Page 49 - Clinical Manual of Small Animal Endosurgery

Diagnostic Arthroscopy 37

Fig. 2.5 Fenestrated cannula with trocar. A fenestrated cannula is
particularly useful for stifle arthroscopy, when soft tissue can partially
occlude the cannula; hence, multiple fluid-egress points are useful.

past the scope tip, ensuring the view is not compromised by particulate
matter or haemorrhage, which is flushed away from the scope tip. To
create fluid flow through the joint a constant outflow or egress is required.
Without good egress, the fluid entering the joint tends to extravasate into
the periarticular soft tissues and this progressively prevents fluid disten-
sion of the joint cavity, reducing the intra-articular space until the view
is totally compromised. For small joints, a large-bore (22 gauge or larger)
needle provides a suitable egress but for the shoulder joint, and certainly
for the stifle joint, a fenestrated egress cannula is necessary for uninter-
rupted fluid outflow (Fig. 2.5). Efficient fluid flow requires a head of
pressure and for small joints this can be achieved using a simple fluid
compression bag in which the pressure is maintained with a hand pump
(Fig. 2.6).With this system the fluid pressure and therefore the flow rate
tend to be variable and erratic. Fluid pumps provide better-controlled
pressure and therefore improved fluid flow. Pumps give precise control
over intra-articular pressure and fluid flow rates, normally prioritising
pressure over flow rate. Most pumps function using a peristaltic roller
mechanism, giving accurate control of pressure delivery, which is gener-
ally set at between 40 and 100 mmHg. A fluid pump gives improved
clarity of vision throughout arthroscopic procedures and this tends to
reduce the duration of surgery (Fig. 2.7).
When high volumes of fluid are used, a collection system is useful to
contain the wet area in the procedure room/operating theatre. Waste
fluid can be directed via flexible tubing attached by Luer-lock to the
egress cannula/needle into a collection bag or waste bowl. Alternatively,
waste fluid may be allowed to flow onto an impervious patient drape
and then to the floor, where it can be scavenged using a floor suction