Page 113 - Clinical Manual of Small Animal Endosurgery

Diagnostic Laparoscopy 101

The flow rate can usually be regulated between 1 and 20 L/min in 0.1 L
increments. At the onset of the procedure insufflation rate should not
exceed 1 L/min to allow the patient to slowly adapt to the increasing
abdominal pressure. Once the desired abdominal pressure is reached the
valve closes, stopping the delivery of gas. At this point the flow rate can
be increased to allow inflation to be maintained despite ongoing leaks.
An automatic insufflation feature will open the valve and restart gas flow
if the intra-abdominal pressure falls below a predetermined value. This
often occurs with insertion and removal of instruments, and particularly
if suction is used.
To prevent a decrease in venous return and reduction in ventilating
ability, intra-abdominal pressure should never exceed 12–13 mmHg in
cats and 13–15 mmHg in dogs. These pressure levels are required for
portal creation, as they allow a safe distance between the abdominal wall
and the underlying structures. After all required portals have been estab-
lished, an intra-abdominal pressure of 8–10 mmHg is usually sufficient
to allow excellent visualisation.
Due to the large potential space of the peritoneal cavity, intra-
abdominal pressure should be very low on the insufflator display at the
beginning of the procedure. If at this point the intra-abdominal pressure
is abnormally high, and all connections are in the open position, incor-
rect positioning of the cannula or Veress needle must be suspected.
Pneumoperitoneum is usually established with a Veress needle. This
consists of a sharp outer trocar and a blunt hollow inner spring-loaded
obturator, which retracts when the needle contacts the abdominal wall.
As soon as the abdominal cavity is penetrated, the blunt inner stylet
advances beyond the sharp tip, minimising the risk of injury to abdomi-
nal organs. The needle is equipped at the end with a Luer-lock adaptor,
to which the insufflation tubing attaches. Veress needles can be dispos-
able or reusable. Reusable needles are always sharp, and require less
force to penetrate the abdominal wall. However, they are rarely used in
veterinary medicine because of their cost. Re-sterilising and reusing dis-
posable needles is possible, but it is not practical, as this would determine
loss of sharpness and therefore defeat the purpose of their use.
Trocar-cannula units are used to introduce the telescope and operative
instruments into the abdomen. They are available in different sizes,
chosen accordingly to the diameter of the scope and instruments used:
the cannula is usually 0.5–1 mm larger than the item inserted through it.
Reducers are available to permit insertion of smaller instruments without
loss of pneumoperitoneum.
Standard units consist of a hollow outer portion (cannula) and a sharp-
pointed stylet (or trocar) protruding from the cannula. The stylet has a
conical or pyramidal tip, and is used to penetrate fascia and muscles.
Pyramidal tips are preferable for insertion in the closed manner, as they
facilitate penetration. Once the abdominal cavity has been entered, the
trocar is removed, and the cannula is used to introduce the scope and
instruments. An automatic valve (a ball valve, trumpet valve or butterfly