REPONSE OF BRAIN TISSUE TO TRAUMA INTRACRANIAL PRESSURE

Intracranial Pressure • Response of brain tissue to trauma occurs at the cellular level: – Injury: massive vasodilation – Cerebral edema: increase in size and volume of brain • Increased ICP: – Increase in pressure exerted within the cranial cavity

Intracranial Pressure • Skull has three essential components: - Brain tissue = 78% - Blood = 12% - Cerebrospinal fluid (CSF) = 10% • Any increase in any of these tissues causes increased ICP

Components of the Brain Fig. 55 -1

Intracranial Pressure • Normal ICP = 4 -15 mm. Hg • Factors that influence ICP – Arterial pressure – Venous pressure – Intraabdominal and intrathoracic pressure – Posture – Temperature – Blood gases (CO 2 levels)

Intracranial Pressure • The degree to which these factors ICP depends on the ability of the brain to accommodate to the changes

Intracranial Pressure Regulation and Maintenance • Normal intracranial pressure – The pressure exerted by the total volume from the brain tissue, blood, and CSF – If the volume in any one of the components increases within the cranial vault and the volume from another component is displaced, the total intracranial volume will not change

Intracranial Volume-Pressure Curve Fig. 55 -2

Intracranial Pressure Regulation and Maintenance • Normal compensatory adaptations – Alteration of CSF absorption or production – Displacement of CSF into spinal subarachnoid space – Dispensability of the dura

Intracranial Pressure Cerebral Blood Flow • Definition – The amount of blood in milliliters passing through 100 g of brain tissue in 1 minute – About 50 ml/min per 100 g of brain tissue

Intracranial Pressure Importance of ICP to BP and CPP – Brain needs constant supply O 2 and Glucose – BP: heart delivers blood to brain at an average BP of 120/80 (Mean BP = 100); this mean arterial pressure (MAP) must be higher than ICP – CPP (Cerebral Perfusion Pressure): is the pressure needed to overcome ICP in order to deliver O 2 & nutrients

Intracranial Pressure Importance of ICP to BP and CPP – MAP is the DRIVING FORCE – ICP is the RESISTENCE – CPP = MAP – ICP = 100 mm. Hg – 15 mm. Hg = 85 mm. Hg (Normal) CPP < 50 mm. Hg→ cerebral ischemia CPP < 30 mm. Hg → brain death

Intracranial Pressure: Regulatory Mechanisms of Cerebral Blood Flow • Autoregulation of cerebral blood flow • Metabolic Regulation of cerebral blood flow

Intracranial Pressure: Regulatory Mechanisms of Cerebral Blood Flow • Autoregulation – The automatic alteration in the diameter of the cerebral blood vessels to maintain a constant blood flow to the brain – Maintains CPP regardless of changes in BP

Intracranial Pressure: Regulatory Mechanisms of Cerebral Blood Flow • Problem: Autoregulation is limited • If BP and/or ICP rises: Autoregulation fails • When autoregulation fails, blood flow to brain increases or deceases → poor perfusion and cellular ischemia or death

Intracranial Pressure: Regulatory Mechanisms of Cerebral Blood Flow • Metabolic Regulation of cerebral blood flow Factors affecting cerebral blood flow – PCO 2 – PO 2 – Acidosis

Increased Intracranial Pressure Mechanisms of Increased ICP • Causes – Mass lesion – Cerebral edema – Head injury – Brain inflammation – Metabolic insult

Increased Intracranial Pressure Mechanisms of Increased ICP • Sustained increases in ICP result in brainstem compression and herniation of the brain from one compartment to another

Increased Intracranial Pressure Fig. 55 -3

Herniation Fig. 55 -4

Increased Intracranial Pressure Nursing Care: Assessment • Change in level of consciousness • Changes in vital signs (Cushing triad) – Widening pulse pressure – Tachy/Bradycardia – Increased systolic BP – Irregular respirations

Increased Intracranial Pressure Nursing Care: Assessment • Ocular signs • Decrease in motor strength and function – Assess movement – Assess response to stimuli – Assess: • Decerebrate posturing (extensor) – Indicates more serious damage • Decorticate posturing (flexor)

Decorticate and Decerebrate Posturing Fig. 55 -6

Increased Intracranial Pressure Nursing Care: Assessment • Headache – Often continuous and worse in the morning • Vomiting – Not preceded by nausea – Projectile

Increased Intracranial Pressure Collaborative Care • Hyperventilation therapy: suctioning → hyperventilate with 100% oxygen • Adequate oxygenation – Pa. O 2 maintenance at 100 mm Hg or greater – ABG analysis guides the oxygen therapy – May require mechanical ventilator

Increased Intracranial Pressure Collaborative Care • Drug therapy – Mannitol – Loop diuretics – Corticosteroids – Barbiturates – Antiseizure drugs

Increased Intracranial Pressure Collaborative Care • Nutritional therapy – Patient is in hypermetabolic and hypercatabolic state – Need for glucose – Keep patient normovolemic • IV 0. 45% or 0. 9% sodium chloride

Increased Intracranial Pressure Nursing Management Overall goals: • ICP WNL • Maintain patent airway • Normal fluid and electrolyte balance • No complications secondary to immobility • Respiratory function • Fluid and electrolyte balance

Increased Intracranial Pressure Nursing Management Overall goals (cont’d) • Body position maintained in head-up position: elevate HOB 30° • Protection from injury: positioning/turning • Pain control • Psychologic considerations