Intracranial Pressure

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

Fig. 55-1

Components of the Brain

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)

Intracranial Pressure

The degree to which these factors  ICPdepends on the ability of the brain to accommodate to the changes

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



Fig. 55-2

Intracranial Volume-Pressure Curve

Intracranial PressureRegulation and Maintenance


Normal compensatory adaptations Alteration of CSF absorption or production Displacement of CSF into spinal subarachnoid space Dispensability of the dura

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

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

Intracranial PressureImportance of ICP to BP and CPP

MAP is the DRIVING FORCEICP is the RESISTENCECPP = MAP – ICP = 100 mmHg – 15 mmHg = 85 mmHg (Normal)CPP < 50 mmHg→ cerebral ischemiaCPP < 30 mmHg → 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 limitedIf BP and/or ICP rises: Autoregulation failsWhen 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 PCO2 PO2 Acidosis

Increased Intracranial PressureMechanisms of Increased ICP

Causes Mass lesion Cerebral edema Head injury Brain inflammation Metabolic insult

Increased Intracranial PressureMechanisms of Increased ICP

Sustained increases in ICP result in brainstem compression and herniation of the brain from one compartment to another

Fig. 55-3

Increased Intracranial Pressure

Fig. 55-4

Herniation

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

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)

Fig. 55-6

Decorticate and Decerebrate Posturing

Increased Intracranial PressureNursing Care: Assessment

Headache Often continuous and worse in the morning Vomiting Not preceded by nausea Projectile

Increased Intracranial PressureCollaborative Care

Hyperventilation therapy: suctioning →hyperventilate with 100% oxygenAdequate oxygenationPaO2 maintenance at 100 mm Hg or greaterABG analysis guides the oxygen therapyMay require mechanical ventilator

Increased Intracranial PressureCollaborative Care

Drug therapy Mannitol Loop diuretics Corticosteroids Barbiturates Antiseizure drugs

Increased Intracranial PressureCollaborative Care

Nutritional therapyPatient is in hypermetabolic and hypercatabolic state Need for glucoseKeep patient normovolemicIV 0.45% or 0.9% sodium chloride

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

Increased Intracranial PressureNursing Management

Overall goals (cont’d) Body position maintained in head-up position: elevate HOB 30°Protection from injury: positioning/turningPain controlPsychologic considerations