Читать книгу Complications in Equine Surgery - Группа авторов - Страница 188

General surgery using lasers consists of primary incisions, excision of masses followed by primary closure or leaving the wound open for second intention healing, and ablation/vaporization of tissue or masses also left open for second intention healing. Incisions intended for primary closure are sensitive in that skin margin viability must be preserved. Appropriate power density, rate of laser movement and separating tissue tension prevents collateral heating of the skin margins that could lead to marginal skin slough and incisional dehiscence. Carbon dioxide lasers are the best choice for these types of general surgery because tissue can be precisely incised with almost no collateral heating with appropriate instrument settings and surgical technique. The approximate appropriate power density expecting primary healing for a skin incision is 5,000 W/cm² [10].

If either of these is in question, sutures set back from the skin margins 2–3 extra millimeters could help prevent dehiscence.

The Nd:YAG /diode laser is not as precise as the CO₂ laser for skin incisions. The quartz fibers or sapphire tips produce more collateral heating of tissue. The power should be set high and the handpiece advanced in a single pass with skin tension separating the margins as it progresses. Tension relieving sutures provide some insurance against marginal necrosis of tissue. Noncontact delivery of the Nd:YAG/diode laser produces too much collateral heating for reliable primary tissue healing and can risk subsurface tissue.

Either of the above lasers can be used for excision of masses where skin margins are not a concern. However, the CO₂ laser is more efficient for large masses and there are no fibers to wear out. Where important structures lie deep close to the surgical site, the near infrared lasers should be restricted to contact delivery.

While all laser surgery removes some tissue along the lines of incision/dissection, ablation/vaporization removes all the target tissue by non‐contact delivery of laser energy. Masses ablated/vaporized are usually comparatively small or they would have been excised. Examples include smaller dermal melanomas, squamous cell carcinomas or similar masses. Limited to noncontact delivery, the CO₂ laser ablates tissue efficiently and safely, because it is highly absorbed by water and tissue penetration is limited. Still, surrounding tissue collateral heating should be minimized. The computerized scanner described earlier greatly increases efficiency and reduces collateral heating. Nd:YAG/diode lasers efficiently ablate dark‐colored soft tissue masses but can still over penetrate to deeper tissue. Contradicting the opening sentence, a spherical sapphire tip on a gas‐cooled fiber of an Nd:YAG laser can be used to perform “contact ablation” by “painting” the lesion away similar to a burr on bone. Importantly, the sapphire tip largely limits the effect to the surface. Only heat is delivered to the tissue so collateral heating must be watched but deeper penetration of laser energy will be limited.