Pathophysiology Module 9

It is important for the nurse to understand that as intracranial pressure rises above normal limits and compensatory mechanisms fail

neurons can be injured and a change in level of consciousness occurs.

Brain herniation is the movement of the brain from a compartment of high pressure to a compartment of lower pressure. The movement of the brain

increases hypoxia and ischemic injury to brain tissue, reducing the level of consciousness.

Which parts of the brain and its structures contribute to the formation cranial pressure?

Blood, brain tissue, and cerebral spinal fluid

What does the Monro- Kellie hypothesis state?

Small increase in volume can be compensated for by one or both of the other components.

Trama in the Head

Trama in the head can cause head injury. When it happens, it is important to monitor intracranial pressure for disruption. Which can lead to additional brain injury.

What are the three components of intracranial pressure (ICP)?

Brain tissue, Cranial spinal fluid, cranial blood flow

Cerebral blood flow (3-10%)

The brain is able to utilize autoregulation to maintain cerebral perfusion despite changes in systemic blood pressure.

How does cerebral perfusion change in systemic blood pressure?

It does this by dilating or constricting the cerebral arteries depending on arterial pressure.

What is the normal range for ICP

0-15 mm Hg

Brain Tissue (80%)

The brain tissue is the last component to adjust to changes in ICP. The brain can compensate for small changes in ICP by partial collapse of the cisterns, ventricles, and vascular systems. When compensation is not sufficient, brain herniation occurs.

Cerebral Spinal Fluid (8-12%)

Cerebral spinal fluid (CSF) circulates in a closed system of the ventricles, subarachnoid space, and down and around the spinal column. The arachnoid villi absorb the cerebral spinal fluid. Any changes in the cycle of CSF production, circulation, and absorption can affect ICP.

Primary Brain Injuries

Caused by initial trauma

What are the results in immediate disruption for a primary brain injuries

• Skull

• Brain structures (meninges, blood vessels, brain tissue, neurons)

• Brain functions (blood flow, oxygenation, cellular metabolism)

Secondary Brain Injuries Result in

• Cerebral infarction

• Coma

• Increased cerebral edema

Secondary Brain Injuries that are caused by effects of primary injury

• Uncontrolled ICP

• Cerebral ischemia

• Hypotension

• Hypoxemia

• Local or systemic infection

Intracerebral Pressure

Cerebral spinal fluid and cranial blood flow may be able to adjust to relieve ICP.

Signs of increased Intracerebral Pressure

Increased intracerebral pressure can progress quickly

Some signs of increased Intracerebral Pressure

• Level of consciousness

• Pupi size and reaction to light

• Motor function

• Vital signs

• other signs

Early signs of increased Intracerebral Pressure

• Consciousness: Decreased alertness to drowsiness

• Pupil size and reaction to light: Small and sluggish reaction

• Motor Function: Hemiparesis

• Vital signs: No change

• other signs: Hache, slurred speech

Late signs of increased Intracerebral Pressure

• Consciousness: Stupor or coma

• Pupil size and reaction to light: Large and nonreactive

• Motor Function: Hemiplegia

• Vital signs: Hypertension, widened pulse pressure, bradycardia, abnormal respiratory patterns

• other signs: Vomiting

Cerebral edema

It is a secondary brain injury that occurs as a result of a primary brain injury.

Cerebral edema (swelling of brain tissue) results from abnormal water accumulation from intracellular fluid.

Cerebral edema Disorders

These disorders cause an expansion of brain tissue, and this expansion within the solid cranial vault causes decreased cerebral fluid circulation leading to hypoxia.

The first type of Cerebral edema

• Cytotoxic - Results from intracellular sodium potassium pump failure

The second type of Cerebral edema

Vasogenic - Results from disruption to blood- brain barrier

Brain herniation

Occurs when pressure within the cranium is greater than what the brain can compensate for. When pressure increase to this high of a level, it causes brain tissue to be displaced.

Normal Brain

Herniated Brain

Herniation associated with brainstem compression is called central herniation, whereas herniation associated with the supratentorial structures is called uncal (transtentorial) herniation.

Which key points would you include when helping a new nurse understand increased ICP?

• ICP above 15 mm Hg is considered cerebral hypertension.

• Nurses must carefully monitor signs and symptoms of increased ICP to prevent secondary brain injury.

• Decreasing compliance of cranial components to maintain equilibrium results in increased ICP.