Page 31 - Clinical Manual of Small Animal Endosurgery

Rigid Endoscopy 19

Fig. 1.18 Diode laser with flexible insertion tube suitable for endosurgery.
Photograph courtesy of Mr P.J. Lhermette.

such as gases (carbon dioxide, helium, argon), crystals (usually neody-
mium:yttrium-aluminium-garnet or Nd:YAG), liquid dyes or diode
semiconductors. The energy absorbed by atoms of the lasing medium at
the passage of light is emitted as photons of a wavelength characteristic
of that medium, which in turn strike other atoms, and so on. The result
is a laser beam of a characteristic wavelength, which is focused in a set
direction by the use of partially reflective mirrors: the light is thus con-
centrated and released in a coherent and powerful manner.
In the animal tissues, substances (called chromophores) absorb laser
light, thus generating heat; these include water, haemoglobin and other
pigments, each absorbing light in a specific portion of the electromag-
netic spectrum. For instance, lasers emitting light at the wavelength
absorbed by water will heat and vaporise tissues with high water content.
Carbon dioxide, diode (Fig. 1.18) and Nd:YAG lasers are the most
commonly used surgical lasers. Carbon dioxide lasers emit light that does
not penetrate fluids well, and is therefore used for cutting and vaporisa-
tion of surface lesions. Diode and Nd:YAG lasers instead penetrate fluids
very well, and can be used for precise cutting and coagulation of deeper
tissues. Consequently, they are preferred for veterinary endoscopy. Addi-
tionally, diode lasers can be directed to the surgical site through flexible
fibre-optic shafts, which makes them more practical for endoscopic
application. Diode lasers are particularly useful for resection of soft
tissues during rhinoscopy and urethrocystoscopy.

Ultrasonic haemostasis and tissue division
Ultrasonic waves are created by applying electromagnetic energy to
a piezoelectric transducer, usually located in the handpiece. These
ultrasonic waves travel from the handpiece to the blade, producing