An introduction to laser endosurgery

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The term 'laser' is actually an acronym, standing for Light Amplification by the Stimulated Emission of Radiation. The first workable experimental laser, a pulsed ruby laser, was developed in 1960 by Theodore Maiman. A basic knowledge of optical laser physics is useful in understanding the clinical applications of laser energy. This chapter provides a brief introduction to laser physics relevant to veterinary practice. The most commonly used laser in veterinary medicine is the carbon dioxide laser. These efficient, economical and highly effective lasers are excellent for general surgical use. However, the underlying physics of these lasers means that their use in endoscopic applications is limited. This chapter discusses Instrumentation; Mass resection; and Transurethral laser lithotripsy.

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14.1 Atoms resting in a ground state of energy. When bombarded with electrons (electricity), atoms move from a ground state to a singlet state of energy. When excited, atoms drop from the singlet state to the metastable state of energy. This change in state results in the loss of energy in the form of a photon. If a photon collides with a metastable atom as it is dropping to the ground state (which invariably happens), energy is lost in the form of a photon. ⤳ = Photon.
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14.2 Laser optical chamber. The power supply pumps energy, in the form of electrons, through the lasing medium. There is a fully reflective surface at one end of the chamber and a partially reflective surface at the other end. The release of the photons within the chamber produces a bright, intense, high-energy monochromic light.
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14.3 Diode laser equipment. (Courtesy of Diomed Ltd)
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14.4 Flat bare fibre non-contact laser tip.
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14.5 Laser fibres.
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14.6 Optical fibres. Sculpted fibre tips. Top: Conical tip. This is used for precise, delicate procedures requiring a fine incision. Bottom: Orb tip. This is used for a broader incision in vascular tissue. Contact and non-contact fibres. Top: Bare flat-end fibre. This is used for both contact and non-contact procedures. Bottom: Non-contact fibre (water- or air-cooled). This is used for gastroenterology and pulmonary applications. (Courtesy of Diomed Ltd)
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14.7 Tissue interaction with non-contact fibres. Light emitted at 810–900 nm is highly absorbed by haemoglobin and melanin, and generates high temperatures at the tissue surface. This results in rapid vaporization with underlying coagulation of up to 3 mm. The effects of high power (left) and low power (right) on the surrounding tissue. (Courtesy of Diomed Ltd)
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14.8 Nasal mass resection.
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14.9 Pre-, intra- and postoperative images of laser resection of a colonic adenocarcinoma. Note the use of a right-angled fibre. The beam leaves at a right angle to the long axis of the fibre.
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14.10 Intra- and postoperative images of laser resection of a urethral transitional cell carcinoma. Not the use of a sculptured pointed tip fibre, allowing the surgeon to perform more delicate tissue vaporization.
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14.11 Lateral abdominal radiograph of a spayed 10-year-old Miniature Schnauzer bitch with radiopaque densities in the caudal abdomen. To confirm the location, size and contour of the abdominal radiopaque densities, a double contrast cystogram was performed. The dark structures in the centre of the urinary bladder are urocystoliths. Cystoscopic view of uroliths in the lumen of the bladder after initiation of laser lithotripsy. A 365 μm diameter flexible quartz laser fibre is positioned near the surface of the urolith, creating a crater in the stone. Double contrast cystogram after transurethral lithotripsy and voiding urohydropropulsion to remove urolith fragments. The radiograph is consistent with complete urolith removal. Urolith fragments. The uroliths were composed of 100% calcium oxalate.
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14.12 Lateral abdominal radiograph of a neutered 9-year-old male Labrador Retriever with radiopaque uroliths in the distal urethra. A Foley catheter was positioned with its balloon proximal to the urethroliths. Inflating the balloon prevented the urethroliths and urolith fragments from migrating into the urinary bladder during lithotripsy.
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