Cardiopulmonary bypass technologies - Biomaterials and Devices for the Circulatory System - page 147

of pre-operative risk assessment was later adapted to compare prospec-
tively the effi cacy of surface coating across patient risk strata with the docu-
mentation of indicators of systemic infl ammation, coagulofi brinolytic activ-
ity as well as biomaterial evaluation. Clear effi cacy of surface coating in
high risk cases even on clinical outcome has been demonstrated and surface
coating can be used in high risk cases that need additional support during
surgery. The CPB market is also very close to reaching a point of saturation
where there will be no additional expense to use coated circuits.
The Society of Thoracic Surgeons published its 'Perioperative blood
transfusion and blood conservation guidelines' in 2007 and indicated that
coated bypass circuits (either the oxygenator alone or the entire circuit)
were not unreasonable for blood conservation in cardiac operations (level
of evidence B). 18

6.5.2 Circuit miniaturization

Miniature CPB addresses several aspects of extracorporeal support with
the aim of making a signifi cant clinical impact. There is a trend in modern
practice of CPB towards reducing the biomaterial surface area exposed to
blood and to reducing circuit priming volume. This trend stems from
improvements in perfusion technology and a desire to minimize the per-
ceived negative effects of haemodilution and blood-biomaterial contact-
mediated infl ammatory processes. 19 In keeping with the minimized
concept, the fi rst generation has not included satisfactory specifi c de-airing
features. Recent products seem to overcome air handling problems. Novel
circuits are supplemented by integration of a venous de-airing unit, which
consists of an ultrasonic air bubble detector, a 150 cm 3 /170 mm bubble
trap and an electronic venous line occluder. The static prime volume of
the system is approximately 800 cm 3 . When air is detected, an automatic
command is given to the centrifugal pump to reduce speed to 1500 rpm,
which is a coasting speed, creating neither forward nor reverse fl ow.
Automatically the venous line is closed in response to the speed reduction
of the centrifugal pump (Fig. 6.4). This allows for controlled manual de-
airing of the bubble trap using a standard vacuum suction device
(

￿ ￿ ￿ ￿ ￿

200 mmHg). 20
By the addition of extra safety features and auxiliary hard shell reservoir
to return conventional system in case of emergency, it has been possible to
adapt minimized circuits to any type of operation (Fig. 6.5). Setting up a
minimized circuit programme requires good planning, cross-discipline work
and cooperation. Miniature cardiopulmonary bypass is by no means the
fi nished article. It is a step towards more physiological extracorporeal
support, combining individually proven modifi cations. Market force is also
a good advantage for the development of this idea.

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