100 QUESTIONS IN CARDIOLOGY

considered severe. What is more difficult is how they translate

into the patient’s everyday life. This is dependent upon the nature

of their activities. A cardiac surgeon who suffered a 20% decline

in their fine motor movements would undoubtedly have a severe

disability. In contrast a road sweeper would not suffer unduly, at

least in their work. The tests customarily performed in this area

are most useful as a window onto surgery rather than showing an

impact on quality of life.

Can they be prevented?

The mechanisms for neuropsychological decline are considered to

be multifactorial. The most popular explanation for cognitive

dysfunction is microemboli delivered to the brain during surgery.

These can be either air or particulate (atheromatous matter, fat,

platelet aggregates, etc.) in nature. In an attempt to reduce the

incidence of neuropsychological decline various interventional

studies have been designed. Much of this work has centred on the

impact of different equipment and techniques used in surgery on

neuropsychological outcome. Early studies comparing bubble

and membrane oxygenators indicated a higher frequency of

microemboli detected when using bubble oxygenators with

decreased neuropsychological deficits occurring in the membrane

group. Studies have also found that the introduction of an arterial

line filter into the CPB circuit significantly reduces the number of

microemboli detected at the middle cerebral artery during CABG.

A significant reduction in neuropsychological deficits in the filter

group has also been reported. In contrast a study comparing

pulsatile and non-pulsatile flow found no difference in neuro-

psychological outcome between the two techniques.

As the use of hypothermic perfusion during CPB has been based

on the protective effects of low temperature in limiting the effects

of cerebral ischaemia it is surprising that studies so far have failed

to find any advantage for hypothermic bypass on neuro-

psychological outcome. Two studies have examined the impact of

pH management on cognitive performance and both have reported

benefit from using the alpha stat technique. Less disruption to

autoregulation has also been reported in the alpha stat group.

More recently pharmacological neuroprotection has been

attempted in these patients with a variety of compounds. Most of

these studies have been underpowered and only one appears to

have produced some suggestion of neuroprotection.