuator should always be operated at the surgical site. For invasive procedures, suction can be applied at the nearest body opening and through the endoscope biopsy channel, or the laser fiber can be introduced using a suction handpiece as an insertion cannula. Diode laser in general surgery Noncontact laser surgery The purpose of noncontact laser surgery is usually ablation or coagulation of tissue. Ablation effects are the ‘‘disappearance’’ of tissue into the smoke evacuator and result from higher power for shorter periods. Coagulation is characterized by a blanching of tissue and results from lower powers for longer periods. Increasing distance to tissue, or reducing the power, affect coagulation versus ablation. Noncontact surgery generally requires more power than contact surgery because the energy must be transmitted across space and diffuses once tissue is contacted. Noncontact procedures generally begin at 20 W, which complicates procedures with smaller, less powerful machines. Although power densities for a given laser power setting can be increased by using smaller fibers, the spot size of tissue effect is smaller requiring patience to complete the procedure. In addition, continuous wave laser energy application at higher powers may degrade and burn fibers. This problem can be improved by using an intermittent or repeat pulsed mode, which allows the fiber to cool between energy pulses. Contact laser surgery Contact diode laser surgery is generally incisive. Any laser incision requires tension so that the tissue separates as the incision is created. Energy settings below 20 W are adequate for contact laser applications. Compressing the lumen to occlude blood flow with the laser fiber and applying power low enough to coagulate rather than cut (<5 W) can coagulate small bleed-
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K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
ing vessels. Flowing blood creates a heat sink that dissipates laser energy. Vessels of approximately 2 mm or more in diameter should be ligated. The fiber diameter of conical fibers affects its performance for incisive surgery. Using a 600-lm fiber, the conical tip will degrade quickly; however, the smaller diameter fiber maintains a power density that still allows adequate contact cutting. If the laser procedure is close to vulnerable structures, the tip should be carbonized or the fiber should be replaced to maintain energy focus at the tip of the fiber. Using a 1000-lm fiber, the conical tip is critical, because the power density will not be high enough to cut unless the power is turned up significantly as the tip degrades. The visible effect will diminish and require longer exposure to separate tissue; however, the deeper effect is continuing. A useful compromise between fiber diameter and power density must be discovered for every situation. For bare fiber procedures, such as endoscopically applied laser procedures, the stiffness of the 1000-lm fiber may be preferable, whereas in other situations the flexibility of the smaller fiber may be needed.
Endoscopic laser surgery Flexible or rigid endoscopically guided laser surgery is a main reason to own a diode laser. Minimally invasive surgery reduces patient morbidity and cost. Many formerly debilitating procedures requiring hospitalization have been reduced to outpatient visits. Regardless of whether the goal of the procedure is palliative or curative, the quality of the patient’s life is preserved. The procedure can be accomplished by inserting the laser directly through the viewing device or by triangulation of a handheld laser fiber or surgical instrument through an additional portal. The procedure is tailored to fit the situation, and the possibilities are endless. Endoscope Video systems and lasers should be filtered to prevent interference with the image on the monitor when the laser is activated. The laser and endoscope representatives should be consulted before purchasing complementary units. When asepsis is necessary, cold sterilization is used with the endoscopic equipment. For ease of manipulation, the monitor of the videoendoscope should be placed adjacent to the patient, so that the image is the same as if the operator was looking directly into the patient. In a closed cavity, smoke can obscure vision and should be removed by intermittent suction, or the laser cannula can be inserted through a hole in a suction cannula where continuous positive pressure is not important. Smoke may also collect on the lens and require lavage. Because spatter of hot tissue can crack the lens of an endoscope, a respectable distance should be maintained between the patient and endoscope.
K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
645
Flexible endoscopic laser surgery Generally, the smallest diameter endoscope available is the most desirable, because it reaches tighter spaces and is more flexible. Very small endoscopes, however, usually sacrifice features, such as lavage capability or four-way movement, which may compromise surgery. Laser fibers are passed through the biopsy channel of the flexible endoscope to contact the target tissue. The position of the biopsy channel in the field of view impacts vision during contact laser surgery. The most applicable position is ventral to the field of view, so that the fiber can contact tissue while being observed. The next concern is the biopsy channel itself. Quartz fibers may be sharp, or they may break in the channel. Flexible polyethylene (PE) tubing of a diameter to fit the biopsy channel and transmit the particular laser fiber will help protect the tissue from the sharp edges and will also protect the fresh conical tip on the fiber as it passes through the angled insertion port of the biopsy channel. The author has better results if the laser fiber is placed in the proximal few inches of PE tubing, and both are inserted together. The proximal end of the PE tubing should be flame-flared to keep it from disappearing down the channel, and the distal end should be cut to stay flush with the end of the biopsy channel where it cannot be seen through the endoscope. Dualchannel endoscopes allow simultaneous lavage or use of a grasping instrument. The second channel requires a larger diameter endoscope, however, and it makes the end less flexible. The fiber tip should be at least 1 cm into the visible field before the laser is activated. Heat adjacent to the endoscope will crack the lens, melt the lining of the biopsy channel, or melt the PE tubing, which will cause either of the first two injuries. A 5-second delay before retracting the fiber into the channel allows it to cool adequately. If the fiber tip has become crystallized from overheating, it is likely to break inside the channel. A break is better, however, than losing the fiber tip in the patient. The broken tip can be expelled from the PE tubing, outside the patient. Ablation using higher powers may place the fiber at risk of burning within the endoscopic channel itself. The author has prevented this by using the intermittent, pulsed mode on the laser to let the fiber cool between pulses. The technique of endoscopic noncontact laser surgery is straightforward. The energy for ablation or coagulation is adjusted by visual effect while protecting the endoscope. A vessel is coagulated by compressing its lumen with the fiber tip and applying low power (<5 W). For contact surgery, the technique depends on the shape of the fiber tip. The most common sculpted fibers are conical or hemispheric. These tips must be drawn across tissue for incision, because pushing them causes the tip to bury into tissue. Wedged tips can be used in a ‘‘push’’ manner to incise tissue without burying. One disadvantage when the tip is out of sight before withdrawing it toward the endoscope is that the tip may either not be contacting tissue, or it may be contacting some tissue other than the target. The fiber tip rather
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K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
than the side of the fiber should be used for cutting to ensure the most efficient effect. Manipulation of tissue with an instrument may optimize contact between the fiber tip and the tissue. Depending on the location and physical property of the tissue, a stiffer or more flexible fiber may improve the result. Incisions along the long axis of the endoscope require withdrawing into or pushing the laser fiber from the endoscopic channel, whereas incisions across the long axis of the endoscope (in any direction) accentuate movement of the endoscope tip itself. The latter requires much more practice, because both the motion of the endoscope and the contour of the tissue must be accommodated. In addition, the motion must be appropriately stopped to prevent the fiber tip from ‘‘flipping’’ onto another tissue after leaving the targeted surface. Rotation of the endoscope to allow fiber movement along a different tissue dimension may facilitate the procedure. Rigid endoscopic laser surgery Rigid endoscopes may access or explore some cavities better and through smaller access portals than flexible endoscopes. Rigid endoscopes commonly used include arthroscopes or longer cystoscopes or laparoscopes. The laser may be inserted through a channel in the endoscopic cannula parallel to the scope, or it may be inserted through another portal in a triangulation fashion. Some rigid cannulae have fiber deflectors to move the laser tip independently from the endoscope. Where pressure is necessary, the fiber can be inserted in a laser cannula through a stab incision without losing the seal, whereas insertion through a laparoscopic cannula would cause a leak and loss of inflation pressure.
Fig. 5. Brass hooks can be fashioned for tensing or elevating tissue for incision during endoscopic surgery. The size and tip can be tailored for any situation.
K.E. Sullins / Vet Clin Small Anim 32 (2002) 639–648
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Fig. 6. Grasping forceps are used to elevate, tense, or retrieve excised tissue. (A) The 50-cm instrument can be bent to fit different situations. (B) The jaws can be redirected by carefully bending the shaft of the instrument. It is advisable to minimize bending.
Accessories A few items facilitate endoscopic procedures. Contact laser surgery usually requires some method of providing traction or tension on the tissue. If a simple relieving incision is required, a brass hook can be fashioned to provide tension or to elevate the tissue above underlying structures (Fig. 5). Tissue can be grasped for elevation or retrieval with a long forcep (Universal Grasping Forceps, Richard Wolf Medical Institute, Chicago, IL; Fig. 6). Debulking a larger mass may reduce the time and laser energy required to ablate a mass. Electrosurgical loops can be used to amputate protruding tissue, and the remaining base can be ablated with the laser (Acu Snare Polypectomy Device ASJ-1, Wilson Cook Medical GI Endoscopy, Charlotte, NC; Fig. 7). Baskets for retrieving resected tissue from body cavities eliminate the
Fig. 7. Larger masses can be debulked using an electrosurgical loop, so that the underlying base of the mass can be ablated with the laser. Electrosurgical loop is passed through the biopsy channel of an endoscope to encircle a pedunculated mass before amputation.
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risk of dropping tissue or seeding cells or infection (Endocatch-II disposable specimen pouch, US Surgical Corporation, Mansfield, MA).
Conclusion The diode laser is a useful addition to the surgical laser capabilities of a veterinary practice. Even as CO2 laser waveguides evolve, the diode fiber will continue to be more universally applicable to endoscopic procedures. Its tissue penetration properties affect treatment of deeply situated lesions and its portability is an advantage for surgeons who move from practice to practice. When these considerations are important and only one laser is affordable, the diode unit becomes a strong consideration.
References [1] Dorros G, Seeley D. Understanding lasers. In: Types of lasers. Mount Kisco (NY): Futura; 1991. p. 55–7. [2] Auth DC. Fundamentals of lasers for endoscopy and laser tissue interactions. In: Jensen DM, Brunetaud JM, editors. Medical laser endoscopy. Boston: Kluwer Academic Publishers; Dev Gastroenterol 1990;10:1–15.