Cognitive dysfunction
Cognitive dysfunction occurs after cardiac
operations at a rate estimated as high as 80% in the acute phase after surgery
and may persist in 20% to 40% of cases depending on length of follow-up.
However, in adults between 1.5 and 3.2 % of
patients sustain a stroke during heart surgery using CPB and between 3 and 25%
have significant cognitive impairment at 1 year (Roach 1996; Taylor 1998).
In children undergoing open heart surgery the
incidence of acute neurologic complications is around 2.3 to 6% (Fallon 1995;
Menache 2002).
Emboli
Microemboli are defined as particles less than
500 microns in diameter.
Air entry into the perfusion circuit produces
the most dangerous gas emboli because nitrogen is poorly soluble in blood and
is not a metabolite. Carbon dioxide is rapidly soluble in blood and is
sometimes used to flood the surgical field to displace air. Foreign emboli,
largely generated in the surgical wound, reach the circulation from the
surgical field via the cardiotomy reservoir. The cardiotomy reservoir is the
primary source of foreign emboli and the major source of blood-generated
emboli, particularly fat emboli. Extensive activation and physical damage to
blood elements produce a wide variety of emboli, which tend to increase with
the duration of perfusion.
In-depth or screen filters are essential for
cardiotomy reservoirs and are usually used in arterial lines. The efficacy of
arterial line filters is controversial since screen filters with a pore size
less than 25 to 40 microns cannot be used because of flow resistance across the
filter. Moreover, air and fat emboli can pass through filters and air and
atherosclerotic emboli may enter the circulation downstream to the filter.
