BIOC33H3 Lecture Notes - Aphasia, Drug Resistance, Sinusitis

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25 Mar 2013
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Chapter 57: Acute Intracranial Problems
NORMAL INTRACRANIAL PRESSURE
Intracranial pressure (ICP) is the hydrostatic force measured in the brain CSF compartment.
Normal ICP is the total pressure exerted by the three components within the skull: brain tissue,
blood, and CSF.
If the volume of any one of the three components increases within the cranial vault and the
volume from another component is displaced, the total intracranial volume will not change.
ICP can be measured in the ventricles, subarachnoid space, subdural space, epidural space, or
brain parenchymal tissue using a pressure transducer. Normal intracranial ICP ranges from 0 to
15 mm Hg.
A sustained pressure above the upper limit is considered abnormal. ICP may rise due to head
trauma, stroke, subarachnoid hemorrhage, brain tumor, inflammation, hydrocephalus, or brain
tissue damage from other causes.
CRANIAL BLOOD FLOW
Cerebral blood flow (CBF) is the amount of blood in milliliters passing through 100 g of brain
tissue in 1 minute.
Through a process known as autoregulation, the brain has the ability to regulate its own blood
flow in response to its metabolic needs despite wide fluctuations in systemic arterial pressure.
The cerebral perfusion pressure (CPP) is the pressure needed to ensure blood flow to the brain.
As the CPP decreases, autoregulation fails and CBF decreases, which can lead to ischemia and
neuronal death.
Compliance is the expandability of the brain. With low compliance, small changes in volume
result in greater increases in pressure.
INCREASED INTRACRANIAL PRESSURE
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Increased ICP is a life-threatening situation that results from an increase in any or all of the
three components (brain tissue, blood, CSF) within the skull. Cerebral edema is an important
factor contributing to increased ICP.
Elevated ICP is clinically significant because it diminishes CPP, increases risks of brain ischemia
and infarction, and is associated with a poor prognosis.
The clinical manifestations of increased ICP can take many forms, depending on the cause,
location, and rate at which the pressure increase occurs. Complications of ICP include changes in
the level of consciousness, changes in vital signs, dilation of pupils, decrease in motor function,
headache, and vomiting.
The earlier the condition is recognized and treated, the better the patient outcome.
The major complications of uncontrolled increased ICP are inadequate cerebral perfusion and
cerebral herniation.
ICP monitoring is used to guide clinical care when the patient is at risk for or has elevations in
ICP. It may be used in patients with a variety of neurologic insults, including hemorrhage, stroke,
tumor, infection, or traumatic brain injury.
The “gold standard” for monitoring ICP is the ventriculostomy, in which a specialized catheter is
inserted into the right lateral ventricle and coupled to an external transducer. Other devices
now allow for an indirect assessment of cerebral oxygenation and perfusion.
With the ventricular catheter and certain fiberoptic systems, it is possible to control ICP by
removing CSF. The level of the ICP at which to initiate drainage, amount of fluid to be drained,
height of the system, and frequency of drainage are ordered by the physician.
The goals of collaborative care are to identify and treat the underlying cause of increased ICP
and to support brain function.
Drug therapy plays an important part in the management of increased ICP. An osmotic diuretic,
corticosteroids, and barbiturates may be prescribed.
All patients must have their nutritional needs met, regardless of their state of consciousness or
health. Early feeding following brain injury may improve outcomes.
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The Glasgow Coma Scale is a quick, practical, and standardized system for assessing the degree
of impaired consciousness that should be used during nursing assessment. Also during
assessment, the pupils are compared to one another for size, shape, movement, and reactivity.
The overall nursing goals are that the patient with increased ICP will (1) maintain a patent
airway, (2) have ICP within normal limits, (3) demonstrate normal fluid and electrolyte balance,
and (4) have no complications secondary to immobility and decreased level of consciousness.
Maintenance of a patent airway is critical in the patient with increased ICP and is a primary
nursing responsibility. As the level of consciousness decreases, the patient is at increased risk of
airway obstruction from the tongue dropping back and occluding the airway or from
accumulation of secretions.
The patient with increased ICP should be maintained in the head-up position. The nurse must
take care to prevent extreme neck flexion, which can cause venous obstruction and contribute
to elevated ICP.
The patient with increased ICP and a decreased level of consciousness needs protection from
self-injury. Confusion, agitation, and the possibility of seizures increase the risk for injury.
HEAD INJURY
Head injury includes any trauma to the scalp, skull, or brain. The term head trauma is used
primarily to signify craniocerebral trauma, which includes an alteration in consciousness, no
matter how brief.
Scalp lacerations are an easily recognized type of external head trauma. Because the scalp
contains many blood vessels with poor constrictive abilities, the major complications associated
with scalp laceration are blood loss and infection.
Skull fractures frequently occur with head trauma. There are several ways to describe skull
fractures: (1) linear or depressed; (2) simple, comminuted, or compound; and (3) closed or
open.
A concussion is a sudden transient mechanical head injury with disruption of neural activity and
a change in the LOC and is considered a minor head injury.
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