Biomedical Engineering Reference
In-Depth Information
Leukocyte fi ltration during CPB was initially tested experimentally in the
early 1990s and subsequently used in humans undergoing cardiac surgery.
Filters were incorporated in series into the CPB circuit in the majority of
trials but have also been used to deplete the blood cardioplegic solution or
even in retransfused residual blood after CPB.
Leukofi ltration in cardiac surgery is a good example of a concept that
has not yet been universally adopted due to equivocal results from various
small-scale studies. Many of these demonstrated that leukocyte depletion
contributed to early post-operative improvement in heart and lung function
but did not infl uence signifi cantly the overall clinical outcome of patients
undergoing elective cardiac surgery. This may be due to timing and duration
of the fi ltration procedure and fl ow and pressure conditions in the fi lter.
Another concern is the simultaneous removal of platelets that may affect
post-operative haemostasis. 21
Leukocyte fi ltration was introduced for the purpose of enhancing extra-
corporeal fi ltration beyond conventional gaseous microemboli, aggregate
and particulate to selectively fi lter activated leukocytes, but methodological
discrepancies remained within the literature. Two perfusion protocols have
evolved for the use of leukofi ltration: 'continuous' - throughout the extra-
corporeal circulation - and 'strategic' - during the rewarming phase. The
strategic method involves bypassing the leukocyte fi lter up to the fi nal
10-30 min before removal of the aortic cross-clamp and for the duration of
CPB beyond this point. Clinical support for this technique arises, theoreti-
cally in an attempt to maximize fi ltration effi ciency at the suspected peak
point of leukocyte activation and for avoidance of fi lter pressurization,
which has been reported in the literature. The continuous leukofi ltration
concept is based on the fact that cellular activation has been active at the
outset of surgical intervention with median sternotomy, aortic manipulation
and initiation of CPB. 22 The total leukocyte control strategy is to fi lter white
blood cells in all blood products delivered to the patient (Fig. 6.6).
Considering these discrepancies, Gunaydin et al. compared the clinical
outcome of leukofi ltration on coated and uncoated extracorporeal circuits
with the documentation of indicators of infl ammation, platelet function as
well as biomaterial evaluation in 2005 on 40 patients with multi-vessel coro-
nary artery disease undergoing elective coronary artery bypass grafting. 23
Patients were allocated into four groups, ten patients each. Each group
included fi ve patients with normal pulmonary function and fi ve with docu-
mented chronic lung disease. The results of this study, I believe, demonstrate
the increased effi ciency of leukocyte fi lters when used with coated circuits
simultaneously and especially in patients with critical pulmonary function.
Surface coating was benefi cial in controlling platelet damage.
This provided us the idea of studying leukocyte fi ltration in 225 patients
undergoing coronary artery bypass grafting. 24 Patients were allocated into
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