Laser Surgery in Small Animal Practice

As with most anything in life, even in veterinary medicine ever-changing technology is rapidly pulling us into the 21st century. No longer are the cool “toys” limited to the veterinary institutions and the multimillion-dollar referral practices. Recent graduates are entering the work force with advanced training. Printed media, animal programs on cable TV and the INTERNET are educating clients on the advances in veterinary medicine. The result – practitioners need to keep up!

Traditional medicine has taught the use of the scalpel, or cold steel. The scalpel is still the gold standard for surgical incisions, but, as with anything, it has its limitations.

Cold steel was replaced by the “electroscalpel.” For many years this radiosurgery was the standard in exotic animal medicine. Now, in the dawn of the 21st century, the laser (Light Amplification by the Stimulated Emission of Radiation) has emerged as a viable alternative to surgical intervention.

Introduction

Cold steel surgery, even with the best technique, has the risk of excessive hemorrhage. This problem was somewhat controlled when the electroscalpel was introduced.

Radiosurgery, the successor to the standard scalpel, offered many options and solutions to hemorrhaging problem seen in the small exotic patients. Radiosurgery involves the passage of fully filtered, fully rectified, high-frequency radio waves through tissue. This technique causes cutting of the tissue with minimal coagulation.

Electrosurgery, by definition, involves the removal or destruction of tissue by conversion of energy into heat through tissue resistance to the passage of high-frequency alternating current. The radio waves here are fully rectified but not filtered. As a result, the unit effectively cuts and coagulates.

Electrocoagulation involves the use of a partially rectified, intermittent flow of high-frequency current to seal blood vessels. It is not intended for incisions.

Electrocautery involves the heating of a needle tip or scalpel using low frequency, high amperage current. This is not a form of electrosurgery since no radiowaves pass through the patient. This term is often erroneously interchanged with the aforementioned elecrocoagulation.

A big concern with Radiosurgery techniques is the problem with lateral transfer of heat to surrounding tissue. Lateral heat damages tissue and ultimately delays healing and encourages dehiscence.

Since the operator has the ability to control laser’s output and focus the laser’s beam, these problems can be circumvented. There is no contact between the laser and the patient’s tissue. All of these factors contribute to making the laser ideal for surgical cases in exotic animal medicine.

Laser Physics

The idea of Lasers has been around since the early 1900’s when Einstein proposed the concept of stimulated light emission. Theodore Maiman developed the first laser in 1960. Weapons research, communications and manufacturing technologies provided the impetus to further laser research. After the end of the Cold War the laser manufacturers, looking for additional applications of their product, began the push for laser involvement in industry and medicine.

A standard light bulb and a laser share one thing in common - they both generate electromagnetic energy – commonly called light. The electromagnetic spectrum extends from very short wavelengths (gamma radiation at 10 -11 m) to radio waves (10 -1 m). The laser wavelengths fall between infrared and ultraviolet, which include the invisible and visible (400 – 700 nm) light spectrum.

The power behind a laser comes from its ability to store energy in atoms, concentrating the energy and releasing it in the form of powerful waves of light energy. Specifically, an atom in its resting ground state in a given medium (e.g. solid crystal, liquid or gas) becomes excited to a higher energy state by absorbing thermal, electrical or optical energy. After the energy is absorbed, the atom spontaneously returns to its resting state by releasing that energy as a photon – this is called Stimulated Emission.

This released photon resonates between mirrored ends of the laser chamber, further exciting other atoms in the laser medium. The momentum of the particles grows until finally a highly concentrated beam of light passes through a partially transmissive mirror at one end of the laser chamber.

Just as sound passes through air, or a ripple in the water, light travels in waves. Frequency is the term for the number of waves that pass a point in time. The frequency of light (known as the number of oscillations per second) combined with its wavelength (the distance between one peak to the next) determine the color of light. Normal white light is INCOHERENT, which means it contains many wavelengths radiating in all directions. If you shine a flashlight into a prism the beam is broken down into its different colors.

Laser light, in comparison to normal light, is COHERENT, and consists of only one color, known as MONOCHROMATIC. The last distinguishing feature of laser light, is that it is COLLIMATED, or non-radiating as is white light. Laser light travels in parallel beams, each reinforcing the beam next to it.

The wavelengths of medical lasers range form 193 nm (UV-excimer lasers) to 10,600 nm (farinfrared lasers). Only lasers in the wavelengths of 400 – 700 nm are visible to the naked eye.

The laser in science fiction is always red in color. Medical lasers that are visible to the eye are the Argon laser (blue – 488 nm), the YAG or KTP laser (green – 532 nm), the Dye laser (yellow/orange/red – 577 – 665 nm) and the Ruby laser (deep red – 694 nm). The Carbon dioxide laser, the most commonly used laser in veterinary medicine, is in the non-visible range (10,600 nm).

Laser light must be converted to another form of energy to produce its therapeutic effects. Laser interactions are categorized according to whether laser energy is converted into heat (photothermal), chemical energy (photochemical) or acoustic (mechanical-photodisruptive) energy.

When laser light is absorbed by a cell, the water within the cell is boiled and the cell essentially explodes. The cell denatures into smoke and the cell remnant, called char. This smoke, which has been documented to contain DNA, bacteria and viruses, should always be evacuated with a filtered vacuum.

When utilizing a small laser tip. The cellular destruction is limited to a region only three to four cells away from the target area, thus minimizing tissue devitalization, thus making laser incision far less destructive than either cryosurgery or electrosurgery.

Types of Lasers in Small Animal Practica

There are many different types of lasers used in the medical field. The two most commonly used in Veterinary Medicine are the Diode laser and the Carbon Dioxide Laser. Either of these instruments is usually chosen for a specific purpose in mind, such as dermatological or endoscopic applications.

Carbon Dioxide (CO2) Laser

This laser type has long been used for its ability in tissue ablation. The 10,600 nm wavelength is highly absorbed by water, making it ideal for cutting (with a focused beam) and vaporizing (using a defocused beam) tissue.

Cutting with the CO2 laser is virtually bloodless in most capillary beds as it seals vessels less than 0.6 mm in diameter. Lymphatics are also sealed, reducing post-operative edema. Smaller nerves are sealed as well, and perhaps even spared, resulting in less pain for the patient. Since the tip of the laser does not contact the skin or tissue being incised (as does the tip of a radioscalpel), microorganisms are destroyed in the process of photothermal ablation. Most importantly, the thermal insult from a given amount of energy is superficial, only 50 – 100 um in depth.

Diode Laser

Diode lasers can vary in wavelength from 635 – 980 nm. These lasers have been used for photocoagulation of retinal and other ocular tissues since 1984.

A big advantage of diode lasers is their ability to be used in conjunction with the fiberoptic delivery systems (i.e. through an endoscope). Additional uses of diode lasers include chromophore enhanced tissue ablation or coagulation, laser welding (tissue fusion) and photodynamic therapy.

The diode laser has deeper penetration than the CO2 laser, and thus is less precise for delicate procedures such as debriding a cornea and ablating a right adrenal gland.

All lasers cut with a high intensity beam of light. These light beams can be focused at a specific distance. This allows the surgeon to use this intensified light beam to "cut" tissue when focused, or, “ablate” the tissue, when defocused.

A simple analogy can be made with using a magnifying glass in the sunlight. The convex glass collects the sun's beams or rays and focuses them to a pinpoint. The light rays can be focused to a fine point by moving the magnifying glass closer or further away from the surface being imaged. The beam is at its peak intensity when the point of light is at its smallest diameter. This correspondingly is also when the beam of light is at its maximum cutting power - which can be easily demonstrated by focusing the sun beam on a piece of paper and watching it burn with exacting precision.

The laser works in a similar fashion. It actually cuts tissue by searing through it with a highly intense focused beam of generated light. Just like the magnifying glass, the laser has to be positioned so that it is focused on the target tissue (the growth or tumor, for instance).

“Ablation" is especially useful for removing small growths or tumors (such as a ferret adrenal gland). In some situations it is preferable to "ablate" the tumor rather than cut it off. What this means is that the laser beam is defocused on the tumor, and instead of cutting it away, the laser literally disintegrates it.

Making the Cut

There are three factors that determine the impact of the delivered laser beam: spot size, power and exposure.

Spot size refers to the diameter of the aperture that contains 86% of the laser’s beam. The tip size of the handpiece (commonly 0.4 or 0.8 mm) and the distance of the tip from the target tissue determine the actual spot size at the target. For most applications this is typically 1 mm.

Power is measured in watts, which is defined by the amount of energy applied over time (defined as Joules/second). Power is adjusted on the laser by adjusting the wattage. The greater the wattage, the higher the power.

Power density is affected by the size of the target area. If the spot size is small, the power is concentrated. If the spot size is large, the power is spread out over a larger area, and the power density is decreased, thus producing a lessor tissue effect.

Exposure is also a user controlled variable. Exposure is determined by the duration of the applied laser. The greater the exposure, the greater the tissue impact. Exposure can be delivered as continuous, repeat or single pulse. Surgical precision is increased respectively.