الفهرس 
ANATOMY OF THE CENTRAL
The brain ventricular systemOnly 14 pages are availabe for public view
 |  | from | 16 |  |  |
| | | from | 16 | | |
Abstract
Neurologic complications are second only to heart failure as a
cause of morbidity and mortality following cardiac surgery.
Neurological complications are more common among patients
undergoing surgery with (CPB), especially complex surgery,
involving aortic valve replacement, surgery of multiple valves, or
involvement of aortic surgery.
Neurological injury can be defined as any temporary or
permanent injury to the nervous system.The nervous system is
divided into two parts: the central nervous system (CNS), which
consists of the brain and the spinal cord, and the peripheral
nervous system.
The adult human brain receives 12% to 15% of cardiac
output and the cerebral blood flow is approximately 50 mL/100
g/min. The brain‘s metabolic requirements must be met by
adequate delivery of oxygen and glucose.
The arterial blood supply to the brain is composed of
paired right and left internal carotid arteries, which give rise to the
anterior circulation, and paired right and left vertebral arteries,
which give rise to the posterior circulation. The connection of the
two vertebral arteries forms the basilar artery.
The internal carotid arteries and the basilar artery connect
to form a vascular loop called the circle of Willis that permits collateral circulation between both the right and left and the
anterior and posterior perfusing arteries.
Many mechanisms regulate cerebral blood flow, including
chemical, myogenic, and neurogenic factors. But CPB is typically
associated with alteration in these mechanisms, changes in body
temperature, hematocrit, mean arterial pressure and loss of
pulsatility causing a predictable effect on cerebral perfusion
which may induce cerebral injury.
Most neurologic problems following cardiac surgery can
be divided according to the American College of Cardiology and
the American Heart Association into Type I outcomes which
includes the stroke, stupor and coma, and Type II outcomes which
include the affection of the intellectual function and memory.
Different mechanisms are thought to be responsible for
early onset or intraoperative neurological insult including cerebral
hypoperfusion, embolization and systemic inflammatory
response.
Also patient-specific risk factors such as prior stroke or
transient ischemic attack, advanced age, diabetes, hypertension,
aortic atherosclerosis, plays a role in perioperative neurological
insult.
Neuromonitoring during CPB helps to maintain adequate
cerebral perfusion and early detection of ischemic or embolic
events, for early application of cerebral protective mechanisms such as hypothermia, drugs for reduction of cerebral activity and
metabolism for reduction of further damage.
Neuromonitors includes transcranial doppler to monitor
blood flow velocity in the middle cerebral artery and also allows
quantification of the number of emboli transiting the middle
cerebral artery, near-infrared spectroscopy (NIRS) a non-invasive
technique of monitoring oxygen saturation in a small part of the
frontal lobes, electroencephalography (EEG) and bispectral index
(BIS) which can detect cerebral ischemia, since the frequency and
amplitude of spontaneous cortical electrical signals decrease when
cerebral blood flow falls to critical levels.
Other strategies for management of neurological injury
during CPB include proper preoperative evaluation, improving
cerebral oxygen balance by maintaining MAP between 50 and 80
mmHg during CPB, retrograde or antegrade cerebral perfusion
during hypothermic circulatory arrest, proper temperature and
acid–base management, red cell transfusion to maintain adequate
levels of Hct, and blood glucose control.
All these mechanisms work together to provide a better
neurological outcome, reduction of postoperative hospital stay
and providing a better life improvement following cardiac
surgery.