by Alexis H. Kim, MD, G. David Adamson, MD, FRCS, FACOG, FACS
The development of operative laparoscopic techniques to treat various gynecologic diseases previously treated by laparotomy has been greatly facilitated by the application of lasers. The control and precision of lasers has allowed the performance of advanced operative laparoscopy with relative safety and ease. The use of lasers, however, in the setting of expanded indications for endoscopic treatment of disease, introduces the risk of complications from the operation of the laser and injury to pelvic structures due to the treatment of more advanced disease.
A thorough understanding of the operation, characteristics, tissue effects, and limitations of lasers is required for their safe and effective use. While complications cannot be completely eliminated, they can be significantly reduced by proper technique, good judgement, and proper instrumentation. Attention to the details of laser safety is imperative as the complexity and scope of laparoscopic surgery expands. The safe use of lasers will allow the surgeon to perform increasingly sophisticated surgery and to optimize the care of patients.
CHARACTERISTICS OF LASERS
The type of laser used during laparoscopic surgery can be selected based upon the wavelength of the laser light. The carbon dioxide (CO2), argon, and neodymium:yttrium-aluminum garnet (Nd:YAG) lasers have different properties due to the different absorption characteristics of the wavelengths unique to each laser (Table 1). The potassium deuterium phosphate (KTP532) laser which is produced by halving the wavelength from a Nd:YAG crystal has a 532 nm wavelength which is similar to the argon laser in wavelength and properties. The CO2 laser is the most precise laser but is limited in its coagulating ability. The argon laser has less precision but improved coagulating ability. The best coagulation properties and least amount of precision is found in the Nd:YAG laser.
Laser energy can be delivered via a “touch” or “no touch” technique. The CO2 laser utilizes the “no touch” technique with the beam usually delivered through the operating channel of the laparoscope in order to free the surgeon's hand for use of other instruments. This is advantageous in minimizing tissue trauma due to manipulation and possibly in facilitating dissection in areas not easily accessible. The CO2 laser also can be used at any distance from the tissue with a fairly constant tissue effect. The “touch” technique is used with the fiber lasers such as the argon, KTP532, and Nd:YAG where the laser beam is focused at the fiber tip. The power density is reduced significantly as the fiber tip moves away from the tissue, thus enabling the surgeon to vary the power density. The fiber also can bend to transmit energy to difficult-to-reach areas and has limited smoke production since tissue is not vaporized.
The reaction of tissue to lasers is different depending upon the wavelength (Figure 1). In general, the CO2 laser produces an area of injury that is discrete and reproducible with a depth less than 1 mm and a zone of thermal necrosis less than one-tenth of one millimeter (Figure 2). Thus, the CO2 laser is highly precise but a poor coagulator.
In contrast, the wavelength of the Nd:YAG laser is associated with significant forward scattering of the photons when contact with the tissue is made. As a result, the Nd:YAG laser produces a thermal effect several millimeters below the tissue surface, conferring excellent coagulating ability but poor precision. This property of the Nd:YAG is potentially dangerous if the underlying tissue heats and explodes, producing a "popcorn effect." Reduced thermal injury and a more predictable tissue effect has been achieved with the use of sapphire tips or sculpted fibers. The argon and KTP532 lasers have similar tissue effects between those produced by the CO2 and Nd:YAG laser.
Tissue effects may also vary depending upon the power density of the laser. The power density is directly proportional to the power in watts and inversely proportional to the square of the beam diameter.1 Thus, in general, a small spot size will produce greater penetration and destruction of tissue over a smaller area compared to a large spot size which produces a larger, shallower lesion.
LASER INJURY AND SAFETY
In a review of 821 operative laparoscopies for varying indications, CO2 laser injuries accounted for only 1.2% of the laparoscopic injuries.2 The low frequency at which laser injuries occur during laparoscopic procedures was observed in another study looking at CO2 laser complications during different gynecological procedures.3 Due to the ability of lasers to deliver high energy on contact or from a distance, safety revolves around a thorough understanding and awareness of the potential ramifications of the properties of lasers.4 The risk of injury can be minimized by following the particular guidelines for safety for each laser.
The eye is one of the most susceptible areas of the body to serious laser injuries. It is most sensitive to wavelengths in and near the visible spectrum. The Nd:YAG, argon, and KTP lasers (visible and near-visible laser energy) can burn the retina, whereas the CO2 laser (far-infrared energy) can cause corneal burns. The eye is particularly susceptible to retinal burns from the Nd:YAG laser because the light is invisible and does not induce a protective blink response. Eye protection consists of tinted eyewear for the Nd:YAG, argon, and KTP lasers, and clear plastic or glass eyewear for the CO2 laser. The tinted eyewear filters the wavelength of the specific laser for which it is designed while allowing as many of the other wavelengths to pass in order to maximize visibility. Everyone in the operating room, including the patient, should wear protective eyewear during laser use.
Inadvertent laser burns may occur to the operator, assistant, or patient inside or out of the operating field. One mechanism of injury is the redirection of laser energy from reflective surfaces. The unintentional burning of organs in the patient or burning of the surgeon may occur due to reflections off of surgical instruments. Although the surface of most surgical instruments have a convex curve which usually causes divergence of laser light after reflection, even a small bend radius may appear as a flat surface to a 0.2 mm laser spot. Small pits or dents may also develop on instrument surfaces that potentially could refocus laser energy.
During laparoscopy, the primary risk of injury by reflection is to the patient’s intra-abdominal structures due to the closed nature of surgery and short separation distances of neighboring sites. Several methods of reducing the risk of injury from this potential hazard have been developed especially for the CO2 laser. All of these methods attempt to minimize reflection by scattering the laser beam or absorbing stray energy. This is accomplished by instruments that are finely wire-brushed, sand-blasted, or glass-beaded. If these instruments are to be used as backstops, titanium metal is preferred over stainless steel or instruments with ebonized coatings. Stainless steel does not handle heat as well as titanium, resulting in a tendency to break down over time. Moreover, localized heating may occur, creating a potential for thermal burns upon contact. Ebonized coatings absorb incident laser energy and markedly reduce reflections, but also cause the instrument to heat, predisposing tissue to possible secondary burns. These coatings degrade with each laser impact over time and can flake. Thus, ebonized instruments are not appropriate for use as a laser backstop.
Another cause of inadvertent laser burns is due to human error. These inadvertent burns of varying degrees of severity have been reported with the CO2 laser at the time of laparotomy, although the risk for these injuries also exists during laparoscopic procedures.3 The incidence of these types of burns is dependent upon teamwork, operator experience, and eye-hand-foot coordination. For the CO2 laser, the HeNe aiming beam should always be visualized prior to firing the laser. Moreover, since a blind area near the end of the laparoscope exists, the risk of inadvertent injury to organs, primarily bowel, can be significantly reduced by following this precaution. Although bowel injuries may occur, the occurrence of laser injury is rare. Most bowel injuries are a result of mechanical trauma.5 For contact lasers, the tip should always be visualized, especially immediately after firing the laser since the tip remains hot and can burn surrounding structures.
Injury occurring from the accidental activation of the laser when not in use may occur, especially if another foot pedal is used for a different instrument such as a bipolar electrosurgical instrument. A momentary lapse in concentration or focus on a particular aspect of the operation may result in pressing the laser pedal unintentionally. Although more inconvenient, placing the laser on standby whenever not in use will reduce the risk of injury by this mechanism.
Materials within the surgical field potentially can be ignited by the laser. The liberal use of irrigating solutions to moisten lap packs, gauze bandages, and drapes in the surgical areas reduces the risk of accidental ignition. Flame-retardant surgical drapes for laser surgery are also available. These two precautions, however, may not completely eliminate the risk of ignition.3 Liberal use of irrigating fluids in the pelvis and abdomen adds extra protection during endoscopic procedures. The use of alcohol and ether solutions should be avoided due to their flammable nature. Anesthesiologists should be informed that flammable anesthetic gases are to be avoided as well. While oxygen is not a flammable gas, the choice of concentration should be made carefully since oxygen supports the combustion of other flammable materials. As a precaution, plastic materials or accessories to be used in the surgical field should be tested to ensure that the plastic melts rather than ignites.
Despite adhering to the appropriate precautions, the risk of injury is not completely eliminated. Complications may arise as a consequence of operating in anatomically difficult areas or upon severe disease which can distort anatomy. Ureteral injury with the CO2 laser has been reported despite prior hydrodissection of the peritoneum for the purpose of creating a backstop.6 Laser injury of the ureter, however, is rare with most injuries involving the use of electrocoagulation.7 Identification of the course of the ureter should be attempted, ideally at the beginning of surgery when visualization is best, in order to minimize the risk of injury. Bladder perforation and loss of the sapphire Nd:YAG laser tip are other laser-related complications that have been previously reported.8 These injuries are a “calculated risk” of operating with lasers and are dependent to a large extent upon operator experience.
A less direct, but more common, source of injury associated with lasers involves inadvertent bumping into laser arms (for example, with the head) and tripping over power lines to lasers and other instruments in the operating rooms. Such injuries have been reported and can be serious. Attention to detail with respect to positioning of equipment is important, as is care in moving around an operating room full of numerous additional pieces of equipment.
DIAGNOSIS OF INJURY
Following extensive laser dissection in the cul-de-sac, the bowel should be checked for perforation injuries. This may be performed by placing a 30 cc Foley catheter into the rectum and clamping the bowel above the site of dissection. The pelvis is then filled with physiologic solution and a 50% solution of betadine injected through the Foley catheter. Trailers of betadine solution indicate perforation. Alternatively, air may be injected by a 100 cc syringe and observation for bubbles undertaken. When the nature and extent of injury is discovered, the appropriate management should be undertaken.
If ureteral injury is suspected, indigo carmine (5 cc) can be injected intravenously. The appearance of indigo carmine coloring should be present in the Foley catheter and bag within approximately 10 minutes. As with the detection of bowel injury, underwater trailers may be present if injury to the ureter has occurred.
Postoperatively, if signs and symptoms suggest ureteral injury, the diagnosis may be confirmed by an intravenous pyelogram. Ureteral injury should be suspected by the presence of flank, abdominal, or pelvic pain associated with fever, elevated white blood cell count, and peritonitis which usually occurs within 2-3 days postoperatively.
Vascular injuries in the pelvis are usually readily apparent at the time of injury. In order to determine the adequacy of hemostasis, the pneumoperitoneum may be released for three minutes by the clock. The abdomen is then insufflated and the pelvis checked for bleeding. This technique may also be used to detect small but persistent bleeding in the area of dissection.
Laser use during laparoscopy is a useful and generally safe tool for the treatment of gynecological diseases. Lasers have allowed sophisticated surgery to be performed, in some instances, with better results than could be obtained with laparotomy or other laparoscopic techniques. By virtue of the nature of lasers, as well as the increased complexity of surgery for which lasers are often used, the risk of injury must be carefully considered. A complete understanding of laser use and safety will minimize the risk of injury and allow the surgeon to optimize its application in the laparoscopic treatment of disease.
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