Page 112 - Clinical Manual of Small Animal Endosurgery

100 Clinical Manual of Small Animal Endosurgery

the need for an outer sheath; the cannula is sufficient to guarantee scope
protection, and operative channels are not useful because of their limited
diameter. Different viewing angles affect the visualisation of the operative
field: although scopes with 0° viewing angle are the simplest to use, their
field of view is the most limited. By rotating an angled telescope on its
axis, the surgeon can obtain a wider field of view, which is very useful
for examination of relatively inaccessible areas and for allowing more
room for instrument manoeuvring.
However, spatial orientation with angled scopes is more challenging,
and the instruments enter the field of view at different angles from what
intuitively expected. To obtain a more ‘anatomical’ orientation, the light
cable is held upwards, so that the angled view is facing down. A 30°
viewing angle – a good compromise between size of the field of view and
ease of spatial orientation – is usually preferred. Recently, a telescope
has been devised which allows the possibility of changing the angle of
view at the turn of a dial situated at the proximal end of the telescope
®
(EndoCAMeleon , Karl Storz GmbH and Co. KG, Germany).
A high-intensity (300 W) light source is recommended for laparoscopy,
because of the need to illuminate a large cavity. The dark surfaces in the
abdomen (liver, presence of blood) will also absorb light (Magne and
Tams, 1999). Xenon light sources are preferred as they are considered to
better reproduce the colours of the abdominal organs. If a less optimal
light source is to be used, such as halogen, it is important to choose a high-
quality camera, which will require less light (Magne and Tams, 1999).
For laparoscopy the endoscope is connected to a video camera, which
sends the images to a monitor. This not only allows the operator to work
more comfortably and to benefit from the help of assistants, but results
in a superior image of the operating field, and is crucial for maintaining
sterile conditions.
In order to visualise abdominal structures and interpose some space
between the trocar-cannula units and the abdominal organs, an optical
space needs to be created by insufflating the abdominal cavity with gas.
Air is not advised for this purpose, as it could easily cause embolism;
nitrous oxide is soluble in blood and could be employed, as long as
energy-assisted devices are avoided, because nitrous oxide is highly com-
bustible and spark ignition could occur. The gas most commonly used is
carbon dioxide, which is non-combustible and readily absorbed in blood.
These characteristics make carbon dioxide a safe choice, with very low
risk of gas embolism, and not dangerous even when using energy-assisted
devices. A minor disadvantage with carbon dioxide is the formation of
carbonic acid on contact with peritoneal surfaces, which causes discom-
fort in the postoperative period (Magne and Tams, 1999).
Carbon dioxide is delivered by a dedicated insufflator. This is a com-
puterised pump which controls gas flow rate and total volume of gas
delivered, and maintains abdominal pressure at a preset value. The insuf-
flator display also shows the total amount of gas delivered during the
procedure, and the remaining pressure in the carbon dioxide cylinder.