Fundamentals Of Laser Surgery For The Beginner To Intermediate Surgeon
Jim Irwin, DVM
Every discussion involving the usage of surgical lasers requires an endorsement
of important safety issues. All medical lasers require users to strictly
adhere to safety policies. While manufacturers usually have many built in
safety features, the mere lack of familiarity by doctors and staff to laser
equipment in general contributes to an overall safety concern. Since accidents
can be catastrophic, ample attention should be given to the development
and enforcement of safety polices. Assigning a staff member as laser safety
officer and having a periodic review of safety policies should be practiced.
Included in the discussion will be a few brief comments about critical safety
issues. Safety issues that all laser users should address:
A focused hand piece, common on CO2 lasers, provides the surgeon the ability to regulate the energy delivery to the target tissue by moving closer to the tissue (focused) for higher power density delivery or moving away from the tissue (defocused) for lower power density delivery. Higher power densities are most effective for cutting or rapid ablation of tissue. Lower power densities are useful for slower, more controlled ablation or for warming tissue to cause collagen shrinkage. The surgeon should grip the hand piece near the tip by using fingertips in a similar fashion as holding a ballpoint pen. However, the hand piece should always be held in a perpendicular position to the target tissue.The CO2 laser is absorbed by the water in the cells of the target tissue, instantly boiling the intracellular water and ultimately destroying the cells of the target tissue leaving behind a carbon, or char, residue. This char should be gently wiped away after each pass with sterile saline. Care should be taken to not apply laser energy onto char from a previous pass as this will heat the char. This heated char may then cause thermal damage to adjacent tissues. The technique thus becomes “lase then wipe, lase then wipe” and so on. Failure to adequately wipe away char will impede healing while wiping too vigorously may remove the caramelized layer that is important for wound sealing and hemostasis. Controlling the amount of char formation is an important consideration for the intermediate level user. While char may be helpful for hemostasis it may also contribute to collateral thermal damage causing post-operative edema and possibly tissue sloughing. An example might be the primary skin incision where hemorrhage is not a major concern. For cleaner, faster skin incisions the surgeon should increase the power density by either increasing the power setting or by decreasing the spot size. This will allow a faster hand movement that ultimately will decrease collateral thermal damage. Some laser equipment is equipped with a super-pulsed mode that allows for extremely short, yet powerful bursts of laser energy. Here is where the skin thermal relaxation time becomes a factor. Briefly, the thermal relaxation time is the time necessary for the target tissue to dissipate heat by fifty percent. In this super-pulsed mode the target tissue has adequate time to cool thereby preventing char formation yet permitting higher power settings. This in turn, allows for faster, char free cutting. Basic Surgical Techniques There are two major uses of the CO2 laser. The surgeon may cut (incise, or resect) or ablate (vaporize).
1. Cutting technique: The cutting action involves making serial passes applying contra-lateral traction or tension with each pass. The number of passes needed is dependent upon the power setting and the speed of the surgeon’s hand movement. The laser seals blood vessels smaller than 0.6 mm in diameter. This technique is useful for most standard soft tissue incisions, and most useful for resecting malignant tumors.
The intermediate level user will soon discover that the tissue tension greatly facilitates the cutting action. This is also apparent when making elliptical excisions where simply elevating and retracting the apex of the elliptical opening will greatly speedup the excision. Elevating and applying tension on the cut edge of an incision provides similar results when undermining or dissecting with the laser. Proper tip selection and power settings are important to optimize the outcome. For finer cutting, a finer tip is used such as 0.3 mm or 0.4 mm tip. The coarser (and somewhat more durable) 0.8 mm ceramic tip may be used when a wider cut is acceptable. A sufficient power setting should be selected that will cut though tissue at a comfortable rate of delivery for the user. Moving too slowly can cause thermal damage to adjacent tissue. Moving too rapidly will not provide proper cutting or hemorrhage control. As skill develops, the user will eventually be able to make a full thickness cut with one pass and maintain good hemorrhage control and yet not cause significant thermal damage to adjacent tissues. Cautious beginners tend to select low power settings and utilize slow hand movement. This actually contributes to more thermal damage to the patient, slows healing and perhaps causing post-operative pain.
2. Ablation technique: The ablation action involves “painting” the surface of the target tissue with a single lasing then wiping away the charred remains. With each pass the target tissue is gradually vaporized away. This ablation technique is useful in removing certain tumors, lick granuloma, feline stomatitis, and chronic otitis. For ablation a wider tip, such as a 0.8 mm or 1.4 mm tip, is optimal. The energy delivery rate should be adequate to quickly vaporize the target tissue and not cause thermal damage to adjacent tissue. Again user skill will dictate actual power settings. If a biopsy is required the surgeon should first debulk the mass by excision and then ablate the remaining tissue.
Many procedures involve using more than one surgical modality. Examples include using laser for skin and subcutaneous tissues and then using scissors for tough ear cartilage, or using a scalpel blade to cut delicate urethral mucosa. Laser technology should be used where it is most applicable and beneficial to the patient.
Tips for better end results:
Common Laser Soft Tissue Procedures
The following procedures will utilize the basic technique as outlined above. Exceptions to the basic technique and specific concerns will be discussed.Mild entropion: Mild cases can be treated by lightly ablating the skin below the lid to cause collagen shrinking and resultant correction of the lid inversion. This ablation (also called XXX technique) is effective for the lower lid only. This technique will not be effective for situations that are significantly rolled inward or in cases that have redundant lid tissue. First make a continuous pass along the lower lid staying approximately 1 mm from margin. Use a 1.4 mm tip at 2 to 3 watts. Then create a row of “Xs” in the skin of the lower lid. The laser heating action on the collagen should shrink the redundant lid and the results should be noticeable immediately. There are no sutures employed in this procedure.
Moderate to severe entropion: The majority of the entropion cases will be in this category. These will require standard skin excision with suturing. Laser offers the advantage of profound hemorrhage control. It is the author’s opinion that the employing CO2 laser in excising redundant lid tissue should be performed in a more conservative manner (take less) than using cold steel. There will be some laser-induced collagen shrinkage occurring with this excision procedure and this shrinkage may cause the surgeon to over-correct the entropion. Care should be taken to cut deep to the orbicularis oculi muscle to prevent lid muscle action post-operatively. Suture wound with 4.0 swaged-on suture material.
Epulis removal: The fibrous epulis can be effectively removed with ablation technique. While most epulides are of the fibrous type careful examination should be undertaken to verify that the epulis does not involve underlying bone. An acanthomatous epulis, which involves underlying bone, will likely require more aggressive treatment (excision and radiation therapy). Extreme care is taken to not cause thermal injury to the adjacent tooth structure. The epulis mass is carefully retracted away from the base of the tooth. The bulk of the mass may then be excised in routine fashion. The remaining portion should be carefully ablated. The beam should be directed parallel (not perpendicular) to the surface of the tooth. The epulis is ablated with the 1.4 mm tip at 6 –8 watts continuous power. Multiple passes are taken to carefully remove all traces of the epulis. There will be a black recessed area evident at completion of the procedure. No suturing is necessary.
Stenotic nares: The stenotic nares can be enlarged cosmetically with CO2 laser. A 0.3 mm tip is used at 3 watts continuous power to excise a “wedge” from the mid to lower portion of the dorsal lateral nasal cartilage. The lower-most tip of the dorsal lateral nasal cartilage is not removed. The wedge defect is sutured with 4.0 absorbable suture. Hemorrhage control is excellent and post-operative complications are minimal to non-existent. Sutures will dissolve or be rubbed off by the animal after ten to twelve days. This procedure may often be combined with resection of the elongated soft palate.
Enlongated soft palate resection: The soft palate can easily be shortened with the laser. There are no sutures necessary and there is no bleeding. Extreme caution should be taken to prevent the laser beam from striking the oxygen-rich endo-trachial tube. Aluminum foil tape may be used to cover the tube in the proximity of the procedure. Wet gauze may also be helpful but strict attention should be made to its position, as it often gets moved during the procedure. Care should also be taken to prevent the animal from inhaling the plume. Smoke evacuation should be used continuously during the procedure. The soft palate resection tool (Lumenis AccuVet Lasers, Boston MA) is utilized for best results. This tool simply holds the pendulous portion of the soft palate and provides a backstop for the laser beam. It also has a port for the attachment of the plume evacuator. The excision should extend from a point just below the tonsilar crypt from one side of the oral pharynx to the other side. In larger animals the redundant soft palate tissue is thick and may require using retraction to adequately position it for excision. A suture placed through the lower-most portion of the palate will aid in retraction. An attempt should be made to use high power settings such as 12 to 14 watts at continuous wave setting. The goal is to make a clean, continuous cut with out repeatedly retracing the original pathway. Repeatedly lasing over the first incision will cause excess thermal damage which may appear as edema of the remaining tissue. The procedure is very quick and patients can be released after recovery from anesthesia.
Lick granuloma: A lick granuloma can effectively removed without creating a wound to close with sutures. A 1.4 mm tip is used at 8- 10 watts continuous power. Multiple passes are used with standard wiping (described above). The granuloma is serially ablated until the center and edges are as thin as the normal adjacent skin. Avoid over treatment. There are no sutures necessary and there are no medications dispensed. A light bandage may be helpful to prevent licking for the first 24 - 48 hours as the skin settles down.
Feline onychectomy (the 4 Cut Declaw): Declawing is
performed with laser cutting technique. There are not tourniquets used
as the technique is devoid of hemorrhage. The toes are prepped and individually
stretched to allow for easy cutting. A 0.3 or 0.4 mm tip are used at 6
–8 watts continuous power. There are basically four cuts that are made.
The first cut is across the dorsal surface proximal to the unqual crest.
Skin tumors, considerations: Skin tumors should be evaluated prior to making a decision on surgical technique. The findings of fine needle aspiration, combined with knowledge of gross appearance, size, location, duration, breed, age, and sex may provide a diagnosis. The diagnosis, combined with owner expectations, and overall health of the patient will likely point to a suitable surgical technique, e.g., Simple ablation, excision, or wide excision, or wide excision followed by chemotherapy and/or radiation therapy. Once surgery is undertaken a representative section is collected and submitted for histopathology. It is helpful to perform an in-house impression smear from the section that can be later compared to the histopathology report received from the reference lab. Final histology results may indicate going back and performing a more radical excision in some cases.
Small benign skin tumors (papillomas, basal cell tumors, sebaceous adenomas, histiocytomas, and others) may be simply ablated and not sutured. A 0.8 or 1.4 mm tip at 3 to 5 watts continuous wave is usually effective. If histopathology is to be performed on the mass a portion should be first excised. The remaining mass should then be ablated down to the level of the skin. Then, by pinching the skin on either side of the mass the remaining deeper portions of the tumor may be successfully removed. Carefully inspect the wound margins for any tumor tissue that may have been missed. Once satisfied that all the mass has been removed it is most helpful to shrink the opening by simply defocusing the beam for one additional pass. The opening will then likely be about fifty percent smaller. It is not necessary to wipe the char created by this last pass.
Mast cell tumors, melanomas: The surgeon should exercise great care in examining the patient for multiple sites and systemic signs when dealing with Mast cell tumors and melanomas. Mast cell tumors should never be ablated, again calling attention to the fact that the surgeon should always thoroughly know what he or she is cutting. Cytology or biopsy must be accomplished first. Melanomas should be excised with margins appropriate to the location. Smaller margins may be acceptable in situations that are generally considered as benign such as the hairy torso or eyelid. But larger margins are always necessary in areas where melanomas are considered as more dangerous such as the mouth, digits, or nail beds. Melanoma excision may even require amputation in the case of the digit. Attention to the excision margins and follow-up histopathology on margins and associated lymph nodes are important.
Breast tumors: After appropriate case work-up breast tumors can be efficiently removed with CO2 laser. A 0.8 tip at 8 to 12 watts continuous wave is usually most effective. As always, careful planning of the excision area should first be performed to allow for skin closure. Once incision pathway is planned the surgeon should make one careful pass outlining the entire soon-to-be-excised tissue. Once the skin has been incised full thickness the surgeon should grasp and elevate one end of the pedicle and begin the removal process. With continuous tension being applied to the free end of the pedicle it is removed by a back and forth sweeping action severing the tissue at the subcutaneous level. Hemorrhage control is achieved by defocusing the beam as needed. Larger vessels will need ligatures. Laser excision seals many lymphatic vessels as well as blood vessels. This feature allows for placing fewer subcutaneous sutures and using fewer or no drains for breast strips.