الفهرس 
Anatomy of the Central Nervous SystemOnly 14 pages are availabe for public view
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Abstract
N
eurologic 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.