Page 28 - Clinical Manual of Small Animal Endosurgery

16 Clinical Manual of Small Animal Endosurgery

Fig. 1.16 A reusable 10 mm trocar-cannula unit. This example has a
pyramidal tip, insufflation port and trumpet valve.

the obturator advances beyond the tip, thus protecting abdominal organs
from injury. Insufflation tubing attaches to the hub of the needle.

Cannulae
During laparoscopy, the telescope and working instruments are intro-
duced into the abdomen via trocar-cannula units (Fig. 1.16). Trocars are
sharp-pointed stylets enclosed in a sleeve (cannula) used to penetrate
fascia and muscles. Once the abdominal cavity has been entered, the
trocar is removed, and the cannula is used to introduce the scope and
instruments. These are freely movable within the cannula, as there is no
locking mechanism.
The presence of a one-way valve prevents gas escape and loss of
pneumoperitoneum during instrument passage; a rubber washer seals the
space between the cannula and the endoscope or instrument when in
place. Most cannulae have also a Luer-lock stopcock for gas insufflation.
Trocar-cannula assemblies can be made of stainless steel (reusable) or
hard plastic. The latter are intended for single use, but can be re-sterilised
a limited number of times. Three trocar-cannula assemblies are typically
required to perform laparoscopic interventions. This number can increase
to four for more advanced procedures. The size of the cannula depends
on the size of the scope and instruments used: the cannula is usually
chosen to be 0.5–1 mm larger than the item inserted through it (com-
monly 6–11.5 mm); reducers are available to permit insertion of smaller
instruments without loss of pneumoperitoneum. Larger cannulae (18–
33 mm) are used to insert particular instruments such as large staplers
and specimen bags. Cannulae can have straight or threaded shafts;
the latter, although more difficult to insert, are more secure, and
minimise the risk of dislodgement during introduction and removal of
instruments.