REPONSE OF BRAIN TISSUE TO TRAUMA

1. REPONSE OF BRAIN TISSUE TO TRAUMA INTRACRANIAL PRESSURE

2. 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

3. 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

4. Components of the Brain Fig. 55-1

5. Intracranial Pressure • Normal ICP = 4 -15 mmHg • Factors that influence ICP • Arterial pressure • Venous pressure • Intraabdominal and intrathoracic pressure • Posture • Temperature • Blood gases (CO2 levels)

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

7. Intracranial PressureRegulation 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

8. Intracranial Volume-Pressure Curve Fig. 55-2

9. Intracranial PressureRegulation and Maintenance • Normal compensatory adaptations • Alteration of CSF absorption or production • Displacement of CSF into spinal subarachnoid space • Dispensability of the dura

10. Intracranial PressureCerebral 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

11. Intracranial PressureImportance of ICP to BP and CPP • Brain needs constant supply O2 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 O2 & nutrients

12. Intracranial PressureImportance of ICP to BP and CPP • MAP is the DRIVING FORCE • ICP is the RESISTENCE • CPP = MAP – ICP = 100 mmHg – 15 mmHg = 85 mmHg (Normal) CPP < 50 mmHg→ cerebral ischemia CPP < 30 mmHg → brain death

13. Intracranial Pressure:Regulatory Mechanisms ofCerebral Blood Flow • Autoregulation of cerebral blood flow • Metabolic Regulation of cerebral blood flow

14. Intracranial Pressure:Regulatory Mechanisms ofCerebral 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

15. Intracranial Pressure:Regulatory Mechanisms ofCerebral 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

16. Intracranial Pressure: Regulatory Mechanismsof Cerebral Blood Flow • Metabolic Regulation of cerebral blood flow Factors affecting cerebral blood flow • PCO2 • PO2 • Acidosis

17. Increased Intracranial PressureMechanisms of Increased ICP • Causes • Mass lesion • Cerebral edema • Head injury • Brain inflammation • Metabolic insult

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

19. Increased Intracranial Pressure Fig. 55-3

20. Herniation Fig. 55-4

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

22. Increased Intracranial PressureNursing 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)

23. Decorticate and Decerebrate Posturing Fig. 55-6

24. Increased Intracranial PressureNursing Care: Assessment • Headache • Often continuous and worse in the morning • Vomiting • Not preceded by nausea • Projectile

25. Increased Intracranial PressureCollaborative Care • Hyperventilation therapy: suctioning → hyperventilate with 100% oxygen • Adequate oxygenation • PaO2 maintenance at 100 mm Hg or greater • ABG analysis guides the oxygen therapy • May require mechanical ventilator

26. Increased Intracranial PressureCollaborative Care • Drug therapy • Mannitol • Loop diuretics • Corticosteroids • Barbiturates • Antiseizure drugs

27. Increased Intracranial PressureCollaborative Care • Nutritional therapy • Patient is in hypermetabolic and hypercatabolic state •  Need for glucose • Keep patient normovolemic • IV 0.45% or 0.9% sodium chloride

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

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