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Arterial circulation The arterial cerebral circulation is normally divided into anterior cerebral circulation and posterior cerebral circulation. There are two main pairs of arteries that supply the cerebral arteries and the cerebrum: Internal carotid arteries and vertebral arteries. The anterior and posterior cerebral circulations are interconnected via bilateral posterior communicating arteries. They are part of the Circle of Willis, which provides backup circulation to the brain. In case one of the supply arteries is occluded, the Circle of Willis provides interconnections between the anterior and the posterior cerebral circulation along the floor of the cerebral vault, providing blood to tissues that would otherwise become ischemic.
anterior cerebral circulation • The anterior cerebral circulation is the blood supply to the anterior portion of the brain. It is supplied by the following arteries: • Internal carotid arteries: These large arteries are the left and right branches of the common carotid arteries in the neck which enter the skull, as opposed to the external carotid branches which supply the facial tissues. The internal carotid artery branches into the anterior cerebral artery and continues to form the middle cerebral artery • Anterior cerebral artery (ACA) • Anterior communicating artery: Connects both anterior cerebral arteries, within and along the floor of the cerebral vault. • Middle cerebral artery (MCA)
posterior cerebral circulation • The posterior cerebral circulation is the blood supply to the posterior portion of the brain, including the occipital lobes, cerebellum and brainstem. It is supplied by the following arteries: • Vertebral arteries: These smaller arteries branch from the subclavian arteries. Within the cranium the two vertebral arteries fuse into the basilar artery. • Posterior inferior cerebellar artery (PICA) is a branch of vertebral artery • Basilar artery: Supplies the midbrain, cerebellum, and usually branches into the posterior cerebral artery • BRANCHES OF BASILAR ARTERY • Anterior inferior cerebellar artery (AICA) • Pontine branches • Superior cerebellar artery (SCA) • Posterior cerebral artery (PCA) • Posterior communicating artery
venous drainage The venous drainage of the cerebrum can be separated into two subdivisions: superficial and deep. The superficial system is composed of dural venous sinuses, which have wall composed of dura mater as opposed to a traditional vein. The dural sinuses are, therefore located on the surface of the cerebrum. The most prominent of these sinuses is the superior sagittal sinus which flows in the sagittal plane under the midline of the cerebral vault, forming the confluence of sinuses, where the superficial drainage joins with the sinus the primarily drains the deep venous system. From here, two transverse sinuses bifurcate and travel laterally and inferiorly in an S-shaped curve that form the sigmoid sinuses which go on to form the two jugular veins. In the neck, the jugular veins parallel the upward course of the carotid arteries and drain blood into the superior vena cava.
The deep venous drainage is primarily composed of traditional veins inside the deep structures of the brain, which join behind the midbrain to form the vein of Galen. This vein merges with the inferior sagittal sinus to form the straight sinus which then joins the superficial venous system mentioned above at the confluence of sinuses.
blood–brain barrier (BBB The blood–brain barrier (BBB) is a separation of circulating blood from the brain extracellular fluid in the central nervous system (CNS). It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion of microscopic objects (e.g., bacteria) and large or hydrophilic molecules into the cerebrospinal fluid (CSF), while allowing the diffusion of small hydrophobic molecules (O2, CO2, hormones). Cells of the barrier actively transport metabolic products such as glucose across the barrier with specific proteins. This barrier also includes a thick basement membrane and astrocytic endfeet
Cerebrovascular Accident • Results from ischemia to a part of the brain or hemorrhage into the brain that results in death of brain cells. • Physical, cognitive, emotional, & financial impact
Cerebrovascular AccidentRisk Factors • Nonmodifiable: • Age – Occurrence doubles each decade >55 years • Gender – Equal for men & women; women die more frequently than men • Race – African Americans, Hispanics, Native Americans, Asian Americans -- higher incidence • Heredity – family history, prior transient ischemic attack, or prior stroke increases risk
Cerebrovascular AccidentRisk Factors Controllable Risks with Medical Treatment & Lifestyle Changes: High blood pressure DiabetesCigarette smoking TIA (Aspirin)High blood cholesterol ObesityHeart Disease Atrial fibrillation Oral contraceptive use Physical inactivity Sickle cell disease Asymptomatic carotid stenosisHypercoagulability
Cerebrovascular AccidentAnatomy of Cerebral Circulation • Blood Supply • Anterior: Carotid Arteries – middle & anterior cerebral arteries • frontal, parietal, temporal lobes; basal ganglion; part of the diencephalon (thalamus & hypothalamus) • Posterior: Vertebral Arteries – basilar artery • Mid and lower temporary & occipital lobes, cerebellum, brainstem, & part of the diencephalon • Circle of Willis – connects the anterior & posterior cerebral circulation
Cerebrovascular AccidentAnatomy of Cerebral Circulation • Blood Supply • 20% of cardiac output—750-1000ml/min • >30 second interruption– neurologic metabolism is altered; metabolism stops in 2 minutes; brain cell death < 5 mins.
Cerebrovascular AccidentPathophysiology • Atherosclerosis: major cause of CVA • Thrombus formation & emboli development • Abnormal filtration of lipids in the intimal layer of the arterial wall • Plaque develops & locations of increased turbulence of blood - bifurcations • Increased turbulence of blood or a tortuous area • Calcified plaques rupture or fissure • Platelets & fibrin adhere to the plaque • Narrowing or blockage of an artery by thrombus or emboli • Cerebral Infarction: blocked artery with blood supply cut off beyond the blockage
Cerebrovascular AccidentPathophysiology • Ischemic Cascade • Series of metabolic events • Inadequate ATP adenosine triphosphate production • Loss of ion homeostasis • Release of excitatory amino acids – glutamate • Free radical formation • Cell death
CVA? - Alarming signs • Sudden numbness or weakness of face, arm, or leg, especially on one side of the body. • Sudden confusion or trouble speaking or understanding speech. • Sudden trouble seeing in one or both eyes. • Sudden trouble walking, dizziness, or loss of balance or coordination • Sudden severe headache with no known cause.
Cerebrovascular AccidentTransient Ischemic Attack • Temporary focal loss of neurologic function • Caused by ischemia of one of the vascular territories of the brain • Microemboli with temporary blockage of blood flow • Lasts less than 24 hrs – often less than 15 mins • Most resolve within 3 hours • Warning sign of progressive cerebrovascular disease
Cerebrovascular AccidentClassifications Based on underlying pathophysiologic findings
Cerebrovascular AccidentClassifications • Ischemic Stroke • Thrombotic • Embolic • Hemorrhagic Stroke • Intracerebral Hemorrhage • Subarachnoid Hemorrhage • Aneurysm
Cerebrovascular AccidentClassifications • Ischemic Stroke—inadequate blood flow to the brain from partial or complete occlusions of an artery--85% of all strokes • Extent of a stroke depends on: • Rapidity of onset • Size of the lesion • Presence of collateral circulation • Symptoms may progress in the first 72 hours as infarction & cerebral edema increase • Types of Ischemic Stroke: Thrombotic StrokeEmbolic Stroke
Cerebrovascular AccidentIschemic – Thrombotic Stroke • Lumen of the blood vessels narrow – then becomes occluded – infarction • Associated with HTN and Diabetes Mellitus • >60% of strokes • 50% are preceded by TIA • – results in considerable deficits – motor hemiplegia, contralateral loss of sensation or motor ability
Cerebrovascular AccidentIschemic – Embolic Stroke • Embolus lodges in and occludes a cerebral artery • Results in infarction & cerebral edema of the area supplied by the vessel • Second most common cause of stroke – 24% • Emboli originate in endocardial layer of the heart – atrial fibrillation, MI, infective endocarditis, rheumatic heart disease, valvular prostheses • Rapid occurrence with severe symptoms – body does not have time to develop collateral circulation • Any age group • Recurrence common if underlying cause not treated
Cerebrovascular AccidentHemorrhagic Stroke • Hemorrhagic Stroke • 15% of all strokes • Result from bleeding into the brain tissue itself • Intracerebral • Subarachnoid
Cerebrovascular AccidentHemorrhage Stroke Intracerebral Hemorrhage • Rupture of a vessel • Hypertension – most important cause • Others: vascular malformations, coagulation disorders, anticoagulation, trauma, brain tumor, ruptured aneurysms • Sudden onset of symptoms with progression • Neurological deficits, headache, nausea, vomiting, and hypertension • Prognosis: poor
Cerebrovascular AccidentHemorrhagic-Subarachnoid • Hemorrhagic Stroke–Subarachnoid Hemorrhage • Intracranial bleeding into the cerebrospinal fluid-filled space between the arachnoid and pia mater membranes on the surface of the brain
Cerebrovascular AccidentHemorrhagic-Subarachnoid • Commonly caused by rupture of cerebral aneurysm (congenital or acquired) • Saccular or berry – few to 20-30 mm in size • Majority occur in the Circle of Willis • Other causes: Arteriovenous malformation (AVM), trauma, illicit drug abuse
Cerebrovascular AccidentClinical Manifestations • Motor Function Impairment • Caused by destruction of motor neurons in the pyramidal pathway (brain to spinal cord) • Mobility • Respiratory function • Swallowing and speech • Gag reflex • Self-care activities • Sensory loss of contralateral side
Cerebrovascular AccidentClinical Manifestations • Psycosocial issues • Difficulty controlling emotions • Exaggerated or unpredictable emotional response • Depression / feelings regarding changed body image and loss of function
Cerebrovascular AccidentClinical Manifestations • Communication • Left hemisphere dominant for language skills in the right-handed person & most left-handed persons -- Aphasia/Dysphasia • Involvement Expression & Comprehension • Receptive Aphasia (Wernicke’s area): sounds of speech nor its meaning can be understood – spoken & written • Expressive Aphasia (Broca’s area): difficulty in speaking and writing • Dysarthria: Affects the mechanics of speech due to muscle control disturbances – pronunciation, articulation, and phonation
Cerebrovascular AccidentTreatment Goals • Prevention • Drug Therapy • Surgical Therapy • Rehabilitation
Cerebrovascular AccidentTreatment Goals • Prevention – Health Maintenance Focus: • Healthy diet • Weight control • Regular exercise • No smoking • Limit alcohol consumption • Route health assessment • Control of risk factors
Cerebrovascular AccidentDiagnostic Studies • Done to confirm CVA and identify cause • Carotid doppler studies (ultrasound study) • CT – primary – identifies size, location, differentiates between ischemic and hemorrhagic • CTA – CT Angiography – visualizes vasculature • MRI – greater specificity than CT • May not be able to be used on all patients (metal, claustrophobia) • Angiography: gold standard for imaging carotid arteries
Cerebrovascular AccidentTreatment Goals • Drug Therapy – Thrombotic CVA – to reestablish blood flow through a blocked artery • Thrombolytic Drugs: tPA (tissue plasminogen activator) • Administered within 3 hours of symptoms of ischemic CVA • Confirmed DX with CT • Patient anticoagulated
CVA - Treatment Goals • Surgical Treatment • Carotid endarterectomy – preventive – > 100,000/year • removal of atheromatous lesions • Clipping, wrapping, coiling Aneurysm . • Treatment of AV Malformations
Cerebrovascular AccidentNursing Diagnoses • Ineffective tissue perfusion r/t decreased cerebrovascular blood flow • Ineffective airway clearance • Impaired physical mobility • Impaired verbal communication • Impaired swallowing • Unilateral neglect r/t visual field cut & sensory loss • Impaired urinary elimination • Situational low self-esteem r/t actual or perceived loss of function
Cerebrovascular AccidentNursing Goals • Maintain stable or improved LOC • Attain maximum physical functioning • Attain maximum self-care activities & skills • Maintain stable body functions • Maximize communication abilities • Maintain adequate nutrition • Avoid complications of stroke • Maintain effective personal & family coping
Cerebrovascular AccidentRehabilitation • Assess: Swallowing; Communication; Complications; motor and sensory function • Speech Therapy—assess swallowing • Physical Therapy—ambulation/strengthening • Bowel/Bladder • Appropriate self-help resources
CNS INFECTIONS • 5 basic TYPES • Acute meningitis: acute bacterial or viral infection of meninges and csf • Encephalitis: acute, subacute or chronic viral infection of brain • Meningoencephalitis: chronic bacterial infection of brain and meningitis • Brain abscess: acute infection of cns parenchyma and subdural spaces (subdural empyema) • Fungal and parasitic infection:
Routes of infection • Hematogenous spread most common usually arterial • Direct implantation usually traumatic • Local extension from sinus infection etc • Axonal transport along peripheral nerves e.g. in rabies
ACUTE BACTERIAL(PYOGENIC) MENINGITIS • S/S FEVER, HEADACHE, NECK STIFFNESS Peak incidence in children PATHOLOGY CSF is cloudy and purulent with neutrophils and organisms Meningeal vessels engorged, may become inflammed and occluded leading to infarction of brain tissue
