Page 114 - Clinical Manual of Small Animal Endosurgery

102 Clinical Manual of Small Animal Endosurgery

washer) seals the cannula when no instrument is present, thus preserving
insufflation pressure.
A rubber washer seals around the instrument shaft when in place. A
Luer-lock stopcock for gas insufflation is also usually present. Trocar-
cannula assemblies can be reusable (made of stainless steel), disposable
or hybrid. These can be re-sterilised a limited number of times. An
advantage of reusable units is that the sleeves are usually made of hard
clear plastic, thus allowing the operator to monitor progress of instru-
ment insertion. In both disposable and reusable units the stylet becomes
blunt with repeated use, and needs to be sharpened. Hybrid trocars can
be a good solution, since they provide for easy replacement of compo-
nents that wear easily. Opening the rubber seal manually when introduc-
ing the trocar also helps to prevent blunting. It is also important to check
that the sharp tip is centrally placed, to avoid damage to the seal, which
will result in gas leakage.
Cannulae are available with straight or threaded shafts: the latter are
more difficult to insert, but the risk of their dislodgement during surgery
is minimal. Innovative cannulae have recently been introduced to mini-
mise the risk of trocar injury: some are equipped with optical viewing
capability (optical trocars). In these trocars a distal viewing lens allows
the light from the laparoscope to be seen, thus enabling the operator to
follow the progress of the trocar during insertion. Other cannulae (Ter-
namian EndoTIP System , Karl Storz) do not require a trocar, and are
®
placed with a twisting motion after a small incision in the abdominal
wall. Three trocar-cannula assemblies are typically required to perform
laparoscopic interventions. This number can increase to four for more
advanced procedures.
Although the essential kit for diagnostic laparoscopy consists of palpa-
tion probes, grasping forceps and biopsy forceps, a vast array of hand
instruments are available, comparable to the ones for open surgery, with
shafts of different lengths and diameters. General characteristics of the
instruments to be considered are:

• the possibility of rotating the shaft and consequently the tip: instru-
ments with an ‘in-line’ configuration allow easier rotation of the
instrument around its axis, whereas instruments with a ‘pistol-grip’
configuration feel more stable in the operator’s hand; the ‘in-line’
configuration is usually preferred for needle holders;

• the possibility of articulation of the instrument shaft; a knob on the
shaft of the instruments causes the tip to angulate up to 90° when
pushed; this reduces the need for additional portals, allowing the
instrument to approach the tissue from various angles;
• the presence of a ratchet that allows the instrument to be locked onto
tissue; this is especially important for grasping forceps, because if the
instrument locks the operator can relax their grip;