Page 32 - Clinical Manual of Small Animal Endosurgery

20 Clinical Manual of Small Animal Endosurgery

mechanical vibrations. Ultrasonic (harmonic) devices (e.g. Harmonic
Scalpel, Ethicon) have different tissue effects depending on pressure
exerted, activation time, blade speed, blade configuration and power
level. Four different actions (cutting, coagulation, coaptation and cavita-
tion) can be achieved singularly or in combination with one another. In
surgical procedures, all of these effects are typically applied consecu-
tively. Before activating the blade, a combination of tension and pressure
is used to rapidly stretch tissue. When the tissue reaches its elastic limit,
the blade or device tip is able to cut smoothly through it. The blade
usually vibrates 55 500 times per second, and the mechanical energy
produced when it comes into contact with the tissue breaks hydrogen
bonds, defragmenting the protein in the cells (coaptation). This mechani-
cal energy propagates in the direction in which force is applied, with
minimal collateral thermal damage. When ultrasound energy is applied
to tissues a few seconds longer than it takes to achieve coaptation, a rise
in temperature leads to the release of water vapour and then denatura-
tion of protein. The denatured protein forms a coagulum, which seals
the compressed blood vessels.
Cavitation occurs when the rapid vibration of a harmonic device is
transmitted to the surrounding tissue, causing cell disruption and vapori-
sation of intracellular water at body temperature. This leads to separa-
tion of the tissue planes in advance of the blade, which enhances visibility
and allows careful dissection. As with electrosurgical vessel-sealing tech-
nology, the capital cost of the generator and the high cost of the dispos-
able handpieces limit the application of this technology in animals.

Powered instrumentation
Power-operated instruments for arthroscopy consist of motorised blades
(shavers) and burrs, available in multiple sizes and shapes. These power
instruments are used to remove cartilage, bone and soft tissues. Dispos-
able blades are available, which can be reused six to eight times in vet-
erinary patients (until no longer sharp). All the powered instruments are
cannulated to allow suction of the debris produced by the cutting action
of the instrument out of the joint. The most useful sizes in veterinary
medicine are 2.0–4.0 mm.

Operating-room requirements

Whereas some procedures involving rigid endoscopy (notably rhinos-
copy, otoscopy, tracheoscopy and urethrocystoscopy) can be performed
in a non-sterile setting, surgical procedures such as arthroscopy, lapar-
oscopy or thoracoscopy should only be performed with proper aseptic
technique, and in an operating room. In fact, the operating team must
be ready to convert the minimally invasive approach to an open proce-