uses the CO2 laser in deep areas. The Nd:YAG and diode and some other lasers are commonly delivered endoscopically through much more flexible quartz fibers.
Prevention
Adequate patient sedation is absolutely required. The horse’s willingness to rest the extended head on a support device is a good measure of adequate sedation that should prevent sudden movements that would risk equipment and personnel. Most sedated horses tolerate the procedures very well.
However, quartz is a crystal that can break and should be inspected before every procedure. Overbending/kinking or stepping on the long fibers are common accidents that damage the fibers. After visual inspection, the room lights should be dimmed and with the aiming beam activated, the fiber should be bent in several directions in a bow shape to evaluate for defects in the fiber. Focal or linear bright lights along the fiber show cracks where light (and laser energy) can escape, causing damage to the interior of the biopsy channel and the workings of the endoscope leading to expensive repairs (Figure 12.14a). Damaged fibers are prone to burn out and can severely damage an endoscope (Figure 12.14b). Bare quartz fibers should always be cleaved and stripped for a new procedure. The fiber tips should be clear and the aiming beam should go out the end of the fiber. Frosted or charred tips cause light to diffuse out of the sides or not at all. Worn‐out tips are inefficient and brittle.
Once lased in the patient, the fiber tip remains hot for a few seconds after the generator is turned off; the larger the fiber, the longer it retains heat. By far the most common endoscope accident is retraction of the hot fiber tip back into the biopsy channel or lasing with the fiber tip too close to the end of the endoscope. Experience will teach the surgeon the “proper” length of fiber to work with so tissue is positively contacted while not risking the endoscope. Surgeons must overcome the urge to suddenly retract the hot fiber if the horse moves or something is not exactly right. Working with sufficient fiber length past the end of the videoendoscope also prevents melting the Teflon tubing over the lens or spattering the lens with hot liquefied tissue.
Figure 12.14 (a) Preoperative laser fiber inspection in a darkened room with the aimed beam turned on showing a fiber defect that will certainly burn out and damage the endoscope. (b) Damaged quartz fibers that burn out in the endoscopic channel severely damage the endoscope.
Source: Kenneth E. Sullins.
Plastic coated gas cooled quartz fibers should be inspected in the same manner as bare fibers and gas flow through the tip should be verified. Occluded gas flow results in immediate burn out of the quartz fiber. If a sapphire tip is to be added to the gas cooled fiber, the threads must be inspected so the energy goes out through the tip and not the side. If, during lasing, the metal tip “blows” or “flares up,” it is probably ruined and the metal will have become melted or deformed. The endoscope should be removed from the patient with the fiber in place. If damaged, the tip should be cut off before bringing the fiber back through the scope or the interior of the biopsy channel can be damaged.
Fibers that fit too tightly in the biopsy channel are at risk of overheating and burning out and damaging the interior of the endoscope. In general, 600–800‐micron fibers fit well. Passing bare fibers through a Teflon tubing liner facilitates passage and protects the tip of the endoscope. Gas‐ cooled fibers should pass through with no trouble.
Summary
Surgical lasers broaden and deepen surgical possibilities to the advantage of patients and owners and new applications continue to appear. As long as the surgeon understands laser physics and tissue interaction and exercises a few straightforward precautions, the results will be pleasing for all involved.
Reference
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