LASER is the acronym for Light Amplification by Stimulated Emission of Radiation.
A laser is a device that generates an intense beam of light that can cut, seal or vaporize tissue. It is different than the light around us in several ways. The most important difference is that laser light consists of one wavelength while the light around us is composed of many different wavelengths. The light of a laser is created by energizing molecules to emit light at a certain wavelength. There are many different kinds of laser, each of which operates at a unique wavelength. Three examples of popular lasers are the carbon dioxide (CO2), Nd:YAG, and Diode.
The CO2 laser is one of the most widely used lasers in the world. It operates at a wavelength of 10,600nm. When a CO2 laser is delivered to the soft tissue, the light energy is absorbed by the water existing in the soft tissue. This then heats up the soft tissue and vaporizes it. The CO2 laser is used for its ability to spare surrounding tissue from heat damage and its precise cutting.
The Nd:YAG laser (1064 nm) is delivered through a small quartz fiber which allows it to be used through a videoendoscope. The endoscope is a long flexible tube with a camera on the end that allows the doctor to see into areas that he could not see otherwise, for example deep within the nasal passage. Thus, the laser can be transmitted down a fiber through an endoscope and used deep within the nasal passage (Figure 1). The light energy from this laser is absorbed by two major components of living tissue: melanin, the dark pigment in skin and hair; and, hemoglobin, the pigment in red blood cells that carries oxygen. The Nd:YAG laser is more readily absorbed by tissue than the CO2 laser leading to better coagulation (blood clotting), but the increased absorption leads to increased thermal damage to surrounding tissues.
The diode (wavelength 980 nm) laser has become increasingly popular in large animal surgery since it has a very similar wavelength to the Nd:YAG and therefore can also be delivered via a small quartz fiber through a videoendoscope. The advantage over the Nd:YAG is that the diode laser is small, portable, and more efficient.
Laryngeal Hemiplegia (roaring):
The most common surgical treatment is a prosthetic laryngoplasty or a “tieback” procedure. This procedure involves permanently opening one side of the throat to avoid it from collapsing into the airway under the negative pressure as the horse breathes in. If the throat were to collapse, there would be an obstruction and abnormal respiratory noise (roaring).
A common adjunctive therapy is the removal of the vocal folds and/or the laryngeal saccules that stabilize the bottom portion of the arytenoid cartilage in the airway to decrease the abnormal noise and increase the airway diameter for possible increased performance. This technique has been traditionally performed through an incision in the throat region (laryngotomy) under general anesthesia after the “tieback”. The laser can be used to perform a similar procedure but can be achieved in the standing horse (or under general anesthesia) through the endoscope (Figure 2). This obviates the need for a surgical incision.
Traditional surgical correction involves splitting the tissue down the middle (axial division) with a curved blade or surgical resection through an incision in the throat region (usually under general anesthesia). Laser division of the tissue can be performed using either the Nd:YAG or diode laser through the videoendoscope. This technique can be done on an outpatient basis (with the patient sedated and using local anesthesia) with decreased surgical complications and reduced healing time (Figure 3). The re-entrapment rate is also slightly lower with the use of a surgical laser versus a traditional surgical approach.
Treatment consists of removing the mass and the tissue of origin. With small masses that arise from the ethmoid region, this can be accomplished by injection of the mass with formalin under standing sedation. This process may need to be repeated several times. For large masses, a sinus bone flap under general anesthesia may be necessary.
Laser ablation of the mass can be achieved through an endoscope in the standing horse. This procedure can be done after formalin or sinus flap surgeries or by itself with small masses. The use of the laser decreases both hemorrhage during surgery and the chance of recurrence of the mass.
Guttural Pouch Tympany or Empyema:
Guttural pouch tympany is a condition that occurs in foals. The exact cause of the condition is unknown but most agree that there is a malfunctioning of the mucosal flap in the pharynx that forms an opening to the guttural pouch. Instead of allowing air to flow in and out of the guttural pouch, the flap acts as a one-way valve, allowing air in but not out. Thus, air gets trapped in the pouch and excessive air accumulation in the pouch leads to tympany. Foals affected with this condition have a large, non-painful swelling on one or both sides of the throat latch region. Diagnosis is based mostly on clinical signs.
In the conventional approach, an opening is created between the two guttural pouches through a surgical incision in the throat latch region while the foal is under general anesthesia. Using a laser, this same opening can be created; or an opening between the affected pouch and the pharynx can be created. By using a laser, either of these surgeries can be performed through the videoendoscope on an outpatient basis with the foal standing under sedation (Figure 4).
Dorsal Displacement of the Soft Palate:
Upper Respiratory Tract Cysts and Masses:
Endometrial cysts within the uterus of a mare can be treated with laser surgery. Using hysteroscopy, or videoendoscopic guidance, the laser can be used to ablate/remove these fluid-filled structures while avoiding trauma to the surrounding uterine lining or the remainder of the reproductive tract. This surgery can be performed in the standing sedated mare with the use of local anesthesia.
As surgical techniques continue to advance, the laser will be used to treat an increasing number of diseases. Additional uses of lasers include:
- breaking up bladder/urethral stones
- removing cartilage hock joints to aid in fusing a joint (facilitated ankylosis) for treatment for chronic arthritis of the distal hock joints or the pastern joint.
- sealing of blood vessels during laparoscopic procedures to prevent hemorrhage
Laser Surgery versus Conventional Surgery
- Less Bleeding: the laser seals small blood vessels during surgery
- Less Swelling: decreased bleeding and no crushing of tissues decreases postoperative swelling
- Shorter Hospitalization Times: many procedures can be done with standing sedation and therefore, the horse does not require general anesthesia. This reduces the risk of complications as well as hospitalization time.
- Precision: the laser can be controlled precisely to remove thin layers of tissue
- Minimally Invasive: the laser can be used through an endoscope to allow access to tissues deep within the body without making additional incisions to allow conventional access to these tissues (throat or uterus).
- Less Pain: the laser seals nerve endings as it cuts therefore, the patient experiences less pain
- Sterilization: the laser sterilizes the surgical site (kills bacteria) as it cuts
- Faster Recovery: a decreased amount of bleeding and swelling will result in faster healing of tissue. This will lead to a faster return to activity and use.
Laser Surgery versus Conventional Surgery
- Requires specialized equipment and training
- Can result in excessive thermal damage and swelling to adjacent or target tissue if not used appropriately
Laser surgery is a specialized technique of performing surgery. The great advantage of laser surgery in large animals is that it allows your surgeon access to deep areas and tissues so that they may perform surgery through a minimally invasive approach with and without general anesthesia, depending on the lesion and its location. Outcome and prognosis depends on the type and location of the lesion treated. If you have any questions about laser surgery, you should contact an ACVS board-certified veterinary surgeon.